Mass spectrometry, a powerful tool for lipid research

Abstract

This review is concerned with developments in the use of mass spectrometry as an analytical tool in the field of lipid structural research. Particular attention is given to instrumental techniques which yield the greatest amount of structural information. Methods are emphasized which increase the diagnostic scope of electron impact (EI) mass spectrometry and provide mechanistic information about fragmentations. Accurate determination of ionic mass is the first step towards a precise description of the various processes by which a molecule fragments. Other esecially useful methods for structural elucidation and mechanistic studies involve labelling with stable isotopes and the analysis of metastable transitions. The importance of the quasi-equilibrium theory (QET) in obtaining a semi-quantitative understanding of cleavage and rearrangement reactions is discussed at some length in relation to the ionization process and the appearance of metastable transitions. Pyrolytic reactions are often troublesome during the mass spectroscopic analysis of polar molecules; a number of criteria are suggested that are suitable for distinguishing pyrolytic and electron impact-induced processes. Advances in the mass spectrometry of polar complex lipids are described, with a caution concerning artefacts which have become more significant with increased instrumental sensitivity, and indicate the need for chemical as well as mass spectrometric characterization of novel compounds.