we propose to modify proteins during the sample preparation for the electrophoretic size separation and alter their functional groups and so suppress the existing charged groups . moreover , these modifications reverse the sign of the charge of the charged groups and thus make a complex formation between proteins and ionic surfactant easier . similarly we disclose modification of glycoproteins when the carbohydrate component is oxidized with periodate . we disclose here a protein denaturing composition for sample preparation of proteins prior their electrophoretic size separation , consisting of : a ) an ionic surfactant , b ) an electrolyte , c ) a reducing reagent cleaving disulfidic bridges , d ) a mobility modifier that reacts with proteins and changes the electrophoretic mobility of the complex between said protein and said ionic surfactant . said ionic surfactant is selected from the group of surfactants consisting of sodium dodecylsulfate , lithium dodecylsulfate , sodium tetradecylsulfate , sodium n - lauroylsarcosinate , hexadecyltrimethylammonium bromide , hexadecyltrimethylammonium chloride , hexadecyldimethylethylammonium bromide , octadecyltrimethylammonium bromide , tetradecyltrimethylammonium bromide , and dodecyltrimethylammonium bromide . said electrolyte is selected from the group of electrolytes consisting of potassium chloride , potassium phosphate , potassium acetate , potassium sulfate , potassium nitrate , potassium cyanate , ammonium chloride , ammonium phosphate , ammonium acetate , ammonium sulfate , ammonium nitrate , sodium chloride , sodium phosphate , sodium acetate , sodium sulfate , sodium nitrate , sodium borate , tris hydrochloride , ethanolamine hydrochloride , diethanolamine hydrochloride , triethanolamine hydrochloride , bis - tris - propane hydrochloride , bis - tris hydrochloride , methylglucamine hydrochloride , ethylenediamine hydrochloride , tetramethylethylenediamine hydrochloride , and aminomethylpropanediol hydrochloride . said reducing reagent cleaving disulfidic bridges is selected from the group of compounds consisting of mercaptoethanol , dithiotreitol , dithioerythriol , tris ( carboxyethyl ) phosphine , thioacetic acid , thiopropionic acid , and cysteamine . said mobility modifier is selected from the group of reagents consisting of i . 1 - ethyl - 3 -( 3 - dimethylaminopropyl ) carbodiimide hydrochloride , ii . acetic anhydride , aconitic anhydride , citraconic anhydride , phtalic anhydride , succinic anhydride , glutaric anhydride , itaconic anhydride , propionic anhydride , iii . salt of periodic acid , particularly sodium periodate , iv . salt of cyanic acid particularly potassium cyanate , salt of sulfocyanic acid , v . dithiodialkylcarboxylic acid particularly dithiodiglycolic acid , dithiodipropionic acid , and dithiodibenzoic acid , also dithiodialkylamine , vi . low - fluorescence isothiocyanate , particularly sulfophenyl isothiocyanate , carboxyphenyl isothiocyanate , disulfophenyl isothiocyanate , trisulfophenyl isothiocyanate , and dicarboxyphenyl isothiocyanate , vii . low - fluorescence succinimidyl ester , viii . low - fluorescence sulfonyl chloride , ix . low - fluorescence dichlorotriazine , x . low - fluorescence tetrafluorophenylester . specifically we disclose a protein denaturing composition consisting of about 0 . 1 m potassium cyanate , about 1 % hexadecyltrimethylammonium chloride , and about 1 % tris ( carboxyethyl ) phosphine and also a protein denaturing composition consisting of about 0 . 1 m sodium periodate , about 1 % hexadecyltrimethylammonium chloride , about 1 % tris ( carboxyethyl ) phosphine , and about 100 mm sodium acetate . we further disclose a protein denaturing composition consisting of about 0 . 1 m sodium thioglycolate , about 1 % hexadecyltrimethylammonium chloride , and about 10 mm tris ( carboxyethyl ) phosphine . we also disclose a protein denaturing composition consisting of about 0 . 1 m potassium cyanate , about 1 % sodium dodecylsulfate , and about 1 % dithiotreitol . we also disclose a protein denaturing composition consisting of about 0 . 