Mass Spectrometry: Application to Steroid and Peptide Research*

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Abstract
Introduction THIS SEEMS an opportune time for reviewing the impact of mass spectrometry on endocrine research. Twenty-five years ago Biemann et al. (1) published data on the mass spectrometry of small peptides, and Vandenheuval et al. first described the gas chromatography (GC) of steroids (2). Twenty years ago the first integrated gas chromatography-mass spectrometer system became available. This was made possible by the research of Ryhage who had fabricated and evaluated an interface for connecting the two parts which had the role of selectively removing the majority of the carrier gas (3). With the introduction of gas chromatography-mass spectrometry (GC/MS) it became possible to routinely characterize all components eluting from a GC column. Sjövall (4) published the first data on using this technique for the multicomponent mass spectrometric identification of plasma steroid sulfates. In terms of steroid identification and quantification the years since have been devoted to refining instrumentation and technique. Resolution of steroids improved with the introduction first of glass capillary columns (5); these were later replaced with fused-silica. These latter columns are flexible and now have stationary phase bonded to the surface which leads to robustness and long life. Capillary columns also have low carrier-gas flow rate which allows their direct insertion into the mass spectrometer rendering the interface, whose invention allowed the technique to be developed initially, to be largely made redundant. Great improvements have been made in derivatization techniques necessary for protecting steroids against thermal breakdown (6), and years have been spent improving methods for extracting steroids from aqueous media and separating free steroids from steroid conjugates (7). Naturally, GC/MS instruments have become more reliable and easier to use. In particular, instrument conditions and data processing are now largely managed by computer. The potential for selected-ion-monitoring in quantitative analysis was demonstrated (8). Chemical ionization was introduced (9) which allowed molecular weight and structural information to be obtained on steroids which fragment too readily by electron impact. With all these developments GC/MS has become a very powerful alternative and a technique complimentary to those already used in the endocrine laboratory.

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