Molecular absorption spectrophotometry (Milner et al., 1952), atomic absorption spectrometry (AAS), (Langmyhr and Aadalen,1980), inductively coupled plasma-optical emission spectrometry (ICP-OES) (Fabbe and Ruschak, 1985), inductively coupled plasma mass spectrometry (ICP-MS) (Lord et al., 1991), high performance liquid chromatography (HPLC) (Khuhawar and Lanjwani, 1996), gas chromatography (GC) (Delli and Patsalide, 1981), capillary electrophoreses, (Mirza et al., 2009) and X-ray fluorescence spectroscopy (XFS) (Vilhunen et al., 1997) methods have been reported for the determination of metals in crude oils.

#### **3.1 Sample preparation**

Crude oil is a complex matrix of varying viscosities and mixed phases (organic, water and particulate matter) and therefore not an ideal matrix for analysis. The determination of the metals in crude oil requires pretreatment to the sample before presentation to the instrument. This is the stage where most of the errors occur and is time consuming. The selection of a particular procedure depends upon (1) analytical technique to be employed, (2) nature and the number of the samples to be analyzed, (3) desired degree of precision and

Determination of Metal Ions in Crude Oils 125

efficiency of acid digestion. US-EPA method 3051 (1994) reported microwave assisted acid digestion procedure for 0.5 g of oil and other samples with 10 ml of nitric acid with 10 min. of heating. Alvarado et al (1990) optimized a procedure for the microwave digestion of crude oil samples using different proportions of HNO3 and H2SO4 for the analysis of Cr, Cu, Fe, Mn, Ni, Na and Zn. Bettinelli et al (1995) examined microwave digestion of fuel oils in a high pressure closed vessel and observed a decrease in sample decomposition time due to higher temperature achieved. Using the conditions, difficult samples were also decomposed completely. Munoz et al (2007) evaluated the use of different microwave ovens for the decomposition of crude oils and diesel fuel to determine the contents of Cu, Pb, Hg and Zn in the diagestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2 operated at atmospheric pressure, and a closed vessel microwave (CVM) oven using HNO3/H2O2, operated under pressure in a vessel, were evaluated. Better detection limits were reported for FM digested solutions with 0.8 – 1.0 g of sample, in contrast low quantities (0.10 – 0.28 g) were used when pressurized vessels were used. However the loss of Hg was verified when samples were decomposed in the FM oven. Sant' Ana et al (2007) reported focused microwave assisted procedure for the wet acid dissolution of diesel oil for the determination of metals in samples. The dissolution process was monitored by measuring residual carbon content (RCC) after application of digestion program. The dissolution program comprised three steps: (1) carbonization with H2SO4, (2) oxidation with HNO3 and (3) final oxidation with H2O2. It was reported that the first step was important on the dissolution process. At optimized conditions it was possible to digest 2.5 g diesel oil with a 40 min. heating program. At these conditions, residual carbon content was lower than 5%. Optimized methodology was used in the determination of Al, Cu, Fe, Ni and Zn in three diesel oil samples. Pereira et al (2010) described a method for light and heavy crude oil digestion by microwave induced combustion in the closed vessel for the determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V and Zn. Conventional microwave assisted digestion in pressurized vessels were also used for results comparison. Accuracy of microwave-induced combustion method was evaluated for As, Ba, Ni, Se, V and Zn using certified reference material with similar matrix. Recovery tests were better than 97% using 2 mol/L nitric acid as absorbing solution. Both sample preparation techniques were suitable for crude oil digestion, but microwave induced combustion was preferable in the view of possibility of using diluted nitric acid as absorbing solution. Mello et al (2009) applied microwave induced combustion for the determination of Ni, V, S from crude oil distillation residues. The results obtained agreed with certified values for Ni, V and S within 99 to 101%

The dilution of crude oils and derivatives with organic solvents is an attractive sample preparation method, because it is simple and rapid and could be used for the determination of the metals by spectro-analytical techniques. The solvents commonly used are xylene, kerosene, methyl isobutyl ketone (MIBK), n-hexane, dimethylbenzene, 1-propanol and mixture of these solvents. The procedure is widely used in industry (Batho et al., 1993), (Botto and Zhu, 1996). Direct dilution of crude oils and residual fuels with an organic solvent for the determination of Ni, V, Fe and Na is proposed in ASTM standard test method (Standard test methods ASTM D 5863-00 a (2005). Ni and V in crudes and heavy crude fractions were determined after dilution in xylene (Fabec and Ruschak, 1985). The

using 2 mol/L HNO3 as absorbing solution.

**3.1.4 Dilution with organic solvents**

accuracy required, (4) availability of the equipment, materials and reagents and (5) the cost of analysis (Oliveira et al., 2003). It is generally desired that analysis is completed within shortest time with minimum contamination, using smallest quantities of the reagents and the samples and little residues and waste generation (Amorin et al., 2007).

Metal determination in crude oil is carried out by using dry ashing, dilution in organic solvents (Annual Book of ASTM, 2000, 2002) or using micro-emulsions (Souza et al., 2006), (Santella et al., 2008). The use of micro-wave radiation as a potential sample preparation technique has been applied due to high efficiency of heat transfer and sample digestion efficiency (Mello et al., 2009), (Perira et al., 2010). Literature data concerning metal and metalloid determinations in the crude oil by direct sample introduction is also available (Anselmi et al., 2002), (de Oliveira et al., 2006).

#### **3.1.1 Sample decomposition by ashing**

Drug ashing is used for complete elimination of organic matter, before analytical determination and is based on the ignition of the organic matrix in air or in the stream of oxygen, followed by the dissolution of the residue in an acid medium. This is one of the cheapest sample preparation procedure. Larger quantities of the sample could be used and the analyte could be concentrated into small volume of dilute mineral acid (HCl or HNO3). This also make possible the use of aqueous standards for the calibration of equipment. The main disadvantages of the dry ashing procedure for crude oils are the risks of contamination or loss of the analyte due to the formation of volatile compounds. (Ekanem et al., 1998). The addition of sulphur containing compounds has long been used for avoiding losses of Ni and V by volatization during ashing (Udoh et al., 1992). The dry ashing takes longer time for sample preparation with low sample preparation frequency.

#### **3.1.2 Sample decomposition by wet digestion**

The sample decomposition of organic constituents by wet digestion is achieved by the use of oxidizing agents prior to analyte determination. Normally concentrated acids are applied under heating, and the important aspects for consideration are the strength of the acids, their oxidizing and complexing power, their boiling points, the solubility of the resulting salts, safely in manipulation and purity (Amorim et al., 2007). The acids and oxidizing agents used for oil samples include mixtures of nitric, hydrochloric and sulphuric acids and hydrogen peroxide. This is also one way to overcome the difference in response caused by the presence of different analyte compounds in the fuel by their conversion in water soluble salts. The procedure is generally performed with larger volume of oxidizing acids (e.g. 10 ml of acid per 0.5 g of sample) and time for complete decomposition is long (up to several days). The use of sulphuric acid in wet digestion procedure for trace metal determination in oils, suggested in literature has been reapproved as standard methods for the determination of Ni, V and Fe in crude oils and residual fuels (Standard test methods, 2005).

#### **3.1.3 Wet digestion assisted by microwave radiation**

Wet digestions assisted by microwave radiation have been observed as safer and efficient. The procedures minimize contamination and amount of reagents for sample preparations (Ozcan and Akman, 2005), (Trindade et al., 2006). Microwave heating enhances the

accuracy required, (4) availability of the equipment, materials and reagents and (5) the cost of analysis (Oliveira et al., 2003). It is generally desired that analysis is completed within shortest time with minimum contamination, using smallest quantities of the reagents and

Metal determination in crude oil is carried out by using dry ashing, dilution in organic solvents (Annual Book of ASTM, 2000, 2002) or using micro-emulsions (Souza et al., 2006), (Santella et al., 2008). The use of micro-wave radiation as a potential sample preparation technique has been applied due to high efficiency of heat transfer and sample digestion efficiency (Mello et al., 2009), (Perira et al., 2010). Literature data concerning metal and metalloid determinations in the crude oil by direct sample introduction is also available

Drug ashing is used for complete elimination of organic matter, before analytical determination and is based on the ignition of the organic matrix in air or in the stream of oxygen, followed by the dissolution of the residue in an acid medium. This is one of the cheapest sample preparation procedure. Larger quantities of the sample could be used and the analyte could be concentrated into small volume of dilute mineral acid (HCl or HNO3). This also make possible the use of aqueous standards for the calibration of equipment. The main disadvantages of the dry ashing procedure for crude oils are the risks of contamination or loss of the analyte due to the formation of volatile compounds. (Ekanem et al., 1998). The addition of sulphur containing compounds has long been used for avoiding losses of Ni and V by volatization during ashing (Udoh et al., 1992). The dry ashing takes longer time for

The sample decomposition of organic constituents by wet digestion is achieved by the use of oxidizing agents prior to analyte determination. Normally concentrated acids are applied under heating, and the important aspects for consideration are the strength of the acids, their oxidizing and complexing power, their boiling points, the solubility of the resulting salts, safely in manipulation and purity (Amorim et al., 2007). The acids and oxidizing agents used for oil samples include mixtures of nitric, hydrochloric and sulphuric acids and hydrogen peroxide. This is also one way to overcome the difference in response caused by the presence of different analyte compounds in the fuel by their conversion in water soluble salts. The procedure is generally performed with larger volume of oxidizing acids (e.g. 10 ml of acid per 0.5 g of sample) and time for complete decomposition is long (up to several days). The use of sulphuric acid in wet digestion procedure for trace metal determination in oils, suggested in literature has been reapproved as standard methods for the determination

Wet digestions assisted by microwave radiation have been observed as safer and efficient. The procedures minimize contamination and amount of reagents for sample preparations (Ozcan and Akman, 2005), (Trindade et al., 2006). Microwave heating enhances the

of Ni, V and Fe in crude oils and residual fuels (Standard test methods, 2005).

**3.1.3 Wet digestion assisted by microwave radiation**

the samples and little residues and waste generation (Amorin et al., 2007).

(Anselmi et al., 2002), (de Oliveira et al., 2006).

sample preparation with low sample preparation frequency.

**3.1.2 Sample decomposition by wet digestion**

**3.1.1 Sample decomposition by ashing**

efficiency of acid digestion. US-EPA method 3051 (1994) reported microwave assisted acid digestion procedure for 0.5 g of oil and other samples with 10 ml of nitric acid with 10 min. of heating. Alvarado et al (1990) optimized a procedure for the microwave digestion of crude oil samples using different proportions of HNO3 and H2SO4 for the analysis of Cr, Cu, Fe, Mn, Ni, Na and Zn. Bettinelli et al (1995) examined microwave digestion of fuel oils in a high pressure closed vessel and observed a decrease in sample decomposition time due to higher temperature achieved. Using the conditions, difficult samples were also decomposed completely. Munoz et al (2007) evaluated the use of different microwave ovens for the decomposition of crude oils and diesel fuel to determine the contents of Cu, Pb, Hg and Zn in the diagestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2 operated at atmospheric pressure, and a closed vessel microwave (CVM) oven using HNO3/H2O2, operated under pressure in a vessel, were evaluated. Better detection limits were reported for FM digested solutions with 0.8 – 1.0 g of sample, in contrast low quantities (0.10 – 0.28 g) were used when pressurized vessels were used. However the loss of Hg was verified when samples were decomposed in the FM oven. Sant' Ana et al (2007) reported focused microwave assisted procedure for the wet acid dissolution of diesel oil for the determination of metals in samples. The dissolution process was monitored by measuring residual carbon content (RCC) after application of digestion program. The dissolution program comprised three steps: (1) carbonization with H2SO4, (2) oxidation with HNO3 and (3) final oxidation with H2O2. It was reported that the first step was important on the dissolution process. At optimized conditions it was possible to digest 2.5 g diesel oil with a 40 min. heating program. At these conditions, residual carbon content was lower than 5%. Optimized methodology was used in the determination of Al, Cu, Fe, Ni and Zn in three diesel oil samples. Pereira et al (2010) described a method for light and heavy crude oil digestion by microwave induced combustion in the closed vessel for the determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V and Zn. Conventional microwave assisted digestion in pressurized vessels were also used for results comparison. Accuracy of microwave-induced combustion method was evaluated for As, Ba, Ni, Se, V and Zn using certified reference material with similar matrix. Recovery tests were better than 97% using 2 mol/L nitric acid as absorbing solution. Both sample preparation techniques were suitable for crude oil digestion, but microwave induced combustion was preferable in the view of possibility of using diluted nitric acid as absorbing solution. Mello et al (2009) applied microwave induced combustion for the determination of Ni, V, S from crude oil distillation residues. The results obtained agreed with certified values for Ni, V and S within 99 to 101% using 2 mol/L HNO3 as absorbing solution.

#### **3.1.4 Dilution with organic solvents**

The dilution of crude oils and derivatives with organic solvents is an attractive sample preparation method, because it is simple and rapid and could be used for the determination of the metals by spectro-analytical techniques. The solvents commonly used are xylene, kerosene, methyl isobutyl ketone (MIBK), n-hexane, dimethylbenzene, 1-propanol and mixture of these solvents. The procedure is widely used in industry (Batho et al., 1993), (Botto and Zhu, 1996). Direct dilution of crude oils and residual fuels with an organic solvent for the determination of Ni, V, Fe and Na is proposed in ASTM standard test method (Standard test methods ASTM D 5863-00 a (2005). Ni and V in crudes and heavy crude fractions were determined after dilution in xylene (Fabec and Ruschak, 1985). The

Determination of Metal Ions in Crude Oils 127

this solution was emulsified by stirring with 3% Triton X-100 in water. Calibrations were prepared with organometallic standards following the same procedure. The emulsions were stable from 20 to 50 min. Good agreement between found and certified results was reported. Vale et al (2004) optimized the emulsification of petroleum for the determination of the nickel. They stabilized samples and analytic solutions as an o/w emulsion consisting of xylene, Triton X-100 and water. Ultrasonic bath was used in the emulsification process and the mixture was further homogenized just before the measurement by manually flushing them with a micropipette. Aucetio et al (2004) determined V in the asphaltene petroleum fraction. The analytic solution was stabilized by mixing with propan-1-ol and 6 mol/L HNO3 forming a detergentless micro-emulsion. The micro-emulsion was immediately formed and was reported to be stable upto 80 h. Calibration was performed by spiking in organic V in the same micro-emulsion medium. A comparison with established methods (acid digestion or dilution in organic solvent) shows that emulsion or micro-emulsion methodology presents advantages in terms of simplicity of sample preparation, total analysis time, long term sample stability and the use of inorganic standards for calibration

Direct analysis using little or no sample preparation has the advantage of time saving and minimum risk of analytic loss. This technique has been applied for highly viscous liquids and has been examined for the determination of Ni (Brandao et al., 2006), Ni and V (Silva et al., 2007) and Cu, Fe and V (Brandao et al., 2007) in oil samples. However there are some general problems such as volatility, flammability and immiscibility with water. In addition to the problems related to the complexity of the matrix, organic standards, which are indispensable in case of direct sample introduction, are unstable and there are no certified reference materials available for these samples. It is therefore necessary to compare the accuracy of the developed method with results obtained with independent technique,

Extraction for the analyte from the fuel can be used for sample preparation, which combines the advantages of separating the analyte from the matrix, transferring it to an aqueous phase and may also result in preconcentration. Liquid-liquid extraction procedures present as main advantage for their simplicity. Akinlua and Smith (2010) reported the extraction of trace metals from petroleum source rock by superheated water and the conditions for maximum yield were determined. The optimum temperature for superheated water extraction of the metals from petroleum source rocks was 250oC. The extraction time was 30 min. The leaching of Cd, Cr, Mn and Ni had better yield with superheated water, while V

Solid phase extraction is a useful separation and preconcentration procedure for the determination of trace metals in fuels. It is based on the partition between a liquid (sample) and a solid phase (sorbent), which can be unloaded, load on chemically modified with organofunctional groups (Koen et al., 2006). After pre-concentration the analyte is recovered

by elution with an appropriate solvent or directly determined in the solid phase.

instead of expensive metal organic standards (Anorim et al., 2007).

