Introduction to Mass Spectrometry

Mass spectrometry (MS) is a sensitive and powerful analytical technique, in which ionized sample molecules are separated according to their mass to charge ratios (m/z ) by the application of electric and/or magnetic fields. If the ionization regime deposits sufficient excess energy, a proportion of the sample molecules will dissociate, the pattern of product ions formed being dependent on the structure of the intact compound (Fig. 1 ). A mass spectrum thus consists of the masses (strictly mass to charge ratios, m/z ) of these ions plotted against abundance. Interpretation of the spectrum thus affords information about both the mol wt and the structure of the sample. By the standards of most other physical methods, mass spectrometry is fairly sensitive, requiring somewhere between low picomoles and nanomoles of material, depending on the ionization method employed, but against this must be set its destructive nature. The present introduction aims to provide a brief overview of the technique, to define some of the key terms, and to offer a short tour of some of the different instruments that are more or less legitimately called mass spectrometers. Readers wishing a more detailed account should consult refs. 1 –9 . Arecent volume of Methods in Enzymology (5 ) devoted entirely to mass spectrometry is particularly recommended, since both instrumentation and applications are comprehensively covered.