SELECTIVE INJECTION OF LASER-DESORBED IONS INTO A QUADRUPOLE ION-TRAP WITH 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 into an ion-trap mass spectrometer (ITMS). The FNF waveform is applied to 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 single-pulse laser desorption, the FNF rapidly ejects desorbed matrix ions without reducing the number of target ions that are trapped. When the FNF is used in conjunction with multipole laser-desorption events, accumulation of target m/z ions results in a 40-fold increase in sensitivity over single-shot laser desorption. In addition, the application of sequential filtered noise fields for multiple stages of mass spectral interrogation is demonstrated.