<title>Peptide sequencing using MALDI on time-of-flight and ion trap mass spectrometers</title>

Abstract

Two instruments have been developed in our laboratory for the direct amino-acid sequencing of peptides. The first is a time-of-flight (TOF) mass spectrometer that utilizes a coaxial, curved-field reflectron which provides simultaneous focusing of product ins formed by post- source decay (PSD) and obviates the need for scanning or stepping the reflectron voltage. The second is a matrix-assisted laser desorption/ionization (MALDI) ion trap mass spectrometer (ITMS). In this instrument, MALDI ions are trapped efficiently by ramping the trapping rf field, and a linear mass scale is achieved by modulating the axial excitation voltage during mass scanning. Monoisotopic mass selection and excitation is accomplished using phase- modulated SWIFT (stored waveform inverse Fourier transform) techniques, while efficient CID (collision-induced dissociation) performance is achieved using pulsed introduction of Xe and other heavier gases. Both mass spectrometers have been designed as compact instruments for sequencing peptides in partially fractionated mixtures.