SELECTIVE INJECTION AND ISOLATION OF IONS IN QUADRUPOLE ION-TRAP MASS-SPECTROMETRY USING NOTCHED WAVE-FORMS CREATED USING THE INVERSE FOURIER-TRANSFORM

Broad-band excitation of ions is accomplished in the quadrupole ion tr ap mass spectrometer using notched waveforms created by the SWIFT (sto red waveform inverse Fourier transform) technique. A series of notched SWIFT pulses are applied during the period of ion injection from an e xternal Cs+ source to resonantly eject all ions whose resonance freque ncies fall within the frequency range of the pulse while injecting onl y those analyte ions whose resonance frequencies fall within the limit s of the notch. This allows selective injection and accumulation of th e ions of interest and continuous ejection of the unwanted ions. This is shown to result in significant improvement in S/N ratio, resolution , and sensitivity for the analyte ions of interest. Selective ion inje ction is demonstrated by injecting the protonated molecules of peptide s VSV and gramicidin S and the intact cation of 1-carnitine hydrochlor ide, using singly notched SWIFT pulses. Multiply notched SWIFT pulses are used to simultaneously inject ions of different m/z values of 1-ca rnitine hydrochloride into the ion trap. A new coarse/fine ion isolati on procedure, which employs a doubly notched SWIFT pulse, is demonstra ted for isolating ions of a single m/z value of 4-bromobiphenyl from a population of trapped ions. In this procedure, coarse isolation of a group of adjacent ions is achieved in the first step and is followed b y a fine isolation of ions of a single m/z value from the coarsely iso lated group.