**3.1.6 Direct analysis of crude oil**

**3.1.7 Analyte extraction**

had better yield with acid digestion.

particularly with respect to the sample preparation.

solubilisation of crudes and its burning residues was carried out with MIBK for the determination of V as well as Cd and Ni (Guidr and Sneddon, 2002), (Hammond et al., 1998). Bethinelli and Tillarelli (1994) validated a procedure for the determination of Ni and V in fuel oils based on the 1 + 9 dilution with xylene and calibration was with constant organometallic standards, using base oil for matching the viscosity on fuel oil with known metal contents. The procedure was compared with a series of independent methods in the analysis of six samples with different metal contents. The results very close to the consensus values were reported.

Dilution with organic solvents, in spite of simplicity has number of limitations (1) Analyte concentration may change due to the evaporation of the solvent or due to the adsorption on the walls of container (Campos et al., 2002), (2) The problems of plasma destabilization or extinction in case of ICP technique and the contamination of the instrument with carbon residues persist, as the organic load is not reduced with dilution, (3) The toxicity of many organic solvents requires care to avoid and health hazard for laboratory personnel, (4) different metal – organic compounds often exhibit different sensitivity and require use of expensive organic standards for calibration (Vale et al., 2004). The standards may also show a sensitivity difference from that of the metal organic compounds present in the fuel (Teserovsky and Arpadjan, 1991).

#### **3.1.5 Preparation of emulsion**

A fuel sample may be modified by formation of emulsions or micro-emulsion (Three component system). When two immiscible liquids are stirred, a macro emulsion is obtained either oil in water (o/w, droplets of oil in water) or water in oil (w/o, droplets of water in oil), depending on the dispersed phase. In emulsion and micro-emulsion the fuel is dispersed in the aqueous phase as micro drops stabilized by micelles or vesicles generated by the addition of a detergent. The emulsion that is formed is mainly related to the formulation and to the lesser degree to the o/w ratio. In the case of micro-emulsion without detergent a co-solvent allows the formation of a homogenous and long term stable three component solution containing the aqueous and organic phase (das Gracas Andrade Koen et al., 2007), (Pelizzeti and Pramauro, 1985). The procedure enables to use aqueous standards for calibration without the need of sample mineralization. A surfactant with a suitable hydrophilic-lyophilic balance is used in the preparation of emulsion, which permits relatively high solubility between the immiscible phases. In the case of detergentless microemulsions, an alcohol of low molecular weight is added as co-solvent (Cardarelli et al., 1986). Emulsions and micro-emulsions have been successfully applied for the preparation of oil samples, due to homogenous dispersion and stabilization of the oil micro-droplets in aqueous phase, which reduces oil viscosity and the organic load of the system.

Kumat and Gangadharen (1999) applied Triton X-100 emulsions to the determination of V, Co, Ni, As, Hg and Pb in naphtha. Murillo and Chirinos (1994) examined non-ionic emulsifier, polyoxyethylene nonylphenylether for heavy crude oils because of its slightly higher hydrophile-lipophile balance, which enabled higher solubility in water through hydrogen bonding. Souza and da Silveira (2006) reported detergentless emulsions for the determination of elements in crude oils by using acidified water for element stabilization and propan-1-ol as a co-solvent. Meeravali and Kumar (2001) determined Ni and V in naphtha and fuel oils after emulsion formation. The oil samples were diluted in toluene, and

solubilisation of crudes and its burning residues was carried out with MIBK for the determination of V as well as Cd and Ni (Guidr and Sneddon, 2002), (Hammond et al., 1998). Bethinelli and Tillarelli (1994) validated a procedure for the determination of Ni and V in fuel oils based on the 1 + 9 dilution with xylene and calibration was with constant organometallic standards, using base oil for matching the viscosity on fuel oil with known metal contents. The procedure was compared with a series of independent methods in the analysis of six samples with different metal contents. The results very close to the consensus

Dilution with organic solvents, in spite of simplicity has number of limitations (1) Analyte concentration may change due to the evaporation of the solvent or due to the adsorption on the walls of container (Campos et al., 2002), (2) The problems of plasma destabilization or extinction in case of ICP technique and the contamination of the instrument with carbon residues persist, as the organic load is not reduced with dilution, (3) The toxicity of many organic solvents requires care to avoid and health hazard for laboratory personnel, (4) different metal – organic compounds often exhibit different sensitivity and require use of expensive organic standards for calibration (Vale et al., 2004). The standards may also show a sensitivity difference from that of the metal organic compounds present in the fuel

A fuel sample may be modified by formation of emulsions or micro-emulsion (Three component system). When two immiscible liquids are stirred, a macro emulsion is obtained either oil in water (o/w, droplets of oil in water) or water in oil (w/o, droplets of water in oil), depending on the dispersed phase. In emulsion and micro-emulsion the fuel is dispersed in the aqueous phase as micro drops stabilized by micelles or vesicles generated by the addition of a detergent. The emulsion that is formed is mainly related to the formulation and to the lesser degree to the o/w ratio. In the case of micro-emulsion without detergent a co-solvent allows the formation of a homogenous and long term stable three component solution containing the aqueous and organic phase (das Gracas Andrade Koen et al., 2007), (Pelizzeti and Pramauro, 1985). The procedure enables to use aqueous standards for calibration without the need of sample mineralization. A surfactant with a suitable hydrophilic-lyophilic balance is used in the preparation of emulsion, which permits relatively high solubility between the immiscible phases. In the case of detergentless microemulsions, an alcohol of low molecular weight is added as co-solvent (Cardarelli et al., 1986). Emulsions and micro-emulsions have been successfully applied for the preparation of oil samples, due to homogenous dispersion and stabilization of the oil micro-droplets in

aqueous phase, which reduces oil viscosity and the organic load of the system.

Kumat and Gangadharen (1999) applied Triton X-100 emulsions to the determination of V, Co, Ni, As, Hg and Pb in naphtha. Murillo and Chirinos (1994) examined non-ionic emulsifier, polyoxyethylene nonylphenylether for heavy crude oils because of its slightly higher hydrophile-lipophile balance, which enabled higher solubility in water through hydrogen bonding. Souza and da Silveira (2006) reported detergentless emulsions for the determination of elements in crude oils by using acidified water for element stabilization and propan-1-ol as a co-solvent. Meeravali and Kumar (2001) determined Ni and V in naphtha and fuel oils after emulsion formation. The oil samples were diluted in toluene, and

values were reported.

(Teserovsky and Arpadjan, 1991).

**3.1.5 Preparation of emulsion**

this solution was emulsified by stirring with 3% Triton X-100 in water. Calibrations were prepared with organometallic standards following the same procedure. The emulsions were stable from 20 to 50 min. Good agreement between found and certified results was reported. Vale et al (2004) optimized the emulsification of petroleum for the determination of the nickel. They stabilized samples and analytic solutions as an o/w emulsion consisting of xylene, Triton X-100 and water. Ultrasonic bath was used in the emulsification process and the mixture was further homogenized just before the measurement by manually flushing them with a micropipette. Aucetio et al (2004) determined V in the asphaltene petroleum fraction. The analytic solution was stabilized by mixing with propan-1-ol and 6 mol/L HNO3 forming a detergentless micro-emulsion. The micro-emulsion was immediately formed and was reported to be stable upto 80 h. Calibration was performed by spiking in organic V in the same micro-emulsion medium. A comparison with established methods (acid digestion or dilution in organic solvent) shows that emulsion or micro-emulsion methodology presents advantages in terms of simplicity of sample preparation, total analysis time, long term sample stability and the use of inorganic standards for calibration instead of expensive metal organic standards (Anorim et al., 2007).

#### **3.1.6 Direct analysis of crude oil**

Direct analysis using little or no sample preparation has the advantage of time saving and minimum risk of analytic loss. This technique has been applied for highly viscous liquids and has been examined for the determination of Ni (Brandao et al., 2006), Ni and V (Silva et al., 2007) and Cu, Fe and V (Brandao et al., 2007) in oil samples. However there are some general problems such as volatility, flammability and immiscibility with water. In addition to the problems related to the complexity of the matrix, organic standards, which are indispensable in case of direct sample introduction, are unstable and there are no certified reference materials available for these samples. It is therefore necessary to compare the accuracy of the developed method with results obtained with independent technique, particularly with respect to the sample preparation.

#### **3.1.7 Analyte extraction**

Extraction for the analyte from the fuel can be used for sample preparation, which combines the advantages of separating the analyte from the matrix, transferring it to an aqueous phase and may also result in preconcentration. Liquid-liquid extraction procedures present as main advantage for their simplicity. Akinlua and Smith (2010) reported the extraction of trace metals from petroleum source rock by superheated water and the conditions for maximum yield were determined. The optimum temperature for superheated water extraction of the metals from petroleum source rocks was 250oC. The extraction time was 30 min. The leaching of Cd, Cr, Mn and Ni had better yield with superheated water, while V had better yield with acid digestion.

Solid phase extraction is a useful separation and preconcentration procedure for the determination of trace metals in fuels. It is based on the partition between a liquid (sample) and a solid phase (sorbent), which can be unloaded, load on chemically modified with organofunctional groups (Koen et al., 2006). After pre-concentration the analyte is recovered by elution with an appropriate solvent or directly determined in the solid phase.

Determination of Metal Ions in Crude Oils 129

using tungsten coated graphite furnace. The effect of sulphur interference on the determination was examined. The sulphur content less than 1% can be tolerated. An agreement between proposed and comparative procedures was reported. Meeravali and Kumar (2001) analyzed Ni and V in naphtha and fuel oils after emulsion formation by ET-AAS using W-Ir as permanent modifier. The oil samples diluted in toluene was emulsified with 3% Triton X-100 in water. Calibration was performed with organometallic standards prepared in same manner. Burguera et al (2003) analyzed Cr in heavy crude oil and in bitumen in water emulsion by ET-AAS after sample emulsification. Vale et al (2004) optimized the determination of Ni in petroleum using both line source and high resolution continuum source ET-AAS. They stabilized sample and analyte solutions as an emulsion consisting of xylene, Triton X-100 and water. The authors observed a significant Ni loss at pyrolysis temperature of 500 oC, most probably due to the presence of volatile Ni species. However better results were reported at pyrolysis temperature of 400 oC. Aucelio et al (2004) determined V in the asphaltene petroleum fraction by ET-AAS. The solution of the sample was stabilized by mixing with 1-propanol and HNO3, forming detergentless microemulsion. Calibration was performed by spiking inorganic V in the same micro-emulsion medium. Damin et al (2005) determined Ni and V in oil samples by line source ET-AAS, Pd (20 µg) was used as chemical modifier. Good agreement was reported between found and expected values. Quadros et al (2010) determined Ni and V simultaneously as their total and nonvolatile fractions in crude oil samples using high resolution continuum source graphite atomic absorption spectrometry. Determination was carried out at 305.432 nm and 305.633 nm for Ni and V respectively using linear charge – coupled device array detection. Oil-inwater emulsions were used for crude oil sample preparation. Nitric acid was added to emulsion for the determination of total Ni and V concentration. In the absence of acid volatile fraction was lost in the pyrolysis and thermally stable fractions were determined. The concentration of the volatile fraction was obtained by difference. Vale et al (2006) used ET-AAS to differentiate between volatile and nonvolatile Ni and V compounds in crude oil. Two crude oil samples were separated in two steps: firstly the asphaltenes were precipitated with n-heptane. Another portion was loaded on a silica column and eluted with solvents of increasing polarity. Four fractions 1, 2, 3 and 4 were separated. Oil in water emulsions were prepared for determination of Ni and V by ET-AAS. The analysis was carried out without chemical modifier (stable compounds) and with 20 µg Pd (Total Ni and V) and the volatile fraction was calculated by difference (Fig.1). Brandeo et al (2007) proposed a procedure for direct determination of Cu, Fe and V in petroleum samples by ET-AAS using a solid sampling accessory without any sample pretreatment or dilution. A Pd + Triton X-100 solution was used as chemical modifier. The limits of detection at the optimized conditions were 10, 200 and 800 pg for Cu, Fe and V respectively for sample masses ranging 0.10-3.0 mg. Aqueous calibrations were used for quantitation. Luz and Oliveira (2011) determined Cr, Fe, Ni and V in crude oil using emulsion sampling by ET-AAS. The emulsion was prepared in a mixture of n-hexane + Triton X-100, Mg(NO3)2 was used as chemical modifier. The reliability of the proposed method was checked by fuel oil standard reference material analysis. Dittert et al (2010) simultaneously determined Co and V in crude oils by high resolution continuum source ET-AAS, V and Co were determined at 240.674 nm and 240.725 nm. The samples were analyzed directly without dilution; Pd and Triton X-100 were added as chemical modifiers. Aqueous solutions were used for calibration. Two certified oil reference materials were analyzed and results were in agreement with certified and reported

values.

#### **3.2 Atomic absorption spectrometry**

#### **3.2.1 Flame Atomic Absorption Spectrometry (FAAS)**

FAAS indicates inherently low sensitivity for metal determinations and a few reports are available in the literature involving the direct analysis of crude oils by FAAS. A sufficiently large sample mass may compensate for lower FAAS sensitivity with longer analysis time. Platteau and Carriillo (1995) determined Fe, Na and Ni in crude oils by FAAS. Ni, V and Fe in crude oils and residual fuels have been determined by FAAS after ashing with H2SO4 (standard test methods ASTM 2005). Fabec and Ruschak (1985) determined Ni and V in crudes and heavy crude fraction by FAAS after dilution in xylene. Guidr and Sneddon (2002) determined V by nitrous oxide : acetylene flame AAS and (Hammond et al., 1998) analyzed Cd, Pb and Ni by FAAS in crudes and its burning residues after solublization in MIBK. Osibanjo et al (1984) determined Ni, Cu, Zn, Na, Pb, Cd and Fe by FAAS in petroleum crudes after dilution with toluene – acetic acid mixture. Calibration was performed with inorganic salts and by analyte addition. Sebor et al (1982) discussed FAAS analysis of crude oils using dilution methods with different solvents or solvent mixtures. Different organic compounds of the same element present different responses in the flame, no matter if an air or a nitrous oxide acetylene flame was used. This led to calibration difficulties as well different responses depending on the organometallic composition of the sample. De la Guardia and Lizondo (1993) determined Ni in fuel oil by FAAS using 4% v/v oil-in-water emulsion.

