SCREENING STRATEGY FOR THE DETECTION OF DERIVATIZED GLUTATHIONE CONJUGATES BY TANDEM MASS-SPECTROMETRY

A series of glutathione (GSH) conjugates have been analyzed directly by fast atom bombardment tandem mass spectrometry (MS-MS), either In their native forms or following conversion to W-[(benzoyloxy)carbonyl] dimethyl ester derivatives. Upon collision-Induced dissociation (CID), structurally Informative daughter Ions were observed that were diagnostic for the glycine and glutamate residues and characteristic of the chemical nature of the conjugated xenobiotic moiety. For each of the derivatized GSH conjugates examined, the most Intense daughter ion arose by the elimination of glycine methyl ester (-89 u), which contrasted with the elimination of glutamate (-129 u) as the major CID fragmentation of native GSH conjugates. The characteristic change in the fragmentation upon derivatization was exploited to develop a class-specific screening strategy for the detection of GSH conjugates by constant neutral loss scanning for the elimination of glycine methyl ester (-89 u). The analytical utility of this approach was established by identifying three GSH conjugates derived metabollcally from 1,2-dibromo-3-chloropropane and by characterizing a total of six derivatized GSH conjugates derived from xenobiotics of diverse chemical structure. The conversion of GSH conjugates to their N-[(benzoyloxy)-carbonyl] dimethyl ester derivatives conferred excellent chromatographic properties, induced characteristic MS-MS fragmentations, and offered a (53 ± 13 Hold Increase in absolute sensitivitiy when compared with native GSH conjugates. For relatively high-mass (~1000-u) GSH conjugates, a gain In sensitivity could be achieved by the optimization of low-energy collision regimens for neutral loss scanning. © 1990, American Chemical Society. All rights reserved.