Extending the mass-to-charge scannable range of a linear ion trap mass spectrometer through quadrupolar direct current scan

Mass scan methods utilizing quadrupolar direct current (DC) scan were described and performed with a linear ion trap (LIT) through a home-built MS apparatus designed for ion/ion reactions. Both quadrupolar DC downscan and upscan are applicable to the LIT due to the shape of the related Mathieu stability diagram. Besides, a supplementary AC signal could be added to the DC scan process for resonant ejection, which largely enhances the signal-to-noise (S/N) ratios of the spectra. Compared with conventional resonance ejection RF scans, the scannable mass-to-charge (m/z) range in quadrupolar DC scan is much wider. Several protein cations were chosen as test molecules with a m/z scannable range larger than 140,000 Th. Besides, compared with three-dimensional (3D) quadrupolar ion traps (QIT), the LIT is a more suitable mass analyzer for ions with large m/z ratios due to large ion capacity and deep pseudo potential well depths for ions inside the trap. In general, DC scan with LIT offers a new way of rapid detection of ions with extra wide m/z scannable ranges, which has potential applications in research fields such as "top-down" proteomics and native mass spectrometry in the future. (C) 2021 Elsevier B.V. All rights reserved.