#### **3.2.2 Electrothermal Atomic Absorption Spectrometry (ET-AAS)**

ET-AAS with a graphite furnace is a useful analytical technique for metal analysis from crude oils, because of its high sensitivity and capability to deal with organic loads. In addition ET-AAS requires only small amount of sample. ET-AAS make possible direct analysis of crude oils, because it allows complete elimination of organic matrix, if an appropriate heating program and suitable chemical modifiers are used (das Graces Andrade Koren, 2007).

Turunen et al (1995) determined As, Cd, Cr, Cu, Mn, Ni, Pd and V in heavy oils by ET-AAS after acid digestion with HNO3-H2SO4 mixture. Alvarado et al (1990) analyzed Cr, Cu, Fe, Mn, Ni and V by ET-ASS after micro-wave digestion of various crude oil samples. Bruhn and Cabalin (1983) proposed determination of Ni in gas oil after dilution with xylene by ET-AAS, analyte addition was used for quantitation. Gonzalez et al (1987) determined V, Ni, Fe and Pb in crude and fuel oils following dilution with xylene and MIBK. The quantitation was by analyte addition calibration curves. Bermejo-Barrera (1991) determined V in petroleum samples by ET-AAS after dissolution in xylene. They proposed that the crude oil is diluted to the extent that matrix interference is eliminated. Thomainidis and Piperaki (1996) examined the behavior of a series of chemical modifiers for the determination of V in a water and oil matrix. In the determination of V in a multi-element standard diluted with MIBK, the addition of Pt as modifier enhanced the pyrolysis temperature from 1000 to 1400 oC with improvement in the sensitivity. Stigter et al (2000) determined Cd, Cr and Cu in crude oils by ET-AAS using Zeeman-effect background correction as well as oxygen ashing during the pyrolysis step. Finally they used mixture of toluene and acetic acid 4:1 v/v as a solvent for dissolution of the samples. Nakamoto et al (2004) determined V in heavy fuel oils

FAAS indicates inherently low sensitivity for metal determinations and a few reports are available in the literature involving the direct analysis of crude oils by FAAS. A sufficiently large sample mass may compensate for lower FAAS sensitivity with longer analysis time. Platteau and Carriillo (1995) determined Fe, Na and Ni in crude oils by FAAS. Ni, V and Fe in crude oils and residual fuels have been determined by FAAS after ashing with H2SO4 (standard test methods ASTM 2005). Fabec and Ruschak (1985) determined Ni and V in crudes and heavy crude fraction by FAAS after dilution in xylene. Guidr and Sneddon (2002) determined V by nitrous oxide : acetylene flame AAS and (Hammond et al., 1998) analyzed Cd, Pb and Ni by FAAS in crudes and its burning residues after solublization in MIBK. Osibanjo et al (1984) determined Ni, Cu, Zn, Na, Pb, Cd and Fe by FAAS in petroleum crudes after dilution with toluene – acetic acid mixture. Calibration was performed with inorganic salts and by analyte addition. Sebor et al (1982) discussed FAAS analysis of crude oils using dilution methods with different solvents or solvent mixtures. Different organic compounds of the same element present different responses in the flame, no matter if an air or a nitrous oxide acetylene flame was used. This led to calibration difficulties as well different responses depending on the organometallic composition of the sample. De la Guardia and Lizondo (1993) determined Ni in fuel oil by FAAS using 4% v/v

ET-AAS with a graphite furnace is a useful analytical technique for metal analysis from crude oils, because of its high sensitivity and capability to deal with organic loads. In addition ET-AAS requires only small amount of sample. ET-AAS make possible direct analysis of crude oils, because it allows complete elimination of organic matrix, if an appropriate heating program and suitable chemical modifiers are used (das Graces Andrade

Turunen et al (1995) determined As, Cd, Cr, Cu, Mn, Ni, Pd and V in heavy oils by ET-AAS after acid digestion with HNO3-H2SO4 mixture. Alvarado et al (1990) analyzed Cr, Cu, Fe, Mn, Ni and V by ET-ASS after micro-wave digestion of various crude oil samples. Bruhn and Cabalin (1983) proposed determination of Ni in gas oil after dilution with xylene by ET-AAS, analyte addition was used for quantitation. Gonzalez et al (1987) determined V, Ni, Fe and Pb in crude and fuel oils following dilution with xylene and MIBK. The quantitation was by analyte addition calibration curves. Bermejo-Barrera (1991) determined V in petroleum samples by ET-AAS after dissolution in xylene. They proposed that the crude oil is diluted to the extent that matrix interference is eliminated. Thomainidis and Piperaki (1996) examined the behavior of a series of chemical modifiers for the determination of V in a water and oil matrix. In the determination of V in a multi-element standard diluted with MIBK, the addition of Pt as modifier enhanced the pyrolysis temperature from 1000 to 1400 oC with improvement in the sensitivity. Stigter et al (2000) determined Cd, Cr and Cu in crude oils by ET-AAS using Zeeman-effect background correction as well as oxygen ashing during the pyrolysis step. Finally they used mixture of toluene and acetic acid 4:1 v/v as a solvent for dissolution of the samples. Nakamoto et al (2004) determined V in heavy fuel oils

**3.2 Atomic absorption spectrometry**

oil-in-water emulsion.

Koren, 2007).

**3.2.1 Flame Atomic Absorption Spectrometry (FAAS)**

**3.2.2 Electrothermal Atomic Absorption Spectrometry (ET-AAS)**

using tungsten coated graphite furnace. The effect of sulphur interference on the determination was examined. The sulphur content less than 1% can be tolerated. An agreement between proposed and comparative procedures was reported. Meeravali and Kumar (2001) analyzed Ni and V in naphtha and fuel oils after emulsion formation by ET-AAS using W-Ir as permanent modifier. The oil samples diluted in toluene was emulsified with 3% Triton X-100 in water. Calibration was performed with organometallic standards prepared in same manner. Burguera et al (2003) analyzed Cr in heavy crude oil and in bitumen in water emulsion by ET-AAS after sample emulsification. Vale et al (2004) optimized the determination of Ni in petroleum using both line source and high resolution continuum source ET-AAS. They stabilized sample and analyte solutions as an emulsion consisting of xylene, Triton X-100 and water. The authors observed a significant Ni loss at pyrolysis temperature of 500 oC, most probably due to the presence of volatile Ni species. However better results were reported at pyrolysis temperature of 400 oC. Aucelio et al (2004) determined V in the asphaltene petroleum fraction by ET-AAS. The solution of the sample was stabilized by mixing with 1-propanol and HNO3, forming detergentless microemulsion. Calibration was performed by spiking inorganic V in the same micro-emulsion medium. Damin et al (2005) determined Ni and V in oil samples by line source ET-AAS, Pd (20 µg) was used as chemical modifier. Good agreement was reported between found and expected values. Quadros et al (2010) determined Ni and V simultaneously as their total and nonvolatile fractions in crude oil samples using high resolution continuum source graphite atomic absorption spectrometry. Determination was carried out at 305.432 nm and 305.633 nm for Ni and V respectively using linear charge – coupled device array detection. Oil-inwater emulsions were used for crude oil sample preparation. Nitric acid was added to emulsion for the determination of total Ni and V concentration. In the absence of acid volatile fraction was lost in the pyrolysis and thermally stable fractions were determined. The concentration of the volatile fraction was obtained by difference. Vale et al (2006) used ET-AAS to differentiate between volatile and nonvolatile Ni and V compounds in crude oil. Two crude oil samples were separated in two steps: firstly the asphaltenes were precipitated with n-heptane. Another portion was loaded on a silica column and eluted with solvents of increasing polarity. Four fractions 1, 2, 3 and 4 were separated. Oil in water emulsions were prepared for determination of Ni and V by ET-AAS. The analysis was carried out without chemical modifier (stable compounds) and with 20 µg Pd (Total Ni and V) and the volatile fraction was calculated by difference (Fig.1). Brandeo et al (2007) proposed a procedure for direct determination of Cu, Fe and V in petroleum samples by ET-AAS using a solid sampling accessory without any sample pretreatment or dilution. A Pd + Triton X-100 solution was used as chemical modifier. The limits of detection at the optimized conditions were 10, 200 and 800 pg for Cu, Fe and V respectively for sample masses ranging 0.10-3.0 mg. Aqueous calibrations were used for quantitation. Luz and Oliveira (2011) determined Cr, Fe, Ni and V in crude oil using emulsion sampling by ET-AAS. The emulsion was prepared in a mixture of n-hexane + Triton X-100, Mg(NO3)2 was used as chemical modifier. The reliability of the proposed method was checked by fuel oil standard reference material analysis. Dittert et al (2010) simultaneously determined Co and V in crude oils by high resolution continuum source ET-AAS, V and Co were determined at 240.674 nm and 240.725 nm. The samples were analyzed directly without dilution; Pd and Triton X-100 were added as chemical modifiers. Aqueous solutions were used for calibration. Two certified oil reference materials were analyzed and results were in agreement with certified and reported values.

Determination of Metal Ions in Crude Oils 131

dessolvator, a thermostated condenser between the spray chamber and the plasma torch or a chilled spray chamber. Alternatively the sample is digested to obtain aqueous solutions

Botto (1993) and Botto and Zhu (1996) determined metal by ICP-OES in petroleum oils after dilution with organic solvents. Souza et al (2006) determined Mo, Zn, Cd, Ti, Ni, V, Fe, Mn, Cr and Co in crude oil by ICP-OES using detergentless emulsions comprising of acidified water for element solublization and propan-1-ol as a cosolvent with the addition of oxygen to the nebulizer gas flow. Fabec and Ruschak (1985) determined Ni and V in crudes and heavy crude fractions by ICP-OES after dilution in xylene. Mello et al (2009) determined Ni, V and S in crude oils distillation residues by ICP-OES after digestion of sample by microwave induced combustion. De Souza et al (2006) determined Mo, Cr, V and Ti in diesel and in used fuel oil by ICP-OES. Detergent and detergentless emulsion sample preparation procedures were evaluated and better results were obtained for detergent emulsions with recoveries ranging from 90.1-106.5%. Borszeki et al (1992) determined Al, Cr, Cu, Fe, Mg, Ni and Pb in oil and petroleum products by ICP-OES using a minitorch. The samples were prepared as aqueous emulsions. Quantitation was with aqueous standards and the results were in good agreement with those obtained using oil standard solutions. Brenner et al (1996) determined lead in gasoline by ICP-OES using argon and argon-oxygen as plasma

ICP-MS is highly sensitive multielement technique, but the introduction of organic solvents and the compounds in plasma requires special care similar to ICP-OES, because the organic load may destabilize or extinguish the plasma. ICP-MS encounters additional problems of formation of carbon deposit on the sampler and skimmer cone and in the ion lens of the mass spectrometer and spectral interferences owing to carbon based species (Lord et al., 1991), (Brenner et al., 1997). In ICP-MS spectral interferences may also occur as crude oil contains a number of elements at low concentrations (ng/g) levels (Tan and Horlick, 1986). The effect of polyatomic interferences may be minimized by the choice of alternate isotopes or the use of desolvation system to reduce the solvent load (Jakubowski et al., 1992). The problem of the deposition of carbon on the sampler and skimmer cone in ICP-MS was

Duyck et al (2002) determined Ag, Al, Ba, Cd, Co, Cu, Fe, La, Mg, Mo and Mn in residual fuel oil and crude oils by ICP-MS after dilution of the samples in toluene, using ultrasonic nebulization. Good accuracy was reported for the determinations of the metals. Wondimu et al (2000) analysed residual fuel oil for Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe and Hg by ICP-MS after micro-wave acid decomposition. H2O2 was used after acid decomposition for better carbon removal. Lord (1991) determined Li, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Mo, Ag, Cd, Sn, Sb, Ba and Pb in crude oils by ICP-MS with mciro-emulsion sample introduction. Kowalewska et al (2005) determined Cu in crude oils and crude oil distillation products by ICP-MS after ashing and micro-wave assisted decomposition of analyte and transferred to aqueous solution. Good recovery of Cu was reported. Kelly et al (2003) determined Hg in crude oils and refined products by cold Vapor ICP-MS after decomposition of the sample by closed system combustion. Botto (2002) analysed crude oil, petroleum naphthas and tars for Na, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Y, Mo, Cd, Sn, Sb,

**3.4 Inductively Coupled Plasma Mass Spectrometry (ICP-MS)**

decreased by the addition of O2 to the argon (Magyar (1986).

(Das Gragas Andrade Korn (2007).

gas.

Fig. 1. Absorbance spectrum for the OB-2 crude oil sample emulsion in the vicinity of the vanadium secondary line at 305.633nm, with a pyrolysis temperature of 1000 °C, Wavelength resolved integrated absorbance spectrum (Quadros et al. 2010) with permission.

#### **3.2.3 Chemical vapour generation AAS**

The elements Hg, As and Sb are present in the fuels at low concentrations and chemical vapour generation (CVG) technique can be applied to provide required sensitivity. However CVG when applied to crude oils is susceptible to spectral interference from aromatic organic compounds in the gas stream. Cold vapour (CV) technique for mercury and hydride generation (HG) technique for As & Sb requires the analyte to be present in inorganic form in a defined oxidation state. Therefore the applications of CVG to the analysis of fuels generally requires complete mineralization of the metal-organic compounds and separation from organic phase (das Gracas Andrade Korn, 2007). Campbell and Karnel (1992) determined As, Sb and Se in oil waters by hydride generation AAS, after complete oxidation of the organic matrix using microwave-assisted digestion in the closed system. Puri and Irgolic (1989) determined As in crude oils after extraction of As in boiling aqueous nitric acid, followed by mineralization of the extract with concentrated HNO3/H2SO4 and reduction of arsenate to arsine in hydride generator. Wilhelm and Bloom (2000) have reviewed mercury in petroleum and have described the use of cold vapour AAS for sensitive detection of mercury.

#### **3.3 Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)**

ICP-OES has the advantage of multi-elemental detection capability and offers a wide linear dynamic range. However, the introduction of organic solvents, such as fuels cause plasma destabilization or even plasma extinction and the use of ICP accessories may be necessary, such as direct injection nebulizer, ultrasonic nebulizer with micro-porous membrane

Fig. 1. Absorbance spectrum for the OB-2 crude oil sample emulsion in the vicinity of the

Wavelength resolved integrated absorbance spectrum (Quadros et al. 2010) with permission.

