We present a simple and label-free approach to characterize glutathione (GSH)-trapped reactive metabolites from a single LC-MS analysis employing a linear ion trap mass spectrometer. The GSH specific fragment anion m/z 272 was first generated from the nonselective in-source fragmentation of intact conjugates. GSH conjugates were then detected by selected reaction monitoring (SRM) of the anion pair m/z 272 → 179 or 210. The resultant SRM peaks represented putative GSH conjugates which were then further characterized from their MS and MS(2) data acquired in both positive and negative ion modes. The method is demonstrated with test compounds that are all known to form GSH conjugates.