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Mathew A, Giskes F, Lekkas A, Greisch JF, Eijkel GB, Anthony IGM, Fort K, Heck AJR, Papanastasiou D, Makarov AA, Ellis SR, Heeren RMA. An Orbitrap/Time-of-Flight Mass Spectrometer for Photofragment Ion Imaging and High-Resolution Mass Analysis of Native Macromolecular Assemblies. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023. [PMID: 37319176 DOI: 10.1021/jasms.3c00053] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
We discuss the design, development, and evaluation of an Orbitrap/time-of-flight (TOF) mass spectrometry (MS)-based instrument with integrated UV photodissociation (UVPD) and time/mass-to-charge ratio (m/z)-resolved imaging for the comprehensive study of the higher-order molecular structure of macromolecular assemblies (MMAs). A bespoke TOF analyzer has been coupled to the higher-energy collisional dissociation cell of an ultrahigh mass range hybrid quadrupole-Orbitrap MS. A 193 nm excimer laser was employed to photofragment MMA ions. A combination of microchannel plates (MCPs)-Timepix (TPX) quad and MCPs-phosphor screen-TPX3CAM assemblies have been used as axial and orthogonal imaging detectors, respectively. The instrument can operate in four different modes, where the UVPD-generated fragment ions from the native MMA ions can be measured with high-mass resolution or imaged in a mass-resolved manner to reveal the relative positions of the UVPD fragments postdissociation. This information is intended to be utilized for retrieving higher-order molecular structural details that include the conformation, subunit stoichiometry, and molecular interactions as well as to understand the dissociation dynamics of the MMAs in the gas phase.
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Affiliation(s)
- Anjusha Mathew
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Frans Giskes
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Alexandros Lekkas
- Fasmatech Science and Technology, Demokritos NCSR, 15310 Agia Paraskevi, Athens, Greece
| | - Jean-François Greisch
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Centre for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
- Netherlands Proteomics Center, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Gert B Eijkel
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Ian G M Anthony
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Kyle Fort
- Thermo Fisher Scientific (Bremen) GmbH, 28199 Bremen, Germany
| | - Albert J R Heck
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Centre for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
- Netherlands Proteomics Center, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | | | - Alexander A Makarov
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Centre for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
- Thermo Fisher Scientific (Bremen) GmbH, 28199 Bremen, Germany
| | - Shane R Ellis
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Ron M A Heeren
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
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Du S, Jia H, Xu W, Zhai Y. Field-Gradient-Focusing Ion Guide for Enhanced Transfer Efficiency of Low-Mass Ions. Anal Chem 2023; 95:2079-2086. [PMID: 36632644 DOI: 10.1021/acs.analchem.2c05014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Efficient transmission of low-mass ions in a rough vacuum pressure region has always been a challenging issue in mass spectrometry (MS). In this study, a novel ion guide, namely, field-gradient-focusing ion guide (FGF-IG), was proposed to improve the transfer efficiency of ions, especially low-mass ions in a rough vacuum region. The FGF-IG has 12 electrodes whose surfaces gradually narrowed and tilted inward, and its electric field gradually varies from dodecapole (or multipole) to quadrupole along the ion transfer route. The field radius was gradually decreased from 6 to 2 mm in the multipole region (65 mm in length) and finally remained unchanged as 2 mm in the quadrupole region (20 mm in length). By integrating into a miniature mass spectrometer (mini-MS) with a continuous atmospheric pressure interface, this ion guide was optimized in terms of inlet capillary position, radio frequency amplitude, and direct current voltage applied on it. Results showed that a reduced low-mass discrimination effect and improved efficiency of simultaneously transferring mid and low m/z ions were achieved for FGF-IG compared with a conventional ion funnel. Under optimized conditions, a limit of detection of 1 ng/mL was obtained for both reserpine (m/z 609) and arginine (m/z 175) ions by integrating FGF-IG into the mini-MS. The sensitivity of smaller arginine ions using FGF-IG was enhanced by ∼10 times than that obtained using the conventional ion funnel (10 ng/mL) in comparative experiments. The idea of smooth transfer from dodecapole to quadrupole fields could be extended to other multipole fields, as well as in lab-scale MS instruments.
