RPHPLC determination of L- and D-cystine and cysteine as cysteic acid

In the quantitative analysis of cystine and cysteine, before hydrolysis the compounds are often oxidized to cysteic acid with performic acid. The appl icability of this process to the quantification of the enantiomers of cysti ne and cysteine has been examined. An RPHPLC: analytical method was develop ed for determination of the amount of cysteic acid enantiomers and the rate of conversion during oxidation from cystine and cysteine into cysteic acid was determined. Racemization of L-cysteine was not significant during oxid ation with performic acid and the process can, therefore, be applied before hydrolysis during quantification of enantiomers of these compounds.