Multiply pulsed collision gas for ion axialization in Fourier-transform ion cyclotron resonance mass spectrometry.

We present a new multiply pulsed collision-gas technique for ion axialization for Fourier-transform ion cyclotron resonance (FTICR) high-resolution mass analysis. Ions are axialized in the source trap of a dual-trap FTICR spectrometer by azimuthal quadrupolar irradiation for several tens of seconds at a steady-state pressure maintained by repeated pulses of collision gas (argon), followed by removal of the collision gas and detection at a much lower pressure after transfer to the analyzer trap. Magnitude-mode FTICR mass resolving power, m/delta m approximately 1,770,000, for [M+K]+ ions from laser-desorbed/ionized leucine enkephalin at m/z 594 is demonstrated. This mass resolving power is the highest yet reported for a peptide with any type of laser desorption/ionization mass analyzer.