A gas chromatographic-mass spectrometric method for the simultaneous determ
ination of methionine and total homocysteine in human plasma is described.
DL-[H-2(4)]Methionine and DL-[H-2(8)]homocystine were used as internal stan
dards. The method involved reduction of the disulfide bond with dithiothrei
tol, purification by cation-exchange chromatography using a BondElut SCX ca
rtridge and derivatization with isobutyl chlorocarbonate in water-ethanol-p
yridine. Quantitation was performed by selected-ion monitoring of the quasi
-molecular ions of N(O,S)-isobutyloxycarbonyl ethyl ester (IBC-OEt) derivat
ives for methionine and [H-2(4)]methionine, respectively, and the fragment
ions ([M+H-COOisoBu-COOEt](+)) for IBC-OEt derivatives for homocysteine and
[H-2(4)]homocysteine. respectively. The sensitivity, specificity. accuracy
and precision of the method were demonstrated to be satisfactory for measu
ring concentrations of methionine and total homocysteine in human plasma. (
C) 2001 Elsevier Science B.V. All rights reserved.