resonance light scattering ( rls ) is 
 an elastic scattering and occurs when an incident beam in energy is close to an 
 absorption band .
first established the rls technique to study 
 the biological macromolecules by means of an ordinary fluorescence spectrometer 
 . due to its high sensitivity , selectivity , and convenience ,
rls studies 
 have attracted great interest among researchers . in recent years , rls technique 
 has been used to determine pharmaceutical [ 25 ] , ion 
 , bacteria , and various biological macromolecules , such as nucleic acids [ 810 ] , proteins [ 1115 ] , and peptide 
 . over the years
, numerous analytical methods for cl   in a variety of samples have been developed , such as ion chromatography 
 [ 17 , 18 ] , near - infrared spectrometry , 
 spectroscopy , ion - selective electrode method , turbidimetric 
 method , and so on . among these methods ,
the turbidimetric method was 
 popular and regarded relatively reliable for the quantification of cl .
although it often 
 provided very accurate results , it suffered from the long experimental time , lower 
 sensitivity , and complexity .
partly , because of the lower sensitivity , few 
 of the above methods were applied to determine cl in biological 
 systems .
the classical ion - selective electrode method is currently used in food 
 analysis of cl in drinks . nevertheless , these 
 methods similarly suffered from the drawbacks of low sensitivity and 
 inapplicability to low chloride - containing samples .
the objectives of this report are to establish a rapid , sensitive , and selective rls analytical method 
 to determine of cl and to develop an alternative standard method for determination of cl   in marketing 
 drink .
the obtained results were compared with that of the ion - selective 
 electrode method .
rls spectra were recorded on a jasco fp-6500 spectrofluorophotometer equipped with a thermostated cell 
 compartment using quartz cuvettes ( 1.0 cm ) ( japan ) . the width of excitation and 
 emission slits was set at 3.0 nm .
a bayer rapidchem 744 electrolyte 
 analyzer ( uk ) was used in the ion - selective electrode detection .
the ph measurements were carried out on a 
 phs-3c exact digital ph meter equipped with phonix ag - agcl reference electrode 
 ( cole - parmer instrument co. , ill , usa ) , which was calibrated with standard 
 ph buffer solutions . a stock solution containing 355.00 ng ml of cl
was prepared by 
 dissolving 0.5850 g of nacl ( > 99.99% , sigma co. , mo , usa ) in doubly distilled water and diluting to 
 1000 ml .
the working solutions were obtained by diluting the stock solution 
 prior to use . a working solution of silver nitrate ( 169.87 g ml ) 

all other reagents and solvents were 
 of analytical reagent grade and used as purchased .
hac and nh3h2o ( 0.01 mol l ) 
 were used to control the acidity , while 0.10 mol l nano3 was 
 used to adjust the ionic strength of the aqueous solutions .
an appropriate aliquot of cl working solution was added to 1.0 ml of silver nitrate working 
 solution and diluted to 10.0 ml with water .
after 
 standing for five minutes , the solution was synchronous scanned on the spectroflourometer through the 
 wavelength range of 250750 nm .
the 
 obtained rls spectra were recorded , and the intensity was 
 measured at 571 nm .
the enhanced rls signal of agcl system was represented as i = i  i0 
 ( i and i0 are the rls intensity of the system in the presence and absence of cl , resp . ) . 

the mineral water , pure 
 water , and green tea commonly found in the supermarket were used as samples . 

the famous brands such as nongfu spring , laoshan , nestl , robust , watsons , and 
 masterkong were taken into account .
these samples were diluted with 
 double - distilled water and sterilized by filtration ( 0.2 m ) before testing . 

chloride ion in each sample was determined by the above - mentioned procedures by 
 adding a 1.0 ml aliquot of the prepared sample instead of the chloride ion working solution .
the rls spectra of cl   and agno3 in water were shown in figure 1(a ) and ( b ) , respectively .
it can be seen that 
 the rls intensity of agno3 solution is quite weak in the whole 
 scanning wavelength region .
in contrast , upon addition of trace amount of cl to agno3 solution , a remarkably enhanced rls with a maximum peak at 571 nm was observed 
 under the same conditions ( 1.0 ml of silver nitrate ) .
the 
 addition of increasing cl   to the solution 
 leads to the gradual enhancement in rls intensity , exhibiting a 
 concentration - dependent relationship .
the production of rls and its intensity are correlative with the formation of the aggregate and its 
 particle dimension in solution .
bearing on this point , we 
 inferred that the cl ion may displace 
 no3 ion in agno3 ( aq ) , forming a new agcl ( s ) compound that 
 could be expected to be an aggregate .
the size of agcl ( s ) 
 particles may be much less than the incident wavelength , and thus the enhanced 
 light - scattering signal occurs under the given conditions . in this way , the resonance 
 light scattering formula could be applicable to the agcl 
 system .
the newly - formed agcl ( s ) particles may be 
 ascribed to the higher electrostatic attraction between ag and cl   than that of the 
 coexistent no3 ion .
moreover , the rls is relevant to the 
 size of the formed aggregated species .
hence , the ph value and ionic strength may exert certain influence on the attraction 
 strength and the dimension of suspension particles , and thus the rls production 
 and its intensity .
the rls intensity of agcl and 
 agno3 solution did not change with the variation of ph in range of 
 2.011.0 .
the unexpected observation is that both of the rls intensity of agcl and agno3 system hardly changed with the 
 concentration changes of added nano3 ( figures are not presented ) .
the formation process of 
 aggregation particles generally includes three steps : nucleation , crystal 
 growth , and aggregation .
the size of the particles is one important factor 
 affecting the rls production and its intensity . to improve the reproducibility 
 of rls intensity of a suspension system
however , the agcl 
 system is very stable in 40 minutes and the average deviation of rls signal was 
 found to be lower than 3.80% ( figure is not 
 presented ) .
moreover , the addition order of the reagents has little 
 effect on the rls spectra .
to gain an insight into the rls selectivity of 
 the agcl for detection of cl   in drinks , the 
 interference of some commonly coexistent ions , such as na , zn , 
 ca , fe , mg , al , co3 , 
 so3 , so4 , po4 , 
 k , and i , was investigated under the same conditions .
the results demonstrated 
 that the co3 and po4 in excess of 1000 folds in 
 concentration relative to cl influenced the rls of agcl ( s ) particles . 

