A Miniaturized Fourier Transform Electrostatic Linear Ion Trap Mass Spectrometer: Mass Range and Resolution

Abstract

Mass resolution (M/ΔM_FWHM) was increased by reducing the axial length of a Fourier transform electrostatic linear ion trap (FT-ELIT) mass spectrometer. The increase in mass resolution corresponds directly to increased axial ion frequencies in the FT-ELIT. Increased mass resolution was demonstrated for equivalent transient lengths in a 5.25″ versus 2.625″ ELIT using the isotopes of [bradykinin+2H]²⁺ and [insulin+5H]⁵⁺ as test ions. Both bradykinin and insulin show mass resolution increases of ~ 90% allowing baseline resolution of the [insulin+5H]⁵⁺ isotopes after only 300 ms of data acquisition. Relative changes in mass/charge range were explored using mirror switching to trap ions injected axially into the ELIT. When trapping ions using mirror switching, the mass/charge range in a FT-ELIT mass spectrometer for a given switch time is determined by the time required for fast ions to enter and exit the trap after one reflection versus the time it takes for slow ions to enter the trap. By reducing the length of the FT-ELIT mass spectrometer while maintaining a constant distance from the point from which ions are initially accelerated to the entrance mirror, only the low m/z limit is affected for a given mirror switching time. For the two ELIT lengths examined here, the effective mass/charge range at any given switch time is reduced from m/z_low-8.9*m/z_low for the 5.25″ ELIT to m/z_low-5.2*m/z_low for the 2.625″ ELIT. Graphical Abstract.

Keywords: Electrostatic linear ion trap; Fourier transform mass spectrometry; Miniaturization.