High-performance tandem mass spectrometry in metabolism studies

1. High-performance tandem mass spectrometry provides unit resolution in both selection of precursor ions and analysis of fragment ions, and extensive and reproducible fragmentation through collisional activation at high energy. 2. Metabolites can be analysed that occur as minor components in h.p.l.c. peaks or other mixtures. Homogeneous isotopic species can be selected for unambiguous analysis of distributions of isotope labels. Fragmentation may be significantly enhanced to provide structural information. Overall, the signal to noise ratio is greatly improved and the spectrum is simplified. 3. These points are illustrated by isotope-labelling studies of the mechanisms of glutathione conjugation of the anti-tumour agent cyclophosphamide, the cytotoxic agent phosphoramide mustard and dimethylbilirubin, an analogue of bilirubin designed to be distinguishable from endogenous bilirubin. Analysis of isomeric mixed disulphides formed between glutathione and a peptide with an internal disulphide bond is discussed. 4. Reaction-induced decomposition is presented as an alternative to collisionally induced decomposition with more efficient energy transfer.