Abstract
A gas chromatographic–mass spectrometric method for the simultaneous determination of methionine and total homocysteine in human plasma is described. dl-[ 2H 4]Methionine and dl-[ 2H 8]homocystine were used as internal standards. The method involved reduction of the disulfide bond with dithiothreitol, purification by cation-exchange chromatography using a BondElut SCX cartridge and derivatization with isobutyl chlorocarbonate in water–ethanol–pyridine. Quantitation was performed by selected-ion monitoring of the quasi-molecular ions of N( O, S)-isobutyloxycarbonyl ethyl ester (IBC-OEt) derivatives for methionine and [ 2H 4]methionine, respectively, and the fragment ions ([M+H–COOisoBu–COOEt] +) for IBC-OEt derivatives for homocysteine and [ 2H 4]homocysteine, respectively. The sensitivity, specificity, accuracy and precision of the method were demonstrated to be satisfactory for measuring concentrations of methionine and total homocysteine in human plasma.
Published Version
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