Desorption Ionization and Fourier Transform Mass Spectrometry for the Analysis of Large Biomolecules

Abstract

The recent developments in biomolecule mass spectrometry can be traced to progress made in new ionization methods and instruments having extended mass range. Early in the development of Fourier transform mass spectrometry (FTMS) Comisarow and Marshall [1] Gross and Wilkins [2] and McIver [3] noted the applicability of this method for the analysis of large molecules. The principle limitation to developing these capabilities was in adapting the available desorption ionization methods to FTMS. High-mass FTMS requires the use of super-conducting magnets, the design of which imposes mechanical limitations in designing such systems, and ultra-high vacuum (less than 10⁻⁸ torr) which is not compatible with many desorption ionization sources and methods, e.g., gaseous discharge primary ion sources and liquid matrices. The first successful demonstration of desorption ionization with FTMS was the laser desorption ionization by Gross [4]. Subsequent to this work our laboratory reported on the use of Cs⁺ ion SIMS with FTMS detection of high-mass ions, e.g., greater than m/z 2000 [5]. These preliminary results demonstrated the feasibility for performing desorption ionization with FTMS,and more recent work from these two laboratories clearly establishes the analytical utility of the method. Also, Wilkins [6] has reported impressive results for laser desorptionFTMS of a variety of biomolecules, and McIver and Hunt [7,8] have obtained excellent data on biomolecules with tandem quadrupole-FTMS system and fast-atom bombardment (FAB) ionization.