Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry with pulsed in-source collision gas and in-source ion accumulation

A new matrix-assisted laser desorption/ionization (MALDI) source for Fourie r transform ion cyclotron resonance mass spectrometry (FTMS) has been devel oped. The new source is equipped with a hexapole ion guide. The sample on t he laser target is one millimeter from the hexapole ion guide, so that ions are desorbed directly into the guide. A device for pulsing collision gas i n direct proximity to the laser target makes it possible to cool the ions, which have a kinetic energy spread of several electron volts when produced by the MALDI process. These ions are trapped in the hexapole where positive potentials at the laser target and at an extraction plate help trap ions a long the longitudinal axis. After a pre-defined trapping time the voltage o f the extraction plate is reversed and the trapped ions are extracted for t ransmission to the ion cyclotron resonance cell. Accumulation of ions from multiple laser shots in the hexapole before mass spectrometric analysis inc reases sensitivity. Preliminary sensitivity studies with substance P show t hat 10 attomoles of analyte applied on the target can be detected with a si gnal-to-noise (S/N) ratio >15, Copyright (C) 2000 John Wiley & Sons, Ltd.