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Affiliation(s)
- Shiyu Du
- School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Heyuan Jia
- School of Life Science, Beijing Institute of Technology, Beijing 100081, China
| | - Wei Xu
- School of Life Science, Beijing Institute of Technology, Beijing 100081, China
- Institute of Engineering Medicine, Beijing Institute of Technology, Beijing 100081, China
| | - Yanbing Zhai
- Institute of Engineering Medicine, Beijing Institute of Technology, Beijing 100081, China
- School of Medical Technology, Beijing Institute of Technology, Beijing 100081, China
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Mathew A, Keelor JD, Eijkel GB, Anthony IGM, Long J, Prangsma J, Heeren RMA, Ellis SR. Time-Resolved Imaging of High Mass Proteins and Metastable Fragments Using Matrix-Assisted Laser Desorption/Ionization, Axial Time-of-Flight Mass Spectrometry, and TPX3CAM. Anal Chem 2022; 95:1470-1479. [PMID: 36574608 PMCID: PMC9850352 DOI: 10.1021/acs.analchem.2c04480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The Timepix (TPX) is a position- and time-sensitive pixelated charge detector that can be coupled with time-of-flight mass spectrometry (TOF MS) in combination with microchannel plates (MCPs) for the spatially and temporally resolved detection of biomolecules. Earlier generation TPX detectors used in previous studies were limited by a moderate time resolution (at best 10 ns) and single-stop detection for each pixel that hampered the detection of ions with high mass-to-charge (m/z) values at high pixel occupancies. In this study, we have coupled an MCP-phosphor screen-TPX3CAM detection assembly that contains a silicon-coated TPX3 chip to a matrix-assisted laser desorption/ionization (MALDI)-axial TOF MS. A time resolution of 1.5625 ns, per-pixel multihit functionality, simultaneous measurement of TOF and time-over-threshold (TOT) values, and kHz readout rates of the TPX3 extended the m/z detection range of the TPX detector family. The detection of singly charged intact Immunoglobulin M ions of m/z value approaching 1 × 106 Da has been demonstrated. We also discuss the utilization of additional information on impact coordinates and TOT provided by the TPX3 compared to conventional MS detectors for the enhancement of the quality of the mass spectrum in terms of signal-to-noise (S/N) ratio. We show how the reduced dead time and event-based readout in TPX3 compared to the TPX improves the sensitivity of high m/z detection in both low and high mass measurements (m/z range: 757-970,000 Da). We further exploit the imaging capabilities of the TPX3 detector for the spatial and temporal separation of neutral fragments generated by metastable decay at different locations along the field-free flight region by simultaneous application of deflection and retarding fields.
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Affiliation(s)
- Anjusha Mathew
- Maastricht
MultiModal Molecular Imaging (M4i) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Joel D. Keelor
- Amsterdam
Scientific Instruments (ASI), Science Park 106, 1098 XG Amsterdam, The Netherlands
| | - Gert B. Eijkel
- Maastricht
MultiModal Molecular Imaging (M4i) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Ian G. M. Anthony
- Maastricht
MultiModal Molecular Imaging (M4i) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Jingming Long
- Amsterdam
Scientific Instruments (ASI), Science Park 106, 1098 XG Amsterdam, The Netherlands
| | - Jord Prangsma
- Amsterdam
Scientific Instruments (ASI), Science Park 106, 1098 XG Amsterdam, The Netherlands
| | - Ron M. A. Heeren
- Maastricht
MultiModal Molecular Imaging (M4i) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands,
| | - Shane R. Ellis
- Maastricht
MultiModal Molecular Imaging (M4i) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands,Molecular
Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, NSW 2522, Wollongong, Australia,
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Mathew A, Eijkel GB, Anthony IGM, Ellis SR, Heeren RMA. Characterization of microchannel plate detector response for the detection of native multiply charged high mass single ions in orthogonal-time-of-flight mass spectrometry using a Timepix detector. JOURNAL OF MASS SPECTROMETRY : JMS 2022; 57:e4820. [PMID: 35347816 PMCID: PMC9287041 DOI: 10.1002/jms.4820] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Revised: 02/25/2022] [Accepted: 03/02/2022] [Indexed: 06/14/2023]
Abstract
Time-of-flight (TOF) systems are one of the most widely used mass analyzers in native mass spectrometry (nMS) for the analysis of non-covalent multiply charged bio-macromolecular assemblies (MMAs). Typically, microchannel plates (MCPs) are employed for high mass native ion detection in TOF MS. MCPs are well known for their reduced detection efficiency when impinged by large slow moving ions. Here, a position- and time-sensitive Timepix (TPX) detector has been added to the back of a dual MCP stack to study the key factors that affect MCP performance for MMA ions generated by nMS. The footprint size of the secondary electron cloud generated by the MCP on the TPX for each individual ion event is analyzed as a measure of MCP performance at each mass-to-charge (m/z) value and resulted in a Poisson distribution. This allowed us to investigate the dependency of ion mass, ion charge, ion velocity, acceleration voltage, and MCP bias voltage on MCP response in the high mass low velocity regime. The study of measurement ranges; ion mass = 195 to 802,000 Da, ion velocity = 8.4 to 67.4 km/s, and ion charge = 1+ to 72+, extended the previously examined mass range and characterized MCP performance for multiply charged species. We derived a MCP performance equation based on two independent ion properties, ion mass and charge, from these results, which enables rapid MCP tuning for single MMA ion detection.