1 m sodium periodate , about 1 % sodium dodecylsulfate , about 1 % dithiotreitol , and about 100 mm sodium acetate . further we disclose a method for denaturation and sample preparation of proteins prior to their size separation by electrophoresis , consisting of the steps : mixing the protein sample with an ionic surfactant , electrolyte , reducing reagent cleaving disulfidic bridges , and mobility modifier that reacts with proteins and changes the electrophoretic mobility of the complex between said protein and said ionic surfactant ; said mobility modifier is selected from the group of reagents consisting of 1 - ethyl - 3 -( 3 - dimethylaminopropyl ) carbodiimide hydrochloride , acetic anhydride , aconitic anhydride , citraconic anhydride , phtalic anhydride , succinic anhydride , glutaric anhydride , itaconic anhydride , propionic anhydride , a salt of periodic acid , particularly sodium periodate , a salt of cyanic acid , particularly potassium cyanate , a salt of sulfocyanic acid , dithiodialkylcarboxylic acid , dithiodialkylamine , low - fluorescence isothiocyanate , low - fluorescence succinimidyl ester , low - fluorescence sulfonyl chloride , low - fluorescence dichlorotriazine , low - fluorescence tetrafluorophenylester , and heating the prepared mixture at 40 ° c .- 100 ° c . for 1 - 60 min . we also disclose a method for capillary sieving electrophoresis with cationic surfactant for size separation of proteins , consisting of the steps : a ) preparing a protein sample by reacting the protein with the protein mobility modifier , said mobility modifier selected from the group of reagents consisting of 1 - ethyl - 3 -( 3 - dimethylaminopropyl ) carbodiimide hydrochloride , acetic anhydride , aconitic anhydride , citraconic anhydride , phtalic anhydride , succinic anhydride , glutaric anhydride , itaconic anhydride , propionic anhydride , salt of periodic acid , particularly sodium periodate , salt of cyanic acid , particularly potassium cyanate , salt of sulfocyanic acid , dithiodialkylcarboxylic acid , dithiodialkylamine , low - fluorescence isothiocyanate , low - fluorescence succinimidyl ester , low - fluorescence sulfonyl chloride , low - fluorescence dichlorotriazine , low - fluorescence tetrafluorophenylester , b ) rinsing the separation capillary ; c ) filling the capillary with a separation medium for capillary electrophoretic size separation of proteins , said separation medium consisting essentially of a cationic surfactant ; an acidic buffer ; and a sieving polymer , wherein said sieving polymer is selected from the group consisting of linear polyacrylamide , poly ( dimethyl acrylamide ), poly ( hydroxyethyl acrylamide ), poly ( hydroxypropyl acrylamide ), poly ( ethoxyethyl acrylamide ), poly ( vinyl alcohol ), poly ( vinyl pyrrolidone ), hydroxyethyl cellulose , scleroglucan , guaran , locust bean gum , glucomannan , pullulan , dextran , and poly ( ethylene oxide ), with a proviso that when said sieving polymer is poly ( ethylene oxide ), it is in the concentration from about 16 g / l to about 60 g / l ; d ) sample injection , wherein the capillary inlet is washed by a triple immersion in distilled water , then the capillary inlet and cathode are immersed in the sample , capillary outlet and anode are immersed in a vial containing separation medium , and an injection voltage from about 0 . 5 kv to about 12 kv is applied between the anode and cathode for about 1 s to about 60 s ; e ) separation , wherein the capillary inlet and cathode are immersed in a vial containing said separation medium , capillary outlet and anode are immersed in other vial containing said separation medium , then a separation voltage from about 1 kv to about 20 kv being applied between the anode and cathode for about 1 minute to about 20 minutes ; f ) detection , wherein absorption of monochromatic light having wavelength from about 210 nm to about 420 nm is measured and plotted in electropherogram for further data analysis . the separations described in these examples were performed in 3d ce capillary electrophoresis instrument at 20 ° c . in a bare or coated capillary of internal diameter 75 μm and outer diameter 360 μm with uv detection at 214 nm or 420 nm carbamylation of cytochrome c for an improved accuracy of molecular weights by capillary sieving electrophoresis with cationic surfactant 5 mg bovine heart cytochrome c was dissolved in 820 μl water and mixed with 40 μl of 25 % cetyltrimethylammonium chloride , 40 μl of 10 % tricarboxyethyl phosphine , and 100 μl of 1 m kcno . after dissolving , the mixture was heated at 70 ° c . for 20 min and then cooled to room temperature . oxidation of ovalbumin with naio 4 for an improved accuracy of molecular weights by capillary sieving electrophoresis with cationic surfactant 5 mg of ovalbumin was dissolved in 1 ml of 0 . 1 m sodium acetate buffer , ph 5 . 5 and mixed with 75 μl of 0 . 2 m naio 4 and 50 μl of 25 % cetyltrimethylammonium chloride . the mixture was heated at 40 ° c . for 10 min . then 50 μl of 50 % glycerol was added . carbamylated cytochrome c prepared by the procedure in example 1 was analyzed by capillary electrophoresis in a coated capillary ( u . s . pat . no . 7 , 799 , 195 ) 50 μm id , 360 μm od , total length 335 mm , effective length 250 mm . first the capillary was flushed with distilled water then it was filled with 100 mm β - alanine citrate , ph 3 . 3 . carbamylated cytochrome c was injected electrokinetically at + 5 kv for 10 s and separated at + 10 kv for 30 min . cytochrome c was detected by measuring light adsorption at 214 nm or 420 nm ( fig1 ). analysis of proteins by capillary sieving electrophoresis with a cationic surfactant capillary sieving electrophoresis with a cationic surfactant of proteins was performed in a bare capillary 75 μm id , 360 μm od , total length 335 mm , effective length 250 mm . the capillary was flushed with distilled water and filled with a composition containing 16 g / l polyethylene oxide ( m w , 600 k ), 100 mm β - alanine glutamate , 0 . 2 % cetyltrimethylammonium chloride . proteins were injected electrokinetically at + 8 kv for 15 s , separated at + 10 kv for 20 min , and detected by uv adsorption at 214 nm ( fig2 and 3 ). modified proteins showed changed migration mobility . molecular weight of proteins determined by capillary sieving electrophoresis with a cationic surfactant μ = l t × l eff v × t m ( 1 ) where l t is the total capillary length , l eff is the effective capillary length , v is the applied voltage and t m is the migration time of protein . logarithmic molecular weights of proteins were plotted against the calculated mobilities . using suitable proteins as molecular weight standards , a calibration curve was plotted ( fig4 ) and an equation , which describes the plot , was used to calculate the apparent molecular weights of the tested proteins . cytochrome c with a true molecular weight 12 , 400 exhibited apparent molecular weight of 56 , 200 , i . e ., the error of the molecular weight was about 350 % whereas the carbamylated cytochrome c , having approximately the same true molecular weight , showed the apparent molecular weight of 12 , 100 , which corresponds to a relative error of − 2 . 3 %. ferguson plot for proteins separated by capillary sieving electrophoresis with a cationic surfactant to measure the dependence of protein mobilities on the concentration of the sieving polymer in capillary sieving electrophoresis with a cationic surfactant , the electrophoretic separation was performed in 0 - 16 g / l polyethylene oxide ( m w , 600 k ), 100 mm β - alanine glutamate , 0 . 2 % cetyltrimethylammonium chloride . a bare capillary , 75 μm id , 360 μm od , total length 335 mm , effective length 250 mm , was flushed with distilled water and filled with a composition containing 0 - 16 g / l polyethylene oxide ( m w , 600 k ), 100 mm β - alanine glutamate , 0 . 2 % cetyltrimethylammonium chloride . proteins were injected electrokinetically at + 8 kv for 15 s , separated at + 10 kv for 20 min , and detected by uv adsorption at 214 nm . the protein mobilities μ were calculated from the equation 1 and plotted in the ferguson plot as a function of the sieving polymer concentration ( fig5 ). the ferguson plot showed the anomalous migration of native cytochrome c and the proper migration of carbamylated cytochrome c .