The enantiomer as internal standard for the quantitation of the alkylated amino acid S-methyl-L-cysteine in haemoglobin by gas chromatography-chemical ionisation mass spectrometry with single ion detection.

A method has been developed using gas chromatography-chemical ionisation mass spectrometry for the determination of S-methyl-L-cysteine in rat and human haemoglobin. The D-enantiomer of S-methylcysteine is added as an internal standard prior to the protein hydrolysis and a partial purification of the protein hydrolysate made by ion-exchange column chromatography. The enantiomers of S-methyl-cysteine are separated as their N-trifluoroacetyl n-butyl ester derivatives on a capillary column coated with the chiral stationary phase Chirasil-Val. The use of single ion detection in the assay is three times more sensitive than the use of multiple ion detection with a deuterium labelled internal standard. The method has been applied to haemoglobin samples from rats and humans exposed to methylating agents.