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Pieterse CL, de Kock MB, Robertson WD, Eggers HC, Miller RJD. Rapid deconvolution of low-resolution time-of-flight data using Bayesian inference. J Chem Phys 2019; 151:244307. [DOI: 10.1063/1.5129343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Cornelius L. Pieterse
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Michiel B. de Kock
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
- Department of Physics, Stellenbosch University, Matieland 7602, South Africa
| | - Wesley D. Robertson
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Hans C. Eggers
- Department of Physics, Stellenbosch University, Matieland 7602, South Africa
- National Institute for Theoretical Physics, Matieland 7602, South Africa
| | - R. J. Dwayne Miller
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
- Departments of Chemistry and Physics, University of Toronto, 80 St. George Street, Ontario, Toronto M5S 3H6, Canada
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2
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Ahmed A, Islam S, Solihat NN, Acter T, Kim S. Systematic Investigation into the Differences in the (+) APPI Efficiencies of Positional (Ortho, Meta, and Para) Isomers. B KOREAN CHEM SOC 2019. [DOI: 10.1002/bkcs.11869] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Arif Ahmed
- Department of ChemistryKyungpook National University Daegu 41566 Republic of Korea
| | - Syful Islam