Pulsed Gas Introduction for Increasing Peptide CID Efficiency in a MALDI/Quadrupole Ion Trap Mass Spectrometer

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A pulsed valve was used for studying the effects of introducing heavy gases at different stages of operation of a quadrupole ion trap and for increasing the efficiency of collision-induced dissociation (CID) of peptide ions at low values of the Mathieu parametere qz. When amounts of heavy gases comparable to that of the helium buffer gas were introduced during the ion trapping, ion isolation, and mass spectral recording stages, the effects on performance were generally small or negative. However, injection of heavy gases during CID provided considerable improvement in fragmentation efficiency that depended upon the particular gas used, its mass and pressure, and the amplitude of the excitation voltage. Efficient peptide fragmentation could be demonstrated for values of qz as low as 0.05, which permitted trapping of low-mass product ions and (in many cases) full recovery of the amino acid sequence. In this report, examples are provided of monoisotopic tandem mass spectra of peptide ions with masses up to 1570 Da.