The elements Hg, As and Sb are present in the fuels at low concentrations and chemical vapour generation (CVG) technique can be applied to provide required sensitivity. However CVG when applied to crude oils is susceptible to spectral interference from aromatic organic compounds in the gas stream. Cold vapour (CV) technique for mercury and hydride generation (HG) technique for As & Sb requires the analyte to be present in inorganic form in a defined oxidation state. Therefore the applications of CVG to the analysis of fuels generally requires complete mineralization of the metal-organic compounds and separation from organic phase (das Gracas Andrade Korn, 2007). Campbell and Karnel (1992) determined As, Sb and Se in oil waters by hydride generation AAS, after complete oxidation of the organic matrix using microwave-assisted digestion in the closed system. Puri and Irgolic (1989) determined As in crude oils after extraction of As in boiling aqueous nitric acid, followed by mineralization of the extract with concentrated HNO3/H2SO4 and reduction of arsenate to arsine in hydride generator. Wilhelm and Bloom (2000) have reviewed mercury in petroleum and have described the use of cold vapour AAS for

vanadium secondary line at 305.633nm, with a pyrolysis temperature of 1000 °C,

**3.3 Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)**

ICP-OES has the advantage of multi-elemental detection capability and offers a wide linear dynamic range. However, the introduction of organic solvents, such as fuels cause plasma destabilization or even plasma extinction and the use of ICP accessories may be necessary, such as direct injection nebulizer, ultrasonic nebulizer with micro-porous membrane

**3.2.3 Chemical vapour generation AAS**

sensitive detection of mercury.

dessolvator, a thermostated condenser between the spray chamber and the plasma torch or a chilled spray chamber. Alternatively the sample is digested to obtain aqueous solutions (Das Gragas Andrade Korn (2007).

Botto (1993) and Botto and Zhu (1996) determined metal by ICP-OES in petroleum oils after dilution with organic solvents. Souza et al (2006) determined Mo, Zn, Cd, Ti, Ni, V, Fe, Mn, Cr and Co in crude oil by ICP-OES using detergentless emulsions comprising of acidified water for element solublization and propan-1-ol as a cosolvent with the addition of oxygen to the nebulizer gas flow. Fabec and Ruschak (1985) determined Ni and V in crudes and heavy crude fractions by ICP-OES after dilution in xylene. Mello et al (2009) determined Ni, V and S in crude oils distillation residues by ICP-OES after digestion of sample by microwave induced combustion. De Souza et al (2006) determined Mo, Cr, V and Ti in diesel and in used fuel oil by ICP-OES. Detergent and detergentless emulsion sample preparation procedures were evaluated and better results were obtained for detergent emulsions with recoveries ranging from 90.1-106.5%. Borszeki et al (1992) determined Al, Cr, Cu, Fe, Mg, Ni and Pb in oil and petroleum products by ICP-OES using a minitorch. The samples were prepared as aqueous emulsions. Quantitation was with aqueous standards and the results were in good agreement with those obtained using oil standard solutions. Brenner et al (1996) determined lead in gasoline by ICP-OES using argon and argon-oxygen as plasma gas.

#### **3.4 Inductively Coupled Plasma Mass Spectrometry (ICP-MS)**

ICP-MS is highly sensitive multielement technique, but the introduction of organic solvents and the compounds in plasma requires special care similar to ICP-OES, because the organic load may destabilize or extinguish the plasma. ICP-MS encounters additional problems of formation of carbon deposit on the sampler and skimmer cone and in the ion lens of the mass spectrometer and spectral interferences owing to carbon based species (Lord et al., 1991), (Brenner et al., 1997). In ICP-MS spectral interferences may also occur as crude oil contains a number of elements at low concentrations (ng/g) levels (Tan and Horlick, 1986). The effect of polyatomic interferences may be minimized by the choice of alternate isotopes or the use of desolvation system to reduce the solvent load (Jakubowski et al., 1992). The problem of the deposition of carbon on the sampler and skimmer cone in ICP-MS was decreased by the addition of O2 to the argon (Magyar (1986).

Duyck et al (2002) determined Ag, Al, Ba, Cd, Co, Cu, Fe, La, Mg, Mo and Mn in residual fuel oil and crude oils by ICP-MS after dilution of the samples in toluene, using ultrasonic nebulization. Good accuracy was reported for the determinations of the metals. Wondimu et al (2000) analysed residual fuel oil for Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe and Hg by ICP-MS after micro-wave acid decomposition. H2O2 was used after acid decomposition for better carbon removal. Lord (1991) determined Li, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Mo, Ag, Cd, Sn, Sb, Ba and Pb in crude oils by ICP-MS with mciro-emulsion sample introduction. Kowalewska et al (2005) determined Cu in crude oils and crude oil distillation products by ICP-MS after ashing and micro-wave assisted decomposition of analyte and transferred to aqueous solution. Good recovery of Cu was reported. Kelly et al (2003) determined Hg in crude oils and refined products by cold Vapor ICP-MS after decomposition of the sample by closed system combustion. Botto (2002) analysed crude oil, petroleum naphthas and tars for Na, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Y, Mo, Cd, Sn, Sb,

Determination of Metal Ions in Crude Oils 133

fields were analyzed for metal contents. Caumette et al (2010) coupled size exclusion chromatography (SEC) and normal phase (NP) HPLC with ICP-MS and investigated molecular distribution of Ni and V in crude oils. The metal species in SEC fractions were reported to be sufficiently stable to be collected and preconcentrated to allow the development of a bidimensional chromatography SEC-NP-HPLC –ICP-MS for the probing of the metal distribution in crude oils in terms of molecular weight and polarity. Ellis et al (2011) coupled GC with ICP-MS for the determination of Ni and V in crude oils and its fractions. The method required a transfer line and ICP injector heated at 350 oC for rapid transfer of separated species from GC to the ICP-MS in heated argon gas. Ni and V determination was carried out in different crude oils. Mirza et al (2009) reported the determination of Fe. Co, Ni and V from crude petroleum oil samples after chelation with bis(salicylaldehyde) tetramethylethylenediimine by miceller electrokinetic chromatography (MEKC). Uncoated fused silica capillary was used with an applied voltage of 30 kV with photodiode array detection at 228 nm. SDS was added as miceller medium at pH 8.2 with sodium tetraborate buffer (0.1M). The determinations of Fe, Cu, Co, Ni and V in crude petroleum oils were reported with RSD within 1.1-4.1% (n=3) (Fig.2). Zeng and Uden (1994) used high temperature GC coupled with micro-wave induced plasma atomic emission for the determination of V, Ni and Fe

Fig. 2. Analysis of crude oil sample (1) H2SA2Ten, (2) Co(II), (3) V(IV), (4) Fe(II), and (5) Ni(II), as chelates of H2SA2Ten., on uncoated silica capillary with total length 50 cm and effective length 38.8 cm with 75 µm id at 25°C. Run buffer tetraborate (0.1 M), SDS (0.04 M) 3:1 v/v, voltage 30 kV, pH 8.2, and photodiode array detection at 228 nm (Mirza et al 2009)

porphyrins in crude oils.

with permission.

Hg, Pb and Bi by ICP-MS using direct injection technique after the dilution of the samples in xylene. Al-Swaidan (1996) determined Pb, Ni and V in crude oil by coupling sequential injection with ICP-MS. A microemulsion crude oil sampling procedure was used. The quantitation was by standard addition technique using oil soluble organometallic elements. Pecira et al (2010) analyzed light and heavy crude oil for the determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Ti, V and Zn by ICP-MS after microwave induced combustion in closed vessel. Akinlua et al (2008) determined rare earth elements of crude oil from the offshore-shallow water and onshore fields in the Niger delta by ICP-MS. The samples were prepared by acid digestion into colourless aqueous solutions. The concentrations of the detected elements La, Ce, Pr, Nb, Sm, Eu, Gd, Dy, Er and Yb ranged from 0.01-1.58 µg/L with an average of 0.98 µg/L (% RSD < 5).

#### **3.5 Chromatographic techniques**

Chromatography is a separation technique and has been used for the determination of metal ions in crude oils. The methods are based on determination of total metal ions, after complete mineralization of the crude oil or as metalloporphyrins using hyphenated techniques..

Quimby et al (1991) described selective detection of volatile Ni, V and Fe metalloporphyrins in crude oil samples. Gas chromatography connected with an atomic emission detector (AED) was used for the simultaneous detection of Ni 301.2 nm, V 292.4 nm and Fe 302.1 nm. Detection limit for these metals ranged from 0.05-5 pg/sec. The presence of volatile forms of these metals in several crude oil samples was confirmed.

Les Ebdon et al (1994) examined high temperature gas chromatography (HTGC) and high performance liquid chromatography (HPLC) coupled to ICP-MS for the determination of geoporphyrins from crude oil. HTGC-ICP-MS was used for rapid identification of Co, Cr, Fe, Ni, Ti, V and Zn metalloporphyrins. Quantitative data was obtained by HPLC-ICP-MS and HPLC with UV absorption detector. Levels of Ni geoporphyrins were in the range 15-20 ug/g. Khuhawar et al (1996) determined V in crude petroleum oils from lower Indus basin oil fields by GC after wet acid digestion. Tetradentate ligand bis(trifluoroacetylacetone)dl-stilbenediimine was used as chelating reagent for elution from GC column BP-1. Khuhawar and Arain (2006) reported liquid chromatographic method for the determination of V in the petroleum oils using 2 acetylpyridine-4-phenyl-3-thiosemicarbazone as derivatizing reagent from Kromasil 100 C-18 column. The vanadium contents were reported 0.32-2.3 ug/g with RSD 1.5-4.5%. Khuhawar et al reported normal phase HPLC procedure for the determination of V from crude petroleum oils using bis(salicylaldehyde) tetramethylethylenediimine as complexing reagent. The V contents in petroleum oils were reported 0.47-0.54 ug/g. Amoil et al (2006) analyzed V, Ni. Fe and Cu by HPLC using 10 cm reversed phase HPLC column. The metals were extracted with 8-hydroxyquinoline from acidic medium. The recoveries of metal ions were reported within 85-99% with HPLC separation time less than 4 min. Khuhawar and Lanjwani (1996) described simultaneous HPLC determination of Cu, Fe, Ni and V in crude petroleum oils based on pre-column complexation of analytes by bis(acetylpivalylmethane)ethylenediimine, followed by solvent extraction and HPLC separation on a reversed phase C-18 column with UV detection at 260 nm. The crude petroleum oils collected from the Indus south basin oil

Hg, Pb and Bi by ICP-MS using direct injection technique after the dilution of the samples in xylene. Al-Swaidan (1996) determined Pb, Ni and V in crude oil by coupling sequential injection with ICP-MS. A microemulsion crude oil sampling procedure was used. The quantitation was by standard addition technique using oil soluble organometallic elements. Pecira et al (2010) analyzed light and heavy crude oil for the determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Ti, V and Zn by ICP-MS after microwave induced combustion in closed vessel. Akinlua et al (2008) determined rare earth elements of crude oil from the offshore-shallow water and onshore fields in the Niger delta by ICP-MS. The samples were prepared by acid digestion into colourless aqueous solutions. The concentrations of the detected elements La, Ce, Pr, Nb, Sm, Eu, Gd, Dy, Er and Yb

Chromatography is a separation technique and has been used for the determination of metal ions in crude oils. The methods are based on determination of total metal ions, after complete mineralization of the crude oil or as metalloporphyrins using hyphenated

Quimby et al (1991) described selective detection of volatile Ni, V and Fe metalloporphyrins in crude oil samples. Gas chromatography connected with an atomic emission detector (AED) was used for the simultaneous detection of Ni 301.2 nm, V 292.4 nm and Fe 302.1 nm. Detection limit for these metals ranged from 0.05-5 pg/sec. The presence of volatile forms of

Les Ebdon et al (1994) examined high temperature gas chromatography (HTGC) and high performance liquid chromatography (HPLC) coupled to ICP-MS for the determination of geoporphyrins from crude oil. HTGC-ICP-MS was used for rapid identification of Co, Cr, Fe, Ni, Ti, V and Zn metalloporphyrins. Quantitative data was obtained by HPLC-ICP-MS and HPLC with UV absorption detector. Levels of Ni geoporphyrins were in the range 15-20 ug/g. Khuhawar et al (1996) determined V in crude petroleum oils from lower Indus basin oil fields by GC after wet acid digestion. Tetradentate ligand bis(trifluoroacetylacetone)dl-stilbenediimine was used as chelating reagent for elution from GC column BP-1. Khuhawar and Arain (2006) reported liquid chromatographic method for the determination of V in the petroleum oils using 2 acetylpyridine-4-phenyl-3-thiosemicarbazone as derivatizing reagent from Kromasil 100 C-18 column. The vanadium contents were reported 0.32-2.3 ug/g with RSD 1.5-4.5%. Khuhawar et al reported normal phase HPLC procedure for the determination of V from crude petroleum oils using bis(salicylaldehyde) tetramethylethylenediimine as complexing reagent. The V contents in petroleum oils were reported 0.47-0.54 ug/g. Amoil et al (2006) analyzed V, Ni. Fe and Cu by HPLC using 10 cm reversed phase HPLC column. The metals were extracted with 8-hydroxyquinoline from acidic medium. The recoveries of metal ions were reported within 85-99% with HPLC separation time less than 4 min. Khuhawar and Lanjwani (1996) described simultaneous HPLC determination of Cu, Fe, Ni and V in crude petroleum oils based on pre-column complexation of analytes by bis(acetylpivalylmethane)ethylenediimine, followed by solvent extraction and HPLC separation on a reversed phase C-18 column with UV detection at 260 nm. The crude petroleum oils collected from the Indus south basin oil

ranged from 0.01-1.58 µg/L with an average of 0.98 µg/L (% RSD < 5).

these metals in several crude oil samples was confirmed.

**3.5 Chromatographic techniques**

techniques..

fields were analyzed for metal contents. Caumette et al (2010) coupled size exclusion chromatography (SEC) and normal phase (NP) HPLC with ICP-MS and investigated molecular distribution of Ni and V in crude oils. The metal species in SEC fractions were reported to be sufficiently stable to be collected and preconcentrated to allow the development of a bidimensional chromatography SEC-NP-HPLC –ICP-MS for the probing of the metal distribution in crude oils in terms of molecular weight and polarity. Ellis et al (2011) coupled GC with ICP-MS for the determination of Ni and V in crude oils and its fractions. The method required a transfer line and ICP injector heated at 350 oC for rapid transfer of separated species from GC to the ICP-MS in heated argon gas. Ni and V determination was carried out in different crude oils. Mirza et al (2009) reported the determination of Fe. Co, Ni and V from crude petroleum oil samples after chelation with bis(salicylaldehyde) tetramethylethylenediimine by miceller electrokinetic chromatography (MEKC). Uncoated fused silica capillary was used with an applied voltage of 30 kV with photodiode array detection at 228 nm. SDS was added as miceller medium at pH 8.2 with sodium tetraborate buffer (0.1M). The determinations of Fe, Cu, Co, Ni and V in crude petroleum oils were reported with RSD within 1.1-4.1% (n=3) (Fig.2). Zeng and Uden (1994) used high temperature GC coupled with micro-wave induced plasma atomic emission for the determination of V, Ni and Fe porphyrins in crude oils.

Fig. 2. Analysis of crude oil sample (1) H2SA2Ten, (2) Co(II), (3) V(IV), (4) Fe(II), and (5) Ni(II), as chelates of H2SA2Ten., on uncoated silica capillary with total length 50 cm and effective length 38.8 cm with 75 µm id at 25°C. Run buffer tetraborate (0.1 M), SDS (0.04 M) 3:1 v/v, voltage 30 kV, pH 8.2, and photodiode array detection at 228 nm (Mirza et al 2009) with permission.