this may be due to the formation of extended aggregate around agcl particle cores by the relatively higher 
 negatively - charged ions of co3 and po4 . 

i in the same concentration relative to cl   strongly affected 
 the rls signal . however , chloride is a prominent negatively charged ion of the 
 drinks .
all concentration of other anions is lower than chloride ion . when the 
 concentration of each ion was the same as or somewhat lower than that of cl , no interference 
 was observed ( results were not presented herein ) .
sodium ion ( nano3 ) 
 hardly exerts interference as well as when its concentration reaches to ca .
therefore , the 
 tolerance levels of the interference of these coexisting ions in the samples 
 were very high and the assays can be performed without removing them .
the detection and quantification limits were calculated as sb + 3s and sb + 10s , 
 respectively , where sb is the average rls signal of ten blank solutions ( 16.99 g ml of silver nitrate ) and s is the 
 standard deviation . when the rls intensity at 571 nm was selected , the 
 detection and quantification limit were calculated to be 0.71 ng ml and 1.42 ng ml , respectively , 
 indicating high sensitivity of this method for the determination of cl .
the sensitivity of the rls method is 
 prominently higher than that of turbidimetry 
 ( results are not presented ) .
according to the above standard procedure , the calibration curve was obtained by plotting 
 the concentration of cl against the 
 intensity of rls spectrum at 571 nm under the optimum conditions ( figure 2 ) . 

the linear regression equation using the least square method was i = 26.97 + 27.25ccl ( ng ml)(r = 0.9989 ) in the range of 1.428.52 ng ml of cl .
the proposed 
 method was applied to determine the concentration of cl in drinks and 
 the results were shown in table 2 . to further examine the accuracy of the proposed rls method ,
the recovery experiments were carried out 
 by adding known amounts of cl to drinks 
 diluted samples ( table 3 ) .
the 
 recovery results were obtained in the range of 94.08105.63% , 
 which indicated that the proposed rls method is practical to assay the cl in drinks .
the proposed method was applied to determine the concentration of chloride ion in 
 drinks and the results were shown in table 2 . to verify the veracity and 
 practicality ,
the samples were analyzed simultaneously by the currently used 
 ise method ( table 2 ) .
it can be seen that the results determined by the rls 
 method were almost in agreement with those by the ise method .
the average rsd 
 of the rls method is 1.01%2.43% , which is some lower than that of ise method ( 1.23%3.46% ) , which 
 proved that the rls assay in drinks was practical .
these two methods , rls 
 and ise , can give the similar results of chloride ion in drinks ( table 2 ) . 
 however , the operations of rls and ise methods were significantly different .
as we know , ise 
 method is an electrochemistry analytical method , in which the variation of 
 temperature , fluctuation of voltage , and treatment of electrode may bring on 
 significant influence on the determination though it features high selectivity . 

 a resonance light scattering ( rls ) technique to determine chloride ions in drinks was developed . 
 chloride ions were found to bind ag+ forming agcl aggregates that produced intense resonance scattering light . 
 effects of factors such as acidity , ionic strength , and coexistent interferents on the rls of agcl aggregates were investigated . 
 the ph of solution almost did not affect the production of rls and few foreign species interfered with the detection of chloride ions . 
 the resonance scattering light intensity at the maximum peak of 571 nm was linear to the concentration of chloride ions in the range of 1.428.52 ng ml1 with a detection limit of 0.71 ng ml1 . to determine the feasibility of the proposed method 
 , some samples of water and drinks were analyzed . 
 the attained results were in agreement with that of ion - selective electrode method . 
 good recovery results were also obtained with the range of 94.08105.63% . 
 the sensitivity and selectivity of the rls method are high enough to determine trace amounts of chloride ions without any significant interference from high concentration of other components such as common anions and cations . 
1. INTRODUCTION
2. EXPERIMENTAL
3. RESULTS AND DISCUSSION
4. ANALYTICAL APPLICATIONS