New SRM Data Dependent Exclusion (MS)n Measurement for Structural Determination of Drug Metabolites Using LC/ESI/Ion Trap MS

New SRM (selected reaction monitoring) data dependent exclusion (MS)n measurement makes it possible to obtain MS3 fragmentation data for all MS2 fragments, useful for structural determination of drug metabolites using ESI ion trap. MS2 fragments are produced by cleavage of all protonated molecules at the lone electron pairs of heteroatoms or the π electrons of double and triple bonds, benzene rings and hetero­rings of drugs. Usually, data dependent MS 3 measurement cleaves only MS2 fragment of highest intensity, that normally does not contain important metabolic sites. Fragmentation data from all parts of drug metabolites is required to determine structure. In addition to the usual basic measurement of protonated molecules and (MS)n fragmentation of drug metabolites, we demonstrate the use of SRM data dependent (MS)n measurement, plus new SRM data dependent exclusion (MS)n measurement for structural determination of metabolites.