SEQUENCE-SPECIFIC FRAGMENTATION GENERATED BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION IN A QUADRUPOLE ION-TRAP REFLECTRON TIME-OF-FLIGHTDEVICE

Sequence-specific fragmentation for structural analysis has been gener ated by activation of ions via matrix-assisted laser desorption/ioniza tion (MALDI) in an ion trap storage/reflectron time-of flight device ( IT/reTOF). The key to this work is that ion decay can be induced by MA LDI activation but requires an extended period of time to occur in lar ge peptides. This extended decay period, which may be in excess of 20 ms, is provided in these experiments using the long storage times of t he ion trap device. The ions are stored until decay is complete and th en rapidly pulsed into a reflectron TOF for analysis. Since the ions d ecay within the trap, they ultimately appear as stable ions in the reT OF rather than as metastable decay peaks. The ion fragmentation was fo und to depend strongly on laser power and the rf voltage placed on the ring electrode of the trap. The fragmentation obtained was shown to b e similar to but different from that observed in FAB-low-energy CAD. I n particular, enhanced fragmentation was obtained in the lower mass ra nge and large species could be more easily fragmented than with FAB-lo w-energy CAD. The types of fragmentation for several target peptides a re discussed.