Determination of Metal Ions in Crude Oils 135

than direct sample introduction after dilution. Sample dilution is attractive because of its simplicity, but complete solublization may be difficult due to the complex nature of the crude oil. The concentration of the diluted solution may change rapidly due to the adsorption on the walls of the container. Alternatively dilution with the three component system (emulsions and micro emulsions) are reported to provide better precision and accuracy of results. The use of aqueous standards for calibration is an added advantage. Electrothermal AAS with graphite furnace atomizer and ICP-MS appear to be more sensitive techniques. In case of ET-AAS stabilization of volatile compounds during pyrolysis step must be considered. The use of appropriate modifier, even for the element known as a nonvolatile may be necessary. ICP-MS requires periodic cleaning of lens, sampler and skimmer due to carbon build up. Polyatomic interferences in quadruple ICP-MS must also be considered. Metal speciation using hyphenated techniques has important place in oil

Ackley, K.L., Day, J.A., Caruso, J.A., (2005), Separation of metalloporphyrins by capillary

Akinlu, A, Smith, M.S. (2010), Supercritical water extraction of trace metals from petroleum

Akinlua, A., Ajayi, T.R., Adeleke, B.B., (2007), Organic and inorganic geochemistry of

Akinlua, H., Torto, N., Ajayi, T.R., (2008), Determination of rare earth elements in Nigar

Alberdi-Genolet, M., Tocco, R., (1999), Trace metals and organic geochemistry of the

Al-Shahristani, H., Al-Atya, M.J., (1972), Vertical migration of oil in Iraqi oil fields: Evidence

Al-Swaidan, H.M. (1996), The determination of lead, nickel and vanadium in Saudi Arabian

Alvarado, J., Picon, A.R., de Vecchi, C.M., (1990), Microwave wet acid digestion in the

Amoli, H.S., Porgam, A., Sadr, Z.B., Mohanazadeh, F., (2006), Analysis of metal ions in

Amorin, F.A.C., Welz, B., Costa, A.C.S., Lepri, F.G., Vale, S.L.C., Ferreira, M.G.R.., (2007),

Andersen, S.I., Keul, A., Stenby .E., (1997), Variation in composition of sub fractions of

spectrometric detection, *J. Chromatogr. A.*, 888, 293-298.

Northwestern Niger delta oils, *Geochem. J.* , 41, 271-281.

Campanian), Venezuela,*Chem. Geol*. 160, 19-38.

spectrometry, *Talanta*, 43, 1313-1319.

column, *J. Chromatogr, A.*, 1118, 82-84.

spectroscopic techniques, *Talanta*, 72, 349-359.

petroleum asphaltenes, *Pet. Sci. Technol*. 15, 611-645.

electrophoresis with UV detection and inductively coupled plasma mass

delta crude oil by inductively coupled plasma-mass spectrometry, *Fuel*,87, 1469-

Machiques Member (Aptian–Albian) and La Luna Formation (Cenomanian–

based on vanadium and nickel concentrations, *Geochim. Cosmochina Acta*, 36, 929-

crude oil by sequential injection analysis inductively coupled plasma mass

preparation of crude oil samples for AAS determination of their chromium, copper, iron manganese, sodium, nickel, vanadium and zinc contents, *Acta Chim. Ven*. 41,

crude oils by revered phase high performance liquid chromatography using short

Determination of vanadium in petroleum and petroleum products using atomic

analysis for less explored crude oils and resins.

source rock, *Talanta*, 81, 1346-1349.

**5. References**

1477.

938.

306-319.

#### **3.6 Other techniques**

Other techniques can be used, but they are not widely reported. Gondal et al (2006) examined laser induced breakdown spectroscopy (LIBS) for the analysis of Ca, Fe, Mg, Cu, Zn, Na, Ni, K and Mo from Arabian crude oil residue samples. The dependence of time delay and laser beam energy on the elemental spectra was investigated. Quantitation was carried out by calibration of LIBS system with standard samples containing these trace elements. Mumoz et al (2007) examined electroanalytical stripping techniques for determination of Cu, Pb, Hg and Zn from crude oil and petroleum based fuels. The samples were decomposed by different microwave ovens before determinations. Square-wave stripping voltametry (SWSW) and stripping chromopotentiometry (SCP) at gold film electrodes were applied for Cu, Pb and Hg. Potentiometric stripping analysis (PSA) at mercury film electrodes was applied for Cu, Pb and Zn. SCP presented higher sensitivity for Cu and Hg at gold electrodes. PSA at mercury electrodes was preferred for Pb and Zn determinations. Xu et al (2005) extracted Ni and V petroporphyrins from Chinese heavy crude oils and then purified by silica gel chromatography. The extraction and purification were monitored using ultraviolet visible spectroscopy and the total petroporphyrins were analyzed using laser desorption ionization coupled with time of flight mass spectrometry. Yang et al (2003) determined Fe, Cu, Zn and Pb of engine oil by mild acid digestion and energy dispersive X-ray fluorescence spectrometry. A small aliquot (0.5 ml) of the acid digested sample was spotted onto a C-18 solid phase and then analyzed directly by X-ray fluorescence spectrometry.

#### **3.7 Speciation of metal ions**

Speciation studies are also directed towards isolation and identification of elements in different forms in crude oils. More is reported on V and Ni species. In majority of these studies focus has been the organometallic forms. The information may be of help in development of metal removal methods and in understanding the molecular environment associated in crude oils. The hyphenated HPLC and GC with ICP-MS, ICP-OES, and AAS have been examined (Les Ebdon et al., 1994), (Kumar et al., 1994), (Fish and Komlenic, 1984), (Fish et al., 1984), (Tao et al.,1998) for speciation studies of V, Ni and Hg in heavy crude petroleum, asphaltenes and natural gas condensates. Margueza et al (1999) used FAAS in comparison of three analytical methods to isolate and characterize V and Ni porphyrin from heavy crude oils. Lepri et al (2006) have carried out speciation analysis of volatile and nonvolatile vanadium compounds using high resolution continuum source atomic absorption spectrometry with a graphite furnace, taking advantage of higher volatility of the vanedyl porphyrin complexes, compared to nonporphyrins. Ackley et al (2005) examined capillary electrophoresis for the separation of metalloporphyrins, however the separation was limited to ionizable metalloporphyrins (with COOH functional group).

#### **4. Conclusion**

A significant improvement in the analytical instrumentation has been observed during last decade which has enabled to improve the sensitivity and selectivity of the determinations. The choice of the methodology for the determination of elements should be based on the matrix, the elements to be determined and the equipment available. Sample decomposition by wet digestion, preferably with microwave assisted heating is more robust and accurate than direct sample introduction after dilution. Sample dilution is attractive because of its simplicity, but complete solublization may be difficult due to the complex nature of the crude oil. The concentration of the diluted solution may change rapidly due to the adsorption on the walls of the container. Alternatively dilution with the three component system (emulsions and micro emulsions) are reported to provide better precision and accuracy of results. The use of aqueous standards for calibration is an added advantage. Electrothermal AAS with graphite furnace atomizer and ICP-MS appear to be more sensitive techniques. In case of ET-AAS stabilization of volatile compounds during pyrolysis step must be considered. The use of appropriate modifier, even for the element known as a nonvolatile may be necessary. ICP-MS requires periodic cleaning of lens, sampler and skimmer due to carbon build up. Polyatomic interferences in quadruple ICP-MS must also be considered. Metal speciation using hyphenated techniques has important place in oil analysis for less explored crude oils and resins.

#### **5. References**

134 Crude Oil Emulsions – Composition Stability and Characterization

Other techniques can be used, but they are not widely reported. Gondal et al (2006) examined laser induced breakdown spectroscopy (LIBS) for the analysis of Ca, Fe, Mg, Cu, Zn, Na, Ni, K and Mo from Arabian crude oil residue samples. The dependence of time delay and laser beam energy on the elemental spectra was investigated. Quantitation was carried out by calibration of LIBS system with standard samples containing these trace elements. Mumoz et al (2007) examined electroanalytical stripping techniques for determination of Cu, Pb, Hg and Zn from crude oil and petroleum based fuels. The samples were decomposed by different microwave ovens before determinations. Square-wave stripping voltametry (SWSW) and stripping chromopotentiometry (SCP) at gold film electrodes were applied for Cu, Pb and Hg. Potentiometric stripping analysis (PSA) at mercury film electrodes was applied for Cu, Pb and Zn. SCP presented higher sensitivity for Cu and Hg at gold electrodes. PSA at mercury electrodes was preferred for Pb and Zn determinations. Xu et al (2005) extracted Ni and V petroporphyrins from Chinese heavy crude oils and then purified by silica gel chromatography. The extraction and purification were monitored using ultraviolet visible spectroscopy and the total petroporphyrins were analyzed using laser desorption ionization coupled with time of flight mass spectrometry. Yang et al (2003) determined Fe, Cu, Zn and Pb of engine oil by mild acid digestion and energy dispersive X-ray fluorescence spectrometry. A small aliquot (0.5 ml) of the acid digested sample was spotted onto a C-18 solid phase and then analyzed directly by X-ray

Speciation studies are also directed towards isolation and identification of elements in different forms in crude oils. More is reported on V and Ni species. In majority of these studies focus has been the organometallic forms. The information may be of help in development of metal removal methods and in understanding the molecular environment associated in crude oils. The hyphenated HPLC and GC with ICP-MS, ICP-OES, and AAS have been examined (Les Ebdon et al., 1994), (Kumar et al., 1994), (Fish and Komlenic, 1984), (Fish et al., 1984), (Tao et al.,1998) for speciation studies of V, Ni and Hg in heavy crude petroleum, asphaltenes and natural gas condensates. Margueza et al (1999) used FAAS in comparison of three analytical methods to isolate and characterize V and Ni porphyrin from heavy crude oils. Lepri et al (2006) have carried out speciation analysis of volatile and nonvolatile vanadium compounds using high resolution continuum source atomic absorption spectrometry with a graphite furnace, taking advantage of higher volatility of the vanedyl porphyrin complexes, compared to nonporphyrins. Ackley et al (2005) examined capillary electrophoresis for the separation of metalloporphyrins, however the separation

A significant improvement in the analytical instrumentation has been observed during last decade which has enabled to improve the sensitivity and selectivity of the determinations. The choice of the methodology for the determination of elements should be based on the matrix, the elements to be determined and the equipment available. Sample decomposition by wet digestion, preferably with microwave assisted heating is more robust and accurate

was limited to ionizable metalloporphyrins (with COOH functional group).

**3.6 Other techniques**

fluorescence spectrometry.

**4. Conclusion**

**3.7 Speciation of metal ions**

Determination of Metal Ions in Crude Oils 137

Botto, R.I., (1993), Applications of ultrasonic neublization in the analysis of petroleum

Botto, R.I., Zhu, J., (1996), Universal calibration for analysis of organic solution by

Brandao, G.P., Camps, R.C., de Castro, E.V.R., de Jenus, H.C., (2006), Direct determination of

Brandas, G.P., de Campos, R.C., de Castro; E.V.R., de Jesus H.C. (2007), Direct determination

Brenner, I.B., Zander, A., Plantz, M., Zhu, J., (1997), Characterization of an ultrasonic

Bruhn, C.F., Cabalin, V.G., (1983), Direct determination of nickel in gas oil by atomic

Burguera, J.L., Avila-Gomez, R.M., Burgera, M., de Salaguer, R.A., Salaguer, J.L., Bracho,

Cardarelli, E., Cifani, M., Mecozzi, M., Sechi, G., (1986), Analytical application of emulsions:

Caumette, G., Lienemann, C.P. Merdrignae, I., Bouyssiere, B., Lobinski, R., (2010),

Choudhry, G.G., (1983), Humic substances: Sorptive interactions with environmental

Damin, I.C.F., Vale, M.G.R., Silva, M.M., Welz, B., Lepri, F.G., Santos, W.N.I., Ferricira, M.,

das Gracas Andrade Korn, M., Sodre dos Santos, D.S., Welz, B., Rodrigues Vale, M.G.,

atomic absorption spectrometry, *Spectrochim. Acta*, Part B, 62, 962-969. Brener, I.B., Zander, A., Kim, S. Shkolnik, J., (1996), Direct determination of lead in gasoline

atomic emission spectrometry*, J. Anal. Atom. Spectrom*. 11, 91-97.

spectrometry, *Anal. Bioanal. Chem*. 386, 2249-2253.

*Anal. At. Spectrom*. 8, 51-57.

*At. Spectrom*. 12, 273-279.

emulsion, *Talanta*, 61, 353-361.

chemicals ,*Toxicol. Envir. Chem*. 6, 127-171.

spectrometry. *J. Anal. At. Spectrom*. 20, 1332-1336.

*Talanta*, 33, 279-280.

review, *Talanta*, 73, 1-11.

25, 1123-1129.

675-681.

193-203.

petrochemical by inductively coupled plasma atomic emission spectrometry, *J.*

inductively coupled plasma atomic emission spectrometry, *J. Anal. At. Spectrom*. 11,

nickel in petroleum by solid sampling-graphite furnace atomic absorption

of copper, iron and vanadium in petroleum by solid sampling graphite furnace

using emulsification and argon and argon–oxygen inductively coupled plasma

nebulizer – member separation interface with inductively coupled plasma mass spectrometry for the determination of trace elements by solvent extraction, *J. Anal.*

absorption spectrometry with electrothermal atomization, *Anal. Chim. Acta*, 143,

C.L., Burguera-Pascu, M., Burguera-Pascu, C., Brunetto, R., Gallignani, M., de Pena, Y.P., (2003), Optimum phase-behavior formulation of surfactant oil/water system for the determination of chromium in heavy crude oil and in bitumen in water

Determination of lead in gasoline by atomic-absorption spectrophotometry,

Fractionation and speciation of nickel and vanadium in crude oils by size exclusion chromatography ICP-MS and normal phase HPLC-ICP-MS*, J. Anal. At. Spectrom*.

(2005), Palladium as chemical modifier for the stabilization of volatile nickel and vanadium compounds in crude oil using graphite furnace atomic absorption

Teixeira, A.P., de Castrolima, D., Ferreira, S.L.C., (2007), Atomic spectrometric methods for the determination of metals and metalloids in automotive fuels. A

*Annual Book of ASTM Standard*, ATSM-D5863 (2000), Standard test method for determination

*Annual Book of ATSM Standard*, ASTM-D5708 (2002), Standard test method for determination

*Annual Book of ATSM Standard*, ASTM-D5863-00A (2005), Method for determination nickel,

Anselmi, A., Tittarelli, P., Katskov, D.A., (2002), Determination of trace elements in

Aske, N., Hallevik, H., Sjoblom, J., (2001), Determination of Saturate, Aromatic, Resin, and

Aucelio, R.Q., Doyle, A., Pizzorano, B.S., Tristao, M.L.B., Campos, R.C., (2004),

Baker, E.W., Louda, J.W., (1986), Porphyrin geochemistry of Atlantic Jurassic-Cretaceous

Ball, J.S., Wenger, W.J., Hyden, H.J., Horr, C.A., Myers, A.T., (1960), Metal content of

Barwise, A.J.G., (1987), Mechanisms involved in altering Deoxophylloerythroetioporphyrin-

Barwise, A.J.G., (1990), Role of nickel and vanadium in petroleum classification , *Energy Fuel*,

Barwise, A.J.G., Roberts, I., (1984), Diagenetic and catagenetic pathways for porphyrins in

Bermejo-Barrera, P., Pita-Calvo, C., Bermejo-Marinez, F., (1991), Simple preparation

Borszeki, J., Knapp, G., Halmos, P., Bartha, L., (1992), Sample preparation procedure for the

Botto, R,I., (2002), Trace element analysis of petroleum naphthas and tars using direct

minitorch using emulsions, *Microchim. Acta*, 108, 157-161.

injection ICP-MS, *Can. J. Anal. Sci. Spectrosc.* 47, 1-13.

spectrometry with electrothemal atomization, *Anal. Lett*., 24, 447-458. Bethinetti, M., Spezia, S., Baroni, U., Bizzarri, G. (1995), Determination of trace elements in

Conshohockm, PA.

