ABSTRACT

I. INTRODUCTION Time-of-flight (TOF) mass spectrometers, coupled to matrix-assisted laser desorption ion sources (MALDI), have in the last few years been used mainly for the determination of molecular weights [1,2]. Hereby, many aspects of biomolecular analysis have been revolutionized, expecially speed, accuracy, and sensitivity of molecular weight determinations. Previously, the different mass spectrometric techniques have been most useful for relat­ ing fragmentations, occurring in the mass spectrometer, to molecular struc­ ture. Because a significant portion of molecules are fragmented by laser light, investigations by Kaufmann [3,4] have shown that post-source decay (PSD) processes can be detected in a reflectron instrument. The TOF in­ strument must be equipped with a reflector, preferably of the gridless dou­ ble-stage design. With this instrument configuration, structure-related frag­ ment ions can be measured. The first experiments have demonstrated the usefulness of PSD for sequencing peptides, one of the main application areas [5,6]. PSD spectra have also been published on linear and branched glycans [7,8] and on TV-linked glycopeptides [9].