SELECTIVE INJECTION OF LASER-DESORBED IONS INTO A QUADRUPOLE ION-TRAPWITH A FILTERED NOISE FIELD

We demonstrate the advantages of utilizing a broad-band filtered noise field (FNF) for preferential mass injection of laser desorbed ions in to an ion-trap mass spectrometer (ITMS). The FNF waveform is applied t o the endcap electrodes of the ITMS during the laser-desorption period , and its amplitude and frequency spectrum are adjusted to resonantly eject all ions except those with selected mass-to-charge ratios. In si ngle-pulse laser desorption, the FNF rapidly ejects desorbed matrix io ns without reducing the number of target ions that are trapped. When t he FNF is used in conjunction with multipole laser-desorption events, accumulation of target m/z ions results in a 40-fold increase in sensi tivity over single-shot laser desorption. In addition, the application of sequential filtered noise fields for multiple stages of mass spect ral interrogation is demonstrated.