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Harper CC, Williams ER. Enhanced Multiplexing in Fourier Transform Charge Detection Mass Spectrometry by Decoupling Ion Frequency from Mass to Charge Ratio. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:2637-2645. [PMID: 31720975 DOI: 10.1007/s13361-019-02330-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 08/27/2019] [Accepted: 08/28/2019] [Indexed: 06/10/2023]
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.
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Affiliation(s)
- Conner C Harper
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA
| | - Evan R Williams
- Department of Chemistry, University of California, Berkeley, CA, 94720-1460, USA.
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Kafader JO, Beu SC, Early BP, Melani RD, Durbin KR, Zabrouskov V, Makarov AA, Maze JT, Shinholt DL, Yip PF, Kelleher NL, Compton PD, Senko MW. STORI Plots Enable Accurate Tracking of Individual Ion Signals. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:2200-2203. [PMID: 31512223 PMCID: PMC6852666 DOI: 10.1007/s13361-019-02309-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Revised: 07/30/2019] [Accepted: 08/02/2019] [Indexed: 05/08/2023]
Abstract
Charge detection mass spectrometry (CDMS) of low-level signals is currently limited to the analysis of individual ions that generate a persistent signal during the entire observation period. Ions that disintegrate during the observation period produce reduced frequency domain signal amplitudes, which lead to an underestimation of the ion charge state, and thus the ion mass. The charge assignment can only be corrected through an accurate determination of the time of ion disintegration. The traditional mechanisms for temporal signal analysis have severe limitations for temporal resolution, spectral resolution, and signal-to-noise ratios. Selective Temporal Overview of Resonant Ions (STORI) plots provide a new framework to accurately analyze low-level time domain signals of individual ions. STORI plots allow for complete correction of intermittent signals, the differentiation of single and multiple ions at the same frequency, and the association of signals that spontaneously change frequency.
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Affiliation(s)
- Jared O Kafader
- Departments of Chemistry and Molecular Biosciences, the Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, IL, 60208, USA
| | | | - Bryan P Early
- Departments of Chemistry and Molecular Biosciences, the Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, IL, 60208, USA
| | - Rafael D Melani
- Departments of Chemistry and Molecular Biosciences, the Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, IL, 60208, USA
| | - Kenneth R Durbin
- Departments of Chemistry and Molecular Biosciences, the Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, IL, 60208, USA
| | | | | | | | | | - Ping F Yip
- Thermo Fisher Scientific, San Jose, CA, 95134, USA
| | - Neil L Kelleher
- Departments of Chemistry and Molecular Biosciences, the Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, IL, 60208, USA
| | - Philip D Compton
- Departments of Chemistry and Molecular Biosciences, the Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, IL, 60208, USA
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Harper CC, Elliott AG, Oltrogge LM, Savage DF, Williams ER. Multiplexed Charge Detection Mass Spectrometry for High-Throughput Single Ion Analysis of Large Molecules. Anal Chem 2019; 91:7458-7465. [PMID: 31082222 DOI: 10.1021/acs.analchem.9b01669] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Applications of charge detection mass spectrometry (CDMS) for measuring the masses of large molecules, macromolecular complexes, and synthetic polymers that are too large or heterogeneous for conventional mass spectrometry measurements are made possible by weighing individual ions in order to avoid interferences between ions. Here, a new multiplexing method that makes it possible to measure the masses of many ions simultaneously in CDMS is demonstrated. Ions with a broad range of kinetic energies are trapped. The energy of each ion is obtained from the ratio of the intensity of the fundamental to the second harmonic frequencies of the periodic trapping motion making it possible to measure both the m/ z and charge of each ion. Because ions with the exact same m/ z but with different energies appear at different frequencies, the probability of ion-ion interference is significantly reduced. We show that the measured mass of a protein complex consisting of 16 protomers, RuBisCO (517 kDa), is not affected by the number of trapped ions with up to 21 ions trapped simultaneously in these experiments. Ion-ion interactions do not affect the ion trapping lifetime up to 1 s, and there is no influence of the number of ions on the measured charge-state distribution of bovine serum albumin (66.5 kDa), indicating that ion-ion interactions do not adversely affect any of these measurements. Over an order of magnitude gain in measurement speed over single ion analysis is demonstrated, and significant additional gains are expected with this multi-ion measurement method.
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