Conshohockm, PA.

Part B. 57, 403-411.

*Microchem. J.* 78, 21-26.

4, 647-652.

812.

and Materials, West Conshohockm, PA.

Infrared Spectroscopy, *Energy Fuels*, 15, 1304-1312.

black shales , *Adv. Organic Geochem*. 10, 905-914.

sediments, *Organic Geochem*. 6, 167-176.

twenty-four petroleums*, J. Chem. Eng. Data* 5, 553-557.

of nickel, vanadium, iron and sodium in crude oils and residual fuels by flame atomic absorption spectrometry, American Society for Testing and Materials, West

of nickel, vanadium and iron in crude oils and residual fuels by inductively coupled plasma (ICP) atomic emission spectrometry, American Society for Testing

vanadium, iron and sodium in crude oils and residual fuels by flame atomic absorption spectrometry, American Society for Testing and Materials, West

automotive fuels by filter furnace atomic absorption spectrometry *Spectrochim. Acta*

Asphaltenic (SARA) components in crude oils by means of infrared and Near-

Electrothermal atomic absorption spectrometric method for the determination of vanadium in diesel and asphaltene prepared as detergentless micro-emulsions,

Etioporphyrin ratios in sediments and oils, *J. Am. Chem. Soc. Spec. Pub.* 344, 100-109.

procedures for vanadium determination in petroleum by atomic absorption

fuel oils by inductively coupled plasma mass spectrometry after acid mineralization of sample in microwave oven, *J. Anal. At. Spectrom*., 10, 555-560. Bettinelli, M., Tittarelli, P., (1994), Evaluation and validation of Instrumental procedures for

the determination of nickel and vanadium in fuel oils, *J. Anal. At. Spectrom*. 9, 805-

determination of sulphur and trace metals in oil products by the ICP with a

Determination of Metal Ions in Crude Oils 139

Fabec, J.L., Ruschak, M.L., (1985), Determination of nickel, vanadium and sulphur in crude

Fan, T.G., Buckley, J.S., (2002), Rapid and accurate SARA analysis of medium gravity crude

Fish, R.H., Komlenic, J.J., (1984), Molecular characterization and profile identification of

Fish, R.H., Komlenic, J.J., Wines, B.K. (1984) Characterization and comparison of vanadyl

Gondal, M.A., Hussain, Y., Baig, M.A., (2006), Detection of heavy metal in Arabian crude oils residue using laser induced breakdown spectroscopy, *Talanta*, 69, 1072-1078. Gonzarez, M.C., Rodriguez, A.R., Gonzalez. V., (1987), Determination of vanadium, nickel,

Goreli, M., Vale, V., Silva, M.M., Damin, I.C.F., Filho, P.J. S., Welz. B., (2008), Determination

Guidr, J.M., Snddon, J., (2002), Fate of vanadium determined by nitrous oxide-acetylene

Hammond, J.L., Lee, Y., Noble, C.O., Beck, J.N., Proffitt, C.E., Sneddon, J., (1998),

Istas – Flores, C.A., Buenrostro-Gonzalez, E., Lira-Galeana, C., (2005), Comparisons between

Jakubowski, N., Feldmann, J. Stuewere, D., (1992), Analytical improvement of pneumatic nebulization in ICP-MS by desolvation, *Spectrochim. Acta*, 47B, 107-118. Kaminski, T.J., Fogler, H.S., Wolf, N., Wattana, P., Mairal, A., (2000), Classification of

Kelly, R.W., Long, S.E., Mann, J.L., (2003), Determination of mercury in SRM crude oils and

Khuhawar, M.Y., Arain, G.M., (2006), Liquid chromatographic determination of vanadium

Khuhawar, M.Y., Lanjwani, S.N., (1996), Simultaneous high performance liquid

thiosemicarbazone as derivatizing reagent, *Talanta*, 68, 535-541.

spectrophotometry with a graphite furnace, *Mirochem. J*. 57, 94-106.

aromatics, resins and asphaltenes ,*Talanta*, 74, 1385-1391.

oils*, Energy Fuels*, 16, 1571-1575.

spectrometry, *Anal. Chem*. 56, 2452-2460.

oil, *Microchem. J*., 73, 363-366.

*Energy Fuels*, 19, 2080-2088.

kinetics, *Energy Fuels*, 14, 25-30.

combustion, *Anal. Bioanal. Chem*., 376, 753-758.

*Talanta*, 47, 261-66.

510-517.

and heavy crude fractions by inductively coupled argon plasma atomic emission spectrometry and flame atomic absorption spectrometry, *Anal. Chem*. 57, 1853-1863.

vanadyl compounds in heavy crude petroleums by liquid chromatography/graphite furnace atomic absorption spectrometry, *Anal. Chem*. 56,

and nickel compounds in heavy crude petroleum and asphaltenes by reverse phase and size-exclusion liquid chromatography/graphite furnace atomic absorption

iron, copper, and lead in petroleum fraction by atomic absorption

of volatile and non-volatile nickel and vanadium compounds in crude oil using electrothermal atomic absorption spectrometry after oil fractionation into saturates,

flame atomic absorption spectrometry in unburned and burned Venezuelen crude

Determination of cadmium, lead and nickel by simultaneous multi element flame atomic absorption spectrometry in burned and unburned Venezuelan crude oils,

open column chromatography and HPLC. SARA fractionations in petroleum,

asphaltenes via fractionation and the effect of heteroatom content on dissolution

refined products by isotope dilution cold vapour ICP-MS using closed system

in petroleum oils and mineral ore samples using 2-acetylpyridine-4-phenyl-3-

chromatographic determination of vanadium, nickel, iron and copper in crude

de Campos, R.C., dos Santos, H.R., Grinberg, P., (2002), Determination of copper, iron, lead

de la Guardia, M., Lizondo, M.J., (1993), Direct determination of nickel in fuel oil by atomic

de Oliveira, A.P., Gomes Neto, J.A., Ferreira, M.M.C., (2006), Use of exploratory data

de Souza, R.M., da Silverira, C.L.P., (2006), Determination of Mo, Zn, Cd, Ti, Ni, V, Fe, Mn,

de, B.M Souza, R.M., Mathias., Searminio, I.S, de Silveira, C.L.P Aucelio, R.Q., (2006),

Dilli, S., Patsalides, E., (1981), Determination of vanadium in petroleum crudes and fuel oils

Dittert, I.M., Silva, J.S.A., Araujo, R.G.O., Curtius, A.J., Welz, B., Becker-Ross, H., (2010),

Duyck, C., Miekeley, N., Porto da Silveria, C.L., Aucelio, R.Q., Campos, R.C., Grinberg, P.,

Duyck, C.; Miekcley, N. Silveira, C.L.P. Szatmari, P., (2002), Trace element determination in

El-Gayar, M., Mostafa, M.S., Abdelfallah, A.E., Barakat, A.O., (2002), Application of

Ellis, J., Rechsteiner, C., Moir, M., Wilbur, S. (2011), Determination of volatile nickel and

*Encyclopedia Britannica*, Available at http://www.britannica.com., Accessed October 16,2011. Evans, C.R., Rogers, M.A., Baily N.J.I., (1971), Evolution and alteration of petroleum in

coupled plasma mass spectrometry., *J. Anal. At. Spectrom*. 9, 939-943. Ekanem, E.J., Lori, J.A., Thomas, S.A., (1998), Ashing procedure for the determination of

metals in petroleum fuels, *Bull. Chem. Soc. Ethiop*. 2, 9-16.

related types , *Fuel Process. Technol*. 79, 13-28.

western Canada ,*Chem. Geol*. 8,147-170.

by gas chromatography, *Anal. Chem. Acta*, 128, 109-119.

spectrometry. *J. Anal. At. Spectrom*. 25, 590-595.

three-component solutions, *Spectrochim. Acta*, Part B 57, 15-28.

absorption spectrometry using emulsion, *At. Spectr*., 6, 208-211.

*Microchem. J*., 82, 137-141.

*Microchim. Acta*, 153, 219-225.

939-951.

26, 1674-1678.

simultaneous metals in fuel ethanol by GFAAS, *Eclet. Quim*.31,7-12.

and nickel in gasoline by electrothermal atomic absorption spectrometry using

analysis in the evaluation of chemical modifier for direct determination and

Cr and Co in crude oil using inductively coupled plasma optical emission spectrometry and sample introduction as detergentless micro-emulsions,

Comparison between two sample emulsification procedures for the determination of Mo, Cr, V and Ti in diesel and fuel oil by ICP OES along with factorial design,

Simultaneous determination of cobalt and vanadium in undiluted crude oil using high resolution continuum source graphite furnace atomic absorption

Brandao, G. P., (2007), The determination of trace elements in crude oil and its heavy fractions by atomic spectrometry, *Spectrochim. Acta, Part B, At. Spectrom*. 62,

crude oil and its fractions by inductively coupled plasma mass spectrometry using ultrasonic nebulization of toluene solutions, *Spectrochim. Acta*, 57B, 1979-1990. Ebdon, E.L., Evans, H., Pretorius, W. G., Rowland, S.J., (1994), Analysis of geoporphyrins by

high-temperature gas chromatography ion chromatography with inductively

geochemical parameters for classification of crude oils from Egypt into source-

vanadium species in crude oil and crude oil fractions by gas chromatography coupled to inductively coupled plasma mass spectrometry, *J. Anal. At. Spectrom*.,

Determination of Metal Ions in Crude Oils 141

Meeravali, N.N., Kumar, S.J., (2001), The utility of a W-Ir permanent chemical modifier for

Mello, P.A., Pereira, J.S.F., Moraes, D.P., Dressler, V.L., Flores, E.M.M., Knapp, G., (2009),

Microwave assisted acid digestion of sediments, sludges, soils and oils, (1994), US-EPA, A

Milner, O.J., Glass, J.R., Kirchner, J.P., Yurick, A.N., (1952), Determination of trace metals in

Mirza, M.A., Kandhro, A.J., Khuhawar, M.Y., Arain, R., (2009), MEKC determination of

Munoz, P.A.A., Correia, P.R.M., Nascimento, A.N., Silva, C.S., Oliveira P.V., Angnes, L.,

Munoz, R.A.A., Correia, P.R.M., Nascimento, A.N., Silva, C.S., Oliveira, P.V., Angnes, L.,

Murillo, M., Chirinos, J., (1994), Use of emulsion systems for the determination of sulphur,

Nakamoto, Y., Ishimaru, T., Endo, N., Matsusaki, K., (2004), Determination of vanadium in

Odermatt, J., Curiale, J., (1991), Organically bound metals and biomarkers in the Monterey formation of the Santa Maria basin, California, *Chem. Geol*. 91, 99-113. Oliveira, E., (2003), Sample preparation for atomic spectroscopy: evolution and future trends

Osibanjo, O., Kakulu, S.E., Ajayi, S.Q., (1984), Analytical application of inorganic salt

Pena, M.E., Manjarrez, A., Campero, A., (1996), Distribution of vanadyl porphyrins in a Mexican offshore heavy crude oil, *Fuel processing Technol*., 46, 171-182. Periria, J.S.F., Moraes, D.P., Antes, F.G., Dieht, L.D., Santos, F.P., Guimaraes, R.C.L.,

crudes by atomic absorption spectrophotometry, *Analyst*, 109, 109-127. Ozcan, M., Akman, S., (2005), Determination of Cu, Co and Pb in gasoline by electrothermal

atomic emission spectrometry*, J. Anal. At. Spectrom*. 9, 237-240.

induced combustion, *J. Anal. At. Spectrom*. 24, 911-916.

techniques. *Energy and Fuel,* 21, 295-302.

techniques, *Energy and Fuel*, 21, 295-302.

tungsten, *Anal. Sci*. 20, 739-741.

,*J. Braz. Chem. Soc.,* 14, 1-17.

assemblies, *Anal. Chim. Acta*, 169, 1-29.

3051, http://www.epa.gov/osw/hazard/testmethods.

crudes and other petroleum oils, *Anal. Chem*., 24, 1728-1732.

532.

3169-3177.

the determination of Ni and V in emulsified fuel oils and naphtha by transverse heated electrothermal atomic absorption spectrometer, *J. Anal. At. Spectrom*. , 6, 527-

Nickel, vanadium and sulphur determination by inductively coupled plasma optical emission spectrometry in crude oil distillation residues after microwave,

vanadium from mineral ore and crude petroleum oil samples using precapillary chelation with bis(salicylaldehyde)tetra-methylethylenediimine, *J. Sep. Sci*., 32,

(2007), Electroanalysis of crude oil and petroleum based fuel for trace metals: Evaluation of different micro-wave assisted sample decompositions and stripping

(2007), Electroanalysis of crude oil and petroleum based fuels for trace metals, Evaluation of different microwave-assisted sample decomposition and stripping

nickel and vanadium in heavy crude oils samples by inductively coupled plasma

heavy oils by atomic absorption spectrometry using graphite furnace coated with

standards and mixed-solvent systems to trace-metal determination in petroleum

atomic absorption spectrometry using aqueous standard addition in gasoline– ethanol–water three-component system , *Spectrochim Acta*, Part B 60, 399-402. Pelizzetti, E., Pramauro, E., (1985), Analytical applications of organized molecular

Fonseca, T.C.O., Dressler, V.L., Flores, E.M.M., (2010), Determination of metals and

petroleum oils using bis(acetylpivalmethane)ethylenediimine as complexing reagent, *Talanta*, 43, 767-770.