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Affiliation(s)
- Anjusha Mathew
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS)Maastricht UniversityMaastrichtThe Netherlands
| | - Gert B. Eijkel
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS)Maastricht UniversityMaastrichtThe Netherlands
| | - Ian G. M. Anthony
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS)Maastricht UniversityMaastrichtThe Netherlands
| | - Shane R. Ellis
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS)Maastricht UniversityMaastrichtThe Netherlands
- Molecular Horizons and School of Chemistry and Molecular BioscienceUniversity of WollongongWollongongNSWAustralia
| | - Ron M. A. Heeren
- Maastricht MultiModal Molecular Imaging (M4i) Institute, Division of Imaging Mass Spectrometry (IMS)Maastricht UniversityMaastrichtThe Netherlands
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Mathew A, Buijs R, Eijkel GB, Giskes F, Dyachenko A, van der Horst J, Byelov D, Spaanderman DJ, Heck AJR, Porta Siegel T, Ellis SR, Heeren RMA. Ion Imaging of Native Protein Complexes Using Orthogonal Time-of-Flight Mass Spectrometry and a Timepix Detector. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:569-580. [PMID: 33439014 PMCID: PMC7863068 DOI: 10.1021/jasms.0c00412] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 12/22/2020] [Accepted: 12/23/2020] [Indexed: 06/12/2023]
Abstract
Native mass spectrometry (native MS) has emerged as a powerful technique to study the structure and stoichiometry of large protein complexes. Traditionally, native MS has been performed on modified time-of-flight (TOF) systems combined with detectors that do not provide information on the arrival coordinates of each ion at the detector. In this study, we describe the implementation of a Timepix (TPX) pixelated detector on a modified orthogonal TOF (O-TOF) mass spectrometer for the analysis and imaging of native protein complexes. In this unique experimental setup, we have used the impact positions of the ions at the detector to visualize the effects of various ion optical parameters on the flight path of ions. We also demonstrate the ability to unambiguously detect and image individual ion events, providing the first report of single-ion imaging of protein complexes in native MS. Furthermore, the simultaneous space- and time-sensitive nature of the TPX detector was critical in the identification of the origin of an unexpected TOF signal. A signal that could easily be mistaken as a fragment of the protein complex was explicitly identified as a secondary electron signal arising from ion-surface collisions inside the TOF housing. This work significantly extends the mass range previously detected with the TPX and exemplifies the value of simultaneous space- and time-resolved detection in the study of ion optical processes and ion trajectories in TOF mass spectrometers.
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Affiliation(s)
- Anjusha Mathew
- Maastricht
MultiModal Molecular Imaging (M4I) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Ronald Buijs
- NWO
Institute AMOLF Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Gert B. Eijkel
- Maastricht
MultiModal Molecular Imaging (M4I) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Frans Giskes
- Maastricht
MultiModal Molecular Imaging (M4I) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Andrey Dyachenko
- Biomolecular
Mass Spectrometry and Proteomics, Bijvoet Centre for Biomolecular
Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584
CH Utrecht, The Netherlands
- Netherlands
Proteomics Center, Padualaan
8, 3584 CH Utrecht, The Netherlands
| | | | - Dimitry Byelov
- Amsterdam
Scientific Instruments (ASI), Science Park 106, 1098 XG Amsterdam, The Netherlands
| | | | - Albert J. R. Heck
- Biomolecular
Mass Spectrometry and Proteomics, Bijvoet Centre for Biomolecular
Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584
CH Utrecht, The Netherlands
- Netherlands
Proteomics Center, Padualaan
8, 3584 CH Utrecht, The Netherlands
| | - Tiffany Porta Siegel
- Maastricht
MultiModal Molecular Imaging (M4I) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
| | - Shane R. Ellis
- Maastricht
MultiModal Molecular Imaging (M4I) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
- Molecular
Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Ron M. A. Heeren
- Maastricht
MultiModal Molecular Imaging (M4I) Institute, Division of Imaging
Mass Spectrometry (IMS), Maastricht University, 6229 ER Maastricht, The Netherlands
