Determination of the Enantiomers of Methionine and Cyst(e)ine in the Form of Methionine-sulphon and Cysteic Acid After Performic Acid Oxidation by Reversed Phase High Performance Liquid Chromatography

In the quantitative analysis of cystine, cysteine and methionine content of foods and feeds, the sulphur containing amino acids are often oxidised by performic acid before hydrolysis of the protein to make the determination more punctual. The applicability of the performic acid oxidation to the quantification of the enantiomers of sulphur-containing amino acids has been examined. An reversed phase high performance liquid chromatography (RPHPLC) method was developed for determination of the amount of cysteic acid and methionine-sulphon enantiomers and the rate of the conversion during oxidation from cystine and cysteine into cysteic acid and from methionine to methionine-sulphon was determined. Racemization of the L-cysteine and Lmethionine was negligible during performic acid oxidation, and therefore the process can be applied before hydrolysis of the protein during quantification of enantiomers of sulphur containing amino acids. The separation between the acidic amino acids (Asp, Glu) and the oxidised from of the sulphur-containing amino acids at the applied gradient system is very good, and the resolution of the peaks were better than 1.4 in every case