Simultaneous Isolation of Nonadjacent m/z Ions Using Mirror Switching in an Electrostatic Linear Ion Trap

Abstract

Simultaneous isolation of ions of disparate mass-to-charge (m/z) ratios is demonstrated via appropriately timed pulsing of entrance and exit ion mirrors in an electrostatic linear ion trap (ELIT) mass spectrometer. Manipulation of the voltages of the entrance and exit mirrors, referred to as “mirror switching”, has been demonstrated as a method in which ions can be both captured and isolated. High resolution isolation (>35 000) was previously demonstrated by selective gating of trapping electrodes to avoid ion lapping while closely spaced ions could continue to separate [Anal. Chem.2019918789]. In this work, we demonstrate that advantage can be taken of the ion lapping phenomenon in an ELIT to enable the simultaneous isolation of ions of disparate m/z ratios using mirror switching. This process is demonstrated with minimal ion loss using isotopologues of three carborane compounds ranging in m/z from 320 to 1020. Simultaneous isolation is demonstrated with the isolation of two and three peaks in separate isotopic distributions as well as with the isolation of alternating isotopologues within the same distribution. Such simultaneous isolation experiments are particularly useful when conducting experiments in which a mass calibrant is needed or when multiplexing in a tandem MS workflow.

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“…The status of the samples to be directly analyzed on-site is highly diversified, ranging from pure compounds to highly complex mixtures with target analytes at trace levels. , While the combination of ambient ionization with DAPI-LIT (linear ion trap) instruments has been proven to be effective, the performance for the direct analysis of complex samples may still be limited to a narrow dynamic concentration or mass-to-charge ( m / z ) range due to the space charge effect associated with ion traps. This needs to be properly handled when analyzing samples with target analytes varying significantly in concentration. − …”

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“…High-resolution ion isolations using mirrorswitching, achieving an isolation resolution of >35 000 (FWHM) for lipid isobars, have been previously demonstrated. 10,11 This makes the ELIT a promising platform for tandem MS, especially for complex mixtures containing isobaric species. Although the isolation and highresolution readout capabilities of the ELIT have been established, dissociation methods are needed to enable the ELIT to be operated as a stand-alone tandem mass spectrometer.…”