Khuhawar, M.Y., Lanjwani, S.N., Khaskhely, G.Q., (1995), High performance liquid

Korn, M.G.A., Andrade, J.B., de Jesus, D.S., Valfrado, A., Lemos, M.L.S.F., Bandeira, W.N.L.,

Kowalewask Z., Ruszezynska, E., (2005), Cu determination in crude oil distillation, products

Kumat, S.J., Gangadharan, S., (1999), Determination of trace elements in naphtha by

Langmyhr, F.J., Adalen, U., (1980), Direct atomic absorption spectrometric determination of

Las Ebdon, E.H.V., Warren, G.R., Stephen, J.R., (1994), Analysis of geoporphyrins by high

Lepri, F.G., Welz, B., Borges, D.L.G., Silva, A.F., Vale, M.G.R., Heitmann, U., (2006),

Lord, C.J., (1991), Determination of trace metals in crude oil by inductively coupled plasma

Luz, M.S., Oliveira, P.V., (2011), Simultaneous determination of Cr, Fe, Ni and V in crude oil

Magyar, B., Lieneman, P., Vonmont, H., (1986), Some effects of aerosol drying and oxygen

Mansfield, C.T., Berman, B.N., Thomas, J.V., Mehrotna, A.K., McCann, J.M., (1995),

Marqueza, N., Ysambertta, F., De La Cruz, C. (1999), Three analytical methods to isolate and

Lubricants : Petroleum and coal, *Anal. Chem.,* 67, 333R-337R.

absorption spectrometry, *Anal. Chim. Acta*, 558, 195-200.

analyte transfer to aqueous solution, *Spectrochim. Acta*, 60B, 351-359. Kumar, U., Dorzey, J.G., Caruzo, J.A., (1994), Metalloporphyrins speciation by liquid

derivatizing reagents, *J. Chromatogr. A.*, 766, 159-164.

techniques: A review, *Talanta*, 69, 16-24.

*Sci*., 32, 282-285.

365-368.

1599.

*At. Spectrom*., 14, 967-971.

*Spectrom*. 9, 939-943.

*Methods*, 3, 1280-1283.

*Acta*, 395, 343-349.

plasma, *Spectrochim. Acta*, 41B, 27-38.

reagent, *Talanta*, 43, 767-770.

petroleum oils using bis(acetylpivalmethane)ethylenediimine as complexing

chromatographic determination of vanadium in crude petroleum oils using bis(salicylaldehyde)tetramethylethylenediimine, *J. Charomatogr. A*, 689, 39-43. Khuhawar, M.Y., Memon, A.A., Bhanger, M.I., (1997), Capillary gas chromatographic

determination of vanadium in crude petroleum oil using fluorinated ketoamines as

dos Santos, M.A., Bezerra, F.A.C., Amorim, A.S., Ferreira, S.L.C., (2006), Separation and preconcentration procedures for the determination of lead using spectrometric

by atomic absorption and inductively coupled plasma mass spectrometry after

chromatography and inductively coupled plasma mass spectrometry, *J. Chromatogr.*

inductively coupled plasma mass spectrometry using water-in-oil emulsion, *J. Anal.*

copper, nickel and vanadium in coal and petroleum coke , *Anal. Chim. Acta*, 115.

temperature inductively coupled plasma mass spectrometry and high performance liquid chromatography inductively coupled plasma mass spectrometry, *J. Anal. At.*

Speciation analysis of volatile and nonvolatile vanadium compounds in Brazilian crude oils using high resolution continuum source graphite furnace atomic

mass spectrometry with micro-emulsion sample introduction, *Anal. Chem*., 63, 1594-

by emulsion sampling graphite furnace atomic absorption spectrometry, *Anal.*

feeding on the analytical performance of an inductively coupled nitrogen-argon

characterize vanadium and nickel porphyrins from heavy crude oils, *Anal. Chim.*

Determination of Metal Ions in Crude Oils 143

Stiger, H.P.M., de Haan, R., Guicherit, C.P.A,. Dekkers, M.L., (2000), Determination of

Tan, S.H., Horlick, H., (1986), Background spectral features in inductively coupled

Tao, H., Murakami, T., Tominaga, M., Miyazaki, A., (1998), Mercury speciation in neutral

Teserovsky, E., Arpadjan, E., (1991), Behaviour of various organic solvents and analytes in electrothermal atomic absorption spectrometry, Anal. Atom. Spectrom. 6, 487-491. Thomaidis, N.S., Piperaki, E.A., (1996), Comparison of chemical modifiers for the

Treibs, A., (1936), Chlorophyll and minerals in organic Häminderivate, *Angew Chemie*, 49,

Trindade, J.M., Marques, A.L., Lopes, G.S., Margues, E.P., Zhang, J., (2006), Arsenic

absorption spectrometry after acid digestion, *Anal. Chim. Acta*, 311, 85-91. Udoh, A.P., Thomas, S.A., Ekanem., (1992), Application of P-xylenesulphonic acid as ashing reagent in the determination of trace metals in crude oils, *Talanta,* 39, 1591-1595. Vale, M.G.R., Damin, I.C.F., Klassen, A., Silva, M.M., Welz, B., Silva, A.F., Lepri, F.G.,

graphite furnace atomic absorption spectrometry, *Microchem. J*., 77, 131-140. Vale, M.G.R., Silva, M.M., Damim, I.C.F., Sanches Filho, P.J., Welz. B., (2008), Determination

Vilhunen, J.K., Bohlen, A., Schmeling, M., Klockenkamper, R., Klockow, D., (1997), Total

Wilhelm, S.M., Bloom, N., (2000), Mercury in petroleum (Review), *Fuel processing Technology*,

Wilhelm, S.M., Liang, L., Kirchgesser, D., (2006), Identification and properties of mercury

Wondimu, W., Goessler, W., Irgolie, K.J., (2000), Microwave digestion of residual fuel oil for

Xu, H., Que, G., Yu, D., Lu, J.R., (2005),Characterization of petroporphyrins using

plasma/mass spectrometry, *Appl. Spectrosc*. 40, 445-460.

atomic absorption spectrometry, *Analyst*. 121, 111-117.

aromatics, resins and asphaltenes, *Talanta*, 74, 1385-1391.

industries, *Spectrochim Acta*, B, 52, 953-959.

species in crude oil, *Energy Fuels* 20, 180-186.

spectrometry, *Energy and Fuel*, 19, 517-524.

spectrometry. *Fresenius J. Anal. Chem*., 367, 35-42.

spectrometry, *J. Anal. At. Spectrom*. 13, 1085-1093.

107, 451-464.

682-686.

63, 1-27.

cadmium, zinc, copper, chromium and arsenic in crude oil cargoos, *Environ. Pollut*.

gas condensate by gas chromatography – inductively coupled plasma mass

determination of vanadium in water and oil samples by electrothermal atomization

determination in gasoline by hydride generation atomic absorption spectroscopy combined with a factorial experimental design approach, *Fuel*, 85, 2155-2161. Turunen, M., Peraniemi, S., Ahlgren, M., Westerholm, H., (1995), Determination of trace

elements in heavy oil samples by graphite furnace and cold vapour atomic

Borges, D.L.G., Heitmann., (2004), Method development for the determination of nickel in petroleum using line-source and high resolution continuum-source

of volatile and non-volatile nickel and vanadium compounds in crude oil using electrothermal atomic absorption spectrometry after oil fraction into saturates,

reflection X-ray fluorescence analyses of samples from oil refining and chemical

the determination of trace elements by inductively coupled plasma mass

ultraviolet-visible spectroscopy and laser desorption ionization time of flight mass

metalloids in light and heavy crude oil by ICP-MS after digestion by microwaveinduced combustion, *Microchem. J*., 96, 4-11.

Peters, K.E., Walters, C.C., Moldowan, J.M., 2nd ed., *The biomarker guide, Volume 2: Biomarkers*

Platteau, O., Carrillo, M., (1995), Determination of metallic elements in crude oil-water

Quadros, D.P.C., Chaves, E.S., Lepri, F.G., Borges, D.L.G., Welz, B., Becker-Ross, H., Curtius,

Quimby, B.D, Dryden, P.C. Sullivan, J.J. (1991), A selective detection of volatile nickel,

Ridyk, B.M., Alturki, Y.I.A., Pillinger, C.T., Eglington, G., (1975), Petroporphyrins as

Rudzinski, W.E., Aminabhavi, T.M., (2000), A review on extraction and identification of

Sant Ana, F.W., Santelli, R.E., Cassella, A.R., Cassella, R.J., (2007), Optimization of an open

Santella, R.E., Bezerra, M.A., Freire, A.S., Oliveira, E.P., de Carvalho, M.F.B., (2008), Non-

Sebor, G., Long, I., Kolihova, D., Wasser, O., (1982) Effect of the type of organometallic iron

Seidl, P.R., Chrisman, E.C.A.N., Carvalin, C.C.V., Leal, K.Z., de Menezes, S.M.C., (2004),

Seidl, P.R., Chrisman, E.C.A.N., Siwa, R.C., de Menezes, S.M.C., Teixeira, M.A.G., (2004),

Sharma, B.K., Sarowha, S.L.S. Bhagat, S.D., Tiwari, R.K., Gupta, S.K., Venkataramani, O.S.,

Silva, M.M., Damin, I.C.F.; Vale, M.G.R., Welz, B., (2007), Feasibility of using solid sampling

Speight, J.G., (2001), *Handbook of Petroleum Analysis*, John Wiley and Sons Inc. New Jersey*,*

prepared as detergent emulsion using GFAAS, *Fuel*, 87, 1617-1622.

by flame atomic absorption spectroscopy, *Analyst*, 107, 1350-1355.

emission spectroscopy, *J. High Res. Chromatogr*., 14, 110-116.

indicators of geothermal maturation ,*Nature* 256, 563-565.

induced combustion, *Microchem. J*., 96, 4-11.

emulsion by flame AAS, *Fuel*, 74, 74-76.

spectrometry, *Energy Fuels*, 24, 5907-5911.

New York, 2004.

14, 464.

359.

519.

*Materials*, 149, 67-74.

*J. Dispersion Sci. Technol*. 25, 349-353.

residues, *Pet. Sci. Technol*., 22, 961-971.

TLC-FID technique, *J. Anal. Chem*., 360, 539-544.

metalloids in light and heavy crude oil by ICP-MS after digestion by microwave-

*and isotopes in the petroleum exploration and earth history*, Cambridge University Press,

A.J., (2010), Evaluation of Brazilian and Venezuelan, Crude oil samples by means of the simultaneous determination of Ni and V as their total and non-volatile fractions using high resolution continuum source graphite furnace atomic absorption

vanadium and iron porphyrins in crude oils by gas chromatography atomic

crude oil and related products using supercritical fluid technology , *Energy Fuels*,

focused microwave oven digestion procedure for determination of metal in diesel oil by inductively coupled plasma optical emission spectrometry, *J. Hazardous*

volatile vanadium determination in petroleum condensate, diesel and gasoline

and copper compounds on the determination of both metals in petroleum samples

NMR analysis of asphaltenes separated from vacuum residues by selected solvents,

Critical variables for the characterization of asphaltenes extracted from vacuum

(1998), Hydrocarbon group type analysis of petroleum heavy fractions using the

graphite furnace atomic absorption spectrometry for speciation analysis of volatile and non-volatile compounds of nickel and vanadium in crude oil. *Talanta*, 71, 349-

**Part 3**

**Crude Oil Biology**

**Part 3**

**Crude Oil Biology**

144 Crude Oil Emulsions – Composition Stability and Characterization

Yan, Z., Hou, X., Jones, B. T., (2003),Determination of wear metals in engine oil by mild acid

Zang, Y.D. Uden, P.C., (1994), High temperature gas chromatography – atomic emission

extraction disks, *Talanta*, 59, 673-680.

222.

digestion and energy dispersive X-ray fluorescence spectrometry using solid phase

detection of m`etalloporphyrins in crude oils , *J. High Resolut. Chromatogr*., 17, 217-

**8**

*Brazil*

**Crude Oil by EPR**

*Paramagnética Eletrônica (LAFLURPE)*

and Eduardo Di Mauro

Marilene Turini Piccinato, Carmen Luisa Barbosa Guedes

*Universidade Estadual de Londrina (UEL) /Laboratório de Fluorescência e Ressonância*

Our goal was based on environment questions. Environmental accidents involving crude and by-product oils have motivated laboratory research to evaluate photodegradation in monitored environments, as well as the characterization of crude and by-product oils. EPR

Electron paramagnetic resonance (EPR) or Electron spin resonance (ESR) is a high resolution spectroscopy that consists in energy absorption of microwave, for electron spin, in the presence of a magnetic field (Ikeya, 1993). As the name itself suggests, EPR is applied in samples containing some paramagnetic species or used as an investigative method, to verify the presence of some paramagnetic species. Paramagnetism is characteristic of species with

Paramagnetism of organic molecules arises almost entirely from unpaired electron spins (Gerson & Huber, 2003). The spin quantum number (�) is the sum of the corresponding numbers, 1/2 of the unpaired electrons. The two possible configurations for an unpaired electron in the presence of an external magnetic field (spin up and spin down) have different energies, which are represented by energy level diagrams (Fig. 1). In the absence of an

Energy showed in different spin states in the presence of an external magnetic field is known as "Zeeman effect" and depends on ���� and the magnetic moment �����) of the

According to the above equation, the energy levels to an unpaired electron have energies

��� = + �

�� = ����� (1)

� ��� (2)

applied magnetic field, the two spin states are of equal energy (Bunce, 1987).

**1. Introduction**

**2. What is EPR?**

equal to

and

was the spectroscopic technique used as analysis tool.

a total magnetic moment different from zero.

electron (Ikeya, 1993). The Zeeman energy is given by

### **Crude Oil by EPR**

Marilene Turini Piccinato, Carmen Luisa Barbosa Guedes and Eduardo Di Mauro *Universidade Estadual de Londrina (UEL) /Laboratório de Fluorescência e Ressonância Paramagnética Eletrônica (LAFLURPE) Brazil*

#### **1. Introduction**

Our goal was based on environment questions. Environmental accidents involving crude and by-product oils have motivated laboratory research to evaluate photodegradation in monitored environments, as well as the characterization of crude and by-product oils. EPR was the spectroscopic technique used as analysis tool.

#### **2. What is EPR?**

Electron paramagnetic resonance (EPR) or Electron spin resonance (ESR) is a high resolution spectroscopy that consists in energy absorption of microwave, for electron spin, in the presence of a magnetic field (Ikeya, 1993). As the name itself suggests, EPR is applied in samples containing some paramagnetic species or used as an investigative method, to verify the presence of some paramagnetic species. Paramagnetism is characteristic of species with a total magnetic moment different from zero.

Paramagnetism of organic molecules arises almost entirely from unpaired electron spins (Gerson & Huber, 2003). The spin quantum number (�) is the sum of the corresponding numbers, 1/2 of the unpaired electrons. The two possible configurations for an unpaired electron in the presence of an external magnetic field (spin up and spin down) have different energies, which are represented by energy level diagrams (Fig. 1). In the absence of an applied magnetic field, the two spin states are of equal energy (Bunce, 1987).

Energy showed in different spin states in the presence of an external magnetic field is known as "Zeeman effect" and depends on ���� and the magnetic moment �����) of the electron (Ikeya, 1993). The Zeeman energy is given by

$$E\_\mathbf{z} = g\beta H\mathbf{M}\_\mathbf{s} \tag{1}$$

According to the above equation, the energy levels to an unpaired electron have energies equal to

$$E\_{\rm z+} = +\frac{1}{2}g\beta H\tag{2}$$

and

$$E\_{z-} = -\frac{1}{2}g\beta H\tag{3}$$

Crude Oil by EPR 149

In addition to the interaction of the unpaired electron with the external magnetic field, interaction can also occur with the nuclei of atoms. If the nucleus of the paramagnetic ion has a magnetic moment, this will interact with the electronic moment, resulting in hyperfine

The interaction of the unpaired electron with the nucleus splits the electron energy levels, generating a structure called spectral hyperfine structure or hf splitting (Poole, 1967). Each "*Ms* state" being split into a closely spaced group of ሺʹܫ ͳሻlevels (Orton, 1968). ܫis the nuclear spin quantum number. The way in which these give rise to hyperfine splitting of the

Fig. 3. Schematic diagram of the hf splitting for unpaired electron interaction with a nucleus

Transitions are allowed under the following selection rules:οܯ ൌ േͳ, for electron spin levels splitting, and ο݉ ൌ Ͳ, for nuclear spins. For the sample taken, the allowed transitions are indicated by arrows in Fig. 3. Each one of these transitions gives rise to a resonance line in the EPR spectrum (Fig. 4). The spacing between the observed lines, usually in gauss, provides the hyperfine coupling constant (*A*). The spacing between lines is always

Fig. 4. Resonance lines for unpaired electron interaction with a nucleus of nuclear spin *I* =

symmetrically disposed about the center of the spectrum.

