METHOD OF HIGH MASS RESOLUTION SCANNING OF AN ION TRAP MASS SPECTROMETER

摘要

A method of using a quadrupole ion trap mass spectrometer for high resolutionmass spectroscopy is disclosed. High resolution of a mass spectrum of adesiredspecies is achieved by first using a slow scanning rate and by first riddingthe trap ofunwanted ions. Accurate mass calibration is achieved by using a referencecompoundof known mass and using a second supplemental AC dipole voltage to eject thereference ions at nearly the same time as the sample ions of interest areejected fromthe trap. This eliminates the need to scan the trap between the masses of thesampleand reference ions. Space charge in the trap is held constant, therebyeliminating amajor source of mass axis instability, by using the results of one scan tocontrol theionization time during the next scan. Preferably, during ionization abroadbandsupplemental dipole voltage is applied to the ion trap to rid it of unwantedions.During a portion of the ionization time the broadband signal is constructed toretainonly sample ions in the ion trap, and during the remainder of the ionizationtime thebroadband signal is constructed to retain both sample and reference ions inthe ion trap.By adjusting the relative lengths of the two portions of the ionization timethe totalspace charge in the ion trap can be held constant notwithstanding variationsin sampleion concentration.