Enhanced Multiplexing in Fourier Transform Charge Detection Mass Spectrometry by Decoupling Ion Frequency from Mass to C
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J. Am. Soc. Mass Spectrom. (2019) DOI: 10.1007/s13361-019-02330-3
RESEARCH ARTICLE
Enhanced Multiplexing in Fourier Transform Charge Detection Mass Spectrometry by Decoupling Ion Frequency from Mass to Charge Ratio Conner C. Harper, Evan R. Williams Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA
Abstract. Weighing single ions with charge detection mass spectrometry (CDMS) makes it possible to obtain the masses of molecules of essentially unlimited size even in highly heterogeneous samples, but producing a mass histogram that is representative of all of the components in a mixture requires substantial measurement time. Multiple ions can be trapped to reduce analysis time but ion signals can overlap. To determine the maximum gains in analysis speed possible with current instrumentation with multiple ion trapping, simulations calculating the frequency and overlap rate of ions with different mass, charge, and energy ranges were performed. For an analyte with a broad mass distribution, such as long chain polyethylene glycol (PEG, 8 MDa), gains in analysis speed of up to 160 times that of prior CDMS experiments are possible. For signals from homogeneous samples, ions with the same m/z have frequencies that overlap and interfere, reducing the effectiveness of multiplexing in experiments where ions have the same energy per charge. We show that by maximizing the decoupling of ion m/z from frequency using a broad range of ion energies, the rate of signal overlap is significantly reduced making it possible to trap more ions. Under optimum decoupling conditions, a measurement speed nearly 50 times greater than that of prior CDMS experiments is possible for RuBisCO (517 kDa). The reduction in overlap due to decoupling also results in more accurate quantitation in samples that contain multiple analytes with different concentrations. Keywords: CDMS, Charge detection mass spectrometry, Multiplexing, Fourier transform, Megadalton, Ion energy, Ion frequency, High-throughput, Decoupling, Native MS Received: 3 June 2019/Revised: 27 August 2019/Accepted: 28 August 2019
Introduction
N
ative mass spectrometry, in which ions of biomolecular molecules and associated macromolecular complexes are produced by electrospray ionization from aqueous solutions containing 100+ mM concentrations of salts [1, 2], is widely used to obtain structural information about molecular ions formed from environments in which they have native structures and reactivities [3]. Information about the stoichiometries and
Electronic supplementary material The online version of this article (https:// doi.org/10.1007/s13361-019-02330-3) contains supplementary material, which is available to authorized users. Correspondence to: Evan Williams; e-mail: [email protected]
structures of complexes can be obtained from tandem mass spectrometry experiments in which mass-selected precursor ions are activated, either through collisions with gaseous molecules or with surfaces, and the resulting fragment ions, typically consisting of intact mo
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