1/2 and indication for the hyperfine coupling constant (*A*).

structure in the EPR spectrum (Orton, 1968).

resonance lines is illustrated in Fig. 3.

of nuclear spin *I* = 1/2.

corresponding to spin up (�� = + � � ) and spin down (�� = − � � ) respectively.

If an oscillating field of radiation in the microwave range acts on an unpaired electron in the presence of a magnetic field, transitions between two energy states are possible. The transition between energy levels will only occur when the following resonance condition is satisfied:

$$h\nu = g\beta H\tag{4}$$

This happens when the incident radiation is equal to the separation between the Zeeman energy levels. �� is the energy of the absorbed photon, � is a constant for the electron, the Bohr magneton, � is the external magnetic field, and � (g-factor) is a constant characteristic of spin system (approximately 2.0 for organic free radicals) (Janzen, 1969). The g-factor is sensitive to the chemical neighborhood of the unpaired electron.

In EPR spectroscopy it is common to record the spectrum as first derivative curve (Fig. 2a), as opposed to the direct absorption curve (Fig. 2b), which is the conventional presentation in high-resolution NMR (Bunce, 1987).

Fig. 2. **a** EPR spectrum as a first derivative curve; **b** Absorption curve.

) and spin down (�� = − �

��

� ���

� ��� (3)

) respectively.

�� = ��� (4)

�

��� = − �

Fig. 1. Energy levels of a single electron in presence of an external magnetic field.

sensitive to the chemical neighborhood of the unpaired electron.

Fig. 2. **a** EPR spectrum as a first derivative curve; **b** Absorption curve.

high-resolution NMR (Bunce, 1987).

If an oscillating field of radiation in the microwave range acts on an unpaired electron in the presence of a magnetic field, transitions between two energy states are possible. The transition between energy levels will only occur when the following resonance condition is

This happens when the incident radiation is equal to the separation between the Zeeman energy levels. �� is the energy of the absorbed photon, � is a constant for the electron, the Bohr magneton, � is the external magnetic field, and � (g-factor) is a constant characteristic of spin system (approximately 2.0 for organic free radicals) (Janzen, 1969). The g-factor is

In EPR spectroscopy it is common to record the spectrum as first derivative curve (Fig. 2a), as opposed to the direct absorption curve (Fig. 2b), which is the conventional presentation in

�

corresponding to spin up (�� = + �

satisfied:

In addition to the interaction of the unpaired electron with the external magnetic field, interaction can also occur with the nuclei of atoms. If the nucleus of the paramagnetic ion has a magnetic moment, this will interact with the electronic moment, resulting in hyperfine structure in the EPR spectrum (Orton, 1968).

The interaction of the unpaired electron with the nucleus splits the electron energy levels, generating a structure called spectral hyperfine structure or hf splitting (Poole, 1967). Each "*Ms* state" being split into a closely spaced group of ሺʹܫ ͳሻlevels (Orton, 1968). ܫis the nuclear spin quantum number. The way in which these give rise to hyperfine splitting of the resonance lines is illustrated in Fig. 3.

Fig. 3. Schematic diagram of the hf splitting for unpaired electron interaction with a nucleus of nuclear spin *I* = 1/2.

Transitions are allowed under the following selection rules:οܯ ൌ േͳ, for electron spin levels splitting, and ο݉ ൌ Ͳ, for nuclear spins. For the sample taken, the allowed transitions are indicated by arrows in Fig. 3. Each one of these transitions gives rise to a resonance line in the EPR spectrum (Fig. 4). The spacing between the observed lines, usually in gauss, provides the hyperfine coupling constant (*A*). The spacing between lines is always symmetrically disposed about the center of the spectrum.

Fig. 4. Resonance lines for unpaired electron interaction with a nucleus of nuclear spin *I* = 1/2 and indication for the hyperfine coupling constant (*A*).

Crude Oil by EPR 151

Asymmetrical lines of the free radical were observed in all EPR spectra (Figs. 6 and 7). However, asymmetry was more pronounced in the spectra obtained in the W- band (Figs. 6c and 7c). The asymmetry in the line is due to the superposition of all the possible orientations of the paramagnetic species in the system and to the contributions of different chemical

Fig. 7. Free radical EPR spectra of Colombian crude oil at room temperature obtained in: **a**

The values of the line width οܪ in the spectra increased linearly with the microwave frequency utilized in EPR experiments (Fig. 8). The οܪ values are obtained directly from the

Fig. 8. Line width οܪ of the free radical signal versus microwave frequency of EPR spectra recorded in the X-, Q- and W– bands at room temperature. , οܪ) Arabian petroleum); ,

The increase in values of the line width οܪ could be due either, to the superposition of all the possible orientations of the paramagnetic species with anisotropic g-factor in the system and/or to the contribution of different chemical species with a different g-factor to the free radical. If the line is the result of a single chemical species, the first cause would be entirely responsible for the broadening of the line with the variation of the microwave frequency

οܪ) Colombian petroleum); , οܪଵȀଶ (Arabian petroleum); , οܪଵȀଶ (Colombian

species that interact with the unpaired electron.

X- band; **b** Q- band; **c** W- band (Di Mauro et al., 2005).

petroleum).

EPR spectrum, according to the representation shown in Fig. 6c.

In crude and by-product oils, the paramagnetic species presence allows that the RPE technique assists to elucidate the complex chemical composition of these systems. Petroleum and related materials such as heavy oils, asphalt, pitch coal tar, tar sands, kerogen, and oil shale have been studied by EPR (Ikeya, 1993).

#### **3. Crude oil by EPR**

The EPR spectra of crude oils show signals of two different paramagnetic centers, namely, the vanadyl group VO2+ and free radical (Guedes et al., 2001, 2003). These are overlapped in the same magnetic field range (Fig. 5a), being the very intense central line associated with organic free radical (Montanari et al., 1998; Scott & Montanari, 1998; Yen et al, 1962) (Fig. 5b).

The free radical gives rise to a single line corresponding to the transition between the spin +1 2⁄ and −1 2⁄ . This line is interpreted as resulting from the superposition of the signals of the different species of free radicals with very close values of g-factor in crude oil asphaltenes (Guedes et al., 2001, 2003).

Fig. 5. **a** EPR spectrum for Brazilian crude oil; **b** Signal of the free radical; **c** Simulated spectrum for VO2+ (Guedes et al., 2001).

To try to understand the free radical line, Arabian crude oil (Arabian Light Crude Oil) and Colombian crude oil (Cusiana Crude oil) were studied by EPR in X- (9 GHz), Q- (34 GHz), and W- bands (34 GHz). The spectra obtained at different frequencies are shown in Fig. 6 and Fig. 7.

Fig. 6. Free radical EPR spectra of Arabian crude oil at room temperature obtained in: **a** Xband; **b** Q- band; **c** W- band; ��� �⁄ is the half height separation of the EPR derivative peak and ���� is the separation of the EPR derivative peak (Di Mauro et al., 2005).

In crude and by-product oils, the paramagnetic species presence allows that the RPE technique assists to elucidate the complex chemical composition of these systems. Petroleum and related materials such as heavy oils, asphalt, pitch coal tar, tar sands, kerogen, and oil

The EPR spectra of crude oils show signals of two different paramagnetic centers, namely, the vanadyl group VO2+ and free radical (Guedes et al., 2001, 2003). These are overlapped in the same magnetic field range (Fig. 5a), being the very intense central line associated with organic

The free radical gives rise to a single line corresponding to the transition between the spin +1 2⁄ and −1 2⁄ . This line is interpreted as resulting from the superposition of the signals of the different species of free radicals with very close values of g-factor in crude oil

free radical (Montanari et al., 1998; Scott & Montanari, 1998; Yen et al, 1962) (Fig. 5b).

Fig. 5. **a** EPR spectrum for Brazilian crude oil; **b** Signal of the free radical; **c** Simulated

To try to understand the free radical line, Arabian crude oil (Arabian Light Crude Oil) and Colombian crude oil (Cusiana Crude oil) were studied by EPR in X- (9 GHz), Q- (34 GHz), and W- bands (34 GHz). The spectra obtained at different frequencies are shown in Fig. 6

Fig. 6. Free radical EPR spectra of Arabian crude oil at room temperature obtained in: **a** Xband; **b** Q- band; **c** W- band; ��� �⁄ is the half height separation of the EPR derivative peak

and ���� is the separation of the EPR derivative peak (Di Mauro et al., 2005).

shale have been studied by EPR (Ikeya, 1993).

asphaltenes (Guedes et al., 2001, 2003).

spectrum for VO2+ (Guedes et al., 2001).

and Fig. 7.

**3. Crude oil by EPR**

Asymmetrical lines of the free radical were observed in all EPR spectra (Figs. 6 and 7). However, asymmetry was more pronounced in the spectra obtained in the W- band (Figs. 6c and 7c). The asymmetry in the line is due to the superposition of all the possible orientations of the paramagnetic species in the system and to the contributions of different chemical species that interact with the unpaired electron.

Fig. 7. Free radical EPR spectra of Colombian crude oil at room temperature obtained in: **a** X- band; **b** Q- band; **c** W- band (Di Mauro et al., 2005).

The values of the line width οܪ in the spectra increased linearly with the microwave frequency utilized in EPR experiments (Fig. 8). The οܪ values are obtained directly from the EPR spectrum, according to the representation shown in Fig. 6c.

Fig. 8. Line width οܪ of the free radical signal versus microwave frequency of EPR spectra recorded in the X-, Q- and W– bands at room temperature. , οܪ) Arabian petroleum); , οܪ) Colombian petroleum); , οܪଵȀଶ (Arabian petroleum); , οܪଵȀଶ (Colombian petroleum).

The increase in values of the line width οܪ could be due either, to the superposition of all the possible orientations of the paramagnetic species with anisotropic g-factor in the system and/or to the contribution of different chemical species with a different g-factor to the free radical. If the line is the result of a single chemical species, the first cause would be entirely responsible for the broadening of the line with the variation of the microwave frequency

Crude Oil by EPR 153

Fig. 10. Simulated spectra of VO2+ in crude oil and indication of lines corresponding to the

EPR spectra with hyperfine interaction assist in the identification of the porphyrin or nonporphyrin vanadium complexes in crude oil (Saraceno et al., 1961; Espinosa et al., 2001). The experimental parameter used in this identification is ��� (chemical shift), which expresses chemical changes. This is calculated from the spectroscopic factors ������ = (��00�� � ��) × 10�� (Dickson & Petrakis, 1974). The different values obtained experimentally for the ��� parameter represent structural differences in the distribution of the ligands around the VO2+

Since laboratory monitoring has shown photochemical degradation of crude oil, an efficient process for oil oxidation and removal must also occur in the environment (Guedes, 1998). Several scientific investigations have been carried out in an attempt to reduce the actual damages caused by-products that attack nature. In some studies, sunlight and artificial light were used on crude oil in order to verify the changes caused by all sunlight spectrum and some specific wavelengths. Monitoring the paramagnetic species in crude oil by EPR is possible to follow the changes in the molecular structure of the oils, once it reflects changes

Crude oils were irradiated with Hg lamp and He-Ne laser. Two types of oil were used, with three different samples. One sample is from Campos Basin - RJ. The other two were obtained from Arabian oil: part of the oil was used without treatment (total Arabian oil), and part was distilled at 260 °C, (partial Arabian oil). The oil samples were subjected to irradiation under commercial mercury lamp (street lighting), of 450 W, which had its protective cover removed. Oil samples were also subjected to irradiation under He-Ne laser with an output of 15 mW and monochromatic emission of 632 nm. EPR measurements were performed on the BRUKER ESP 300E Series equipment, operating in X- band (9 GHz) at

parallel and perpendicular directions in relation to the applied magnetic field.

in complexes.

**4. Degradation of Crude oil by EPR**

in the unpaired electron neighborhood.

**4.1 Degradation by artificial light**

room temperature.

and we would be able to mathematically simulate the signal, thus acknowledging that it corresponds to a single species. However, a mathematical simulation of the free radical signal for the EPR spectra in three bands (X-, Q-, and W- bands) with a set of parameters corresponding to a single species does not coincide exactly with the experimental signal, signaling that the hyperfine interaction of the unpaired electron with neighborhood correspond to more than one species of radical in the molecular structure of the crude oil asphaltenes (Di Mauro et al., 2005).

The vanadyl compounds (VO2+) produce EPR signals less intense (Fig. 3c), with anisotropic g-factor and hf splitting. For the vanadium in the presence of an external magnetic field, the interaction of electron spin (�=� �⁄ ) with the nucleus V51 (�=� �⁄ ) has 16 possible states distributed between the two values S (�� = + � � and �� = − � � ), as shown in diagram (Fig. 9).

Fig. 9. Schematic diagram of the hf splitting for unpaired electron interaction with a nucleus of nuclear spin *I* = 7/2 and allowed transitions to vanadyl compounds (VO2+).

The expected spectrum, considering the allowed transitions for vanadium (+4) in natural asphaltenes, is composed of sixteen axially anisotropic lines (Fig. 10), being eight lines for the direction parallel, and eight lines for the direction perpendicular to the applied magnetic field. This EPR spectrum from crude oil asplaltenes is similar to the spectrum of etioporphyrin (I) when dissolved in low-viscosity oil (O'Reilly, 1958; Saraceno et al., 1961).

The spectrum of vanadyl can be interpreted in terms of the following spin Hamiltonian with axial symmetry (O'Reilly, 1958):

$$\mathcal{H} = g\_{\parallel} \beta H\_{\mathbf{z}} \mathbb{S}\_{\mathbf{z}} + g\_{\perp} \beta (H\_{\mathbf{x}} \mathbb{S}\_{\mathbf{x}} + H\_{\mathbf{y}} \mathbb{S}\_{\mathbf{y}}) + A\_{\parallel} I\_{\mathbf{z}} \mathbb{S}\_{\mathbf{z}} + A\_{\perp} (I\_{\mathbf{x}} \mathbb{S}\_{\mathbf{x}} + I\_{\mathbf{y}} \mathbb{S}\_{\mathbf{y}}) \tag{5}$$

When the molecule is rotating about with a correlation time much shorter than the reciprocal of the spread of the spectrum in frequency, Eq. (5) is reduced to an ''isotropic'' Hamiltonian, with �� = �� �)�� ⁄ <sup>∥</sup> + ���)(O'Reilly, 1958).