Patent ID: 7445909

Claim:
A method for detecting reactive metabolites of a drug candidate comprising (a) incubating a drug candidate with a mixture comprising a non-labeled trapping agent that is γ-glutamyl-cystein-glycin, an isotopically-labeled trapping agent that is γ-glutamyl-cystein-glycin that is labeled at 1 to 17 positions with at least one isotope selected from the group consisting of 13 C, 15 N, 18 O, 2 H, 3 H, 34 S, and a drug metabolizing enzyme; and (b) detecting one or more said reactive metabolites by detecting corresponding isotopic doublets in a neutral loss mass spectrum of a product of step (a), wherein the doublet differs in mass by the difference in mass between the non-labeled trapping agent and the isotopically labeled trapping agent.