Determination of 16 Amino Acids in Cosmetics by High Performance Liquid Chromatography with Pre-Column Derivatization
A method for the determination of 16 amino acids including glycine,leucine,histidine,valine,methionine,proline,cysteine,threonine,glutamic acid,lysine,tyrosine,arginine,isoleucine,tryptophan,phenylalanine,and alanine in cosmetics by high performance liquid chromatography with 2,4-dinitrofluorobenzene(DNFB)pre-column derivatization was proposed.5 g of cosmetic sample was taken into a 50 mL-centrifuge tube,and 5 mL of water was added.The mixture was sonicated for 10 min and boiled for 15 min.After cooling,15 mL of 35 g·L-1 sulfosalicylic acid solution was added and the mixture was centrifuged at a rotational speed of 10 500 r·min-1 for 20 min.All of the supernatant was taken and its volume was made up to 25 mL with 35 g·L-1 sulfosalicylic acid solution.1 mL of sample solution was taken,and 1 mL of 0.5 mol·L-1 sodium bicarbonate solution(pH 9.0)and 1 mL of 1%(volume fraction)DNFB derivative solution were added.The mixture was heated at 60℃for 10 min and cooled.Its volume was made up to 5 mL with 0.01 mol·L-1 potassium dihydrogen phosphate solution(pH 7.0).16 amino acids in the obtained solution were separated on a X Bridge C18 chromatographic column,and gradient elution was performed using a mobile phase consisting of 0.05 mol·L-1 sodium acetate buffer solution(pH 6.5)containing 1%(volume fraction)DMF and a mixture of acetonitrile-water at a volume ratio of 1∶1 at different volume ratios.The detection was performed at 360 nm.As shown by the results,the linear ranges of the standard curves of 16 amino acids were 0.004-40.0 mg·L-1,with detection limits(3S/N)in the range of 0.1-0.2 mg·kg-1.Test for recovery was made on blank sample by standard addition method at 3 concentration levels,giving results in the range of 89.0%-105%,with RSDs(n=7)of the determined values not more than 10%.This method was applied to the analysis of 11 commercially available cosmetics,and it was shown that the detected amino acid components were mostly histidine,glycine,methionine,and glutamic acid.
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