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Hommersom B, Syed SUAH, Eijkel GB, Kilgour DPA, Goodlett DR, Heeren RMA. An ambient detection system for visualization of charged particles generated with ionization methods at atmospheric pressure. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:352-358. [PMID: 26754127 DOI: 10.1002/rcm.7442] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 10/24/2015] [Accepted: 10/26/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE With the current state-of-the-art detection of ions only taking place under vacuum conditions, active pixel detectors that operate under ambient conditions are of particular interest. These detectors are ideally suited to study and characterize the charge distributions generated by ambient ionization sources. METHODS The direct imaging capabilities of the active pixel detector are used to investigate the spatial distributions of charged droplets generated by three ionization sources, named electrospray ionization (ESI), paper spray ionization (PSI) and surface acoustic wave nebulization (SAWN). The ionization spray (ESI/PSI) and ionization plume (SAWN) originating from each source are directly imaged. The effect of source parameters such as spray voltage for ESI and PSI, and the angle of the paper spray tip on the charge distributions, is investigated. Two types of SAWN liquid interface, progressive wave (PW) and standing wave (SW), are studied. RESULTS Direct charge detection under ambient conditions is demonstrated using an active pixel detector. Direct charge distributions are obtained of weak, homogeneous/focused and dispersed spray plumes by applying low, intermediate and high spray potentials, respectively, for ESI. Spray plume footprints obtained for various angles of PSI shows the possibility to focus the ion beam as a function of the paper angle. Differences between two designs of the SAWN interface are determined. Droplet charge flux changes are illustrated in a way similar to a total ion chromatogram. CONCLUSIONS The use of this active pixel detector allows the rapid characterization and optimization of different ambient ionization sources without the actual use of a mass spectrometer. Valuable illustrations are obtained of changes in spatial distribution and number of charges detected for ESI, PSI and SAWN ion plumes. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Bob Hommersom
- FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
- M4I, The Maastricht MultiModal Molecular Imaging Institute, University of Maastricht, Universiteitssingel 50, 6229, ER, Maastricht, The Netherlands
| | - Sarfaraz U A H Syed
- FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
- Amsterdam Scientific Instruments B.V., Science Park 105, 1098 XG, Amsterdam, The Netherlands
| | - Gert B Eijkel
- FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
- M4I, The Maastricht MultiModal Molecular Imaging Institute, University of Maastricht, Universiteitssingel 50, 6229, ER, Maastricht, The Netherlands
| | - David P A Kilgour
- University of Maryland School of Pharmacy, 20 N Pine Street, Baltimore, Maryland, 21201, USA
| | - David R Goodlett
- University of Maryland School of Pharmacy, 20 N Pine Street, Baltimore, Maryland, 21201, USA
- Deurion LLC, 3518 Fremont Avenue #503, Seatle, WA, 98103, USA
| | - Ron M A Heeren
- FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
- M4I, The Maastricht MultiModal Molecular Imaging Institute, University of Maastricht, Universiteitssingel 50, 6229, ER, Maastricht, The Netherlands
- Amsterdam Scientific Instruments B.V., Science Park 105, 1098 XG, Amsterdam, The Netherlands
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Syed SUAH, Maher S, Eijkel GB, Ellis SR, Jjunju F, Taylor S, Heeren RMA. Direct Ion Imaging Approach for Investigation of Ion Dynamics in Multipole Ion Guides. Anal Chem 2015; 87:3714-20. [DOI: 10.1021/ac5041764] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Sarfaraz U. A. H. Syed
- FOM Institute
AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
- TI-COAST, Science Park
904, 1098 XH Amsterdam, The Netherlands
| | - Simon Maher
- Department
of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, United Kingdom
| | - Gert B. Eijkel
- FOM Institute
AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Shane R. Ellis
- FOM Institute
AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
- M4I,
The Maastricht MultiModal Molecular Imaging Institute, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
| | - Fred Jjunju
- Department
of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, United Kingdom
| | - Stephen Taylor
- Department
of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, United Kingdom
| | - Ron M. A. Heeren
- FOM Institute
AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
- TI-COAST, Science Park
904, 1098 XH Amsterdam, The Netherlands
- M4I,
The Maastricht MultiModal Molecular Imaging Institute, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
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A micropixelated ion-imaging detector for mass resolution enhancement of a QMS instrument. Anal Bioanal Chem 2014; 407:2055-62. [DOI: 10.1007/s00216-014-8158-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Revised: 08/29/2014] [Accepted: 09/02/2014] [Indexed: 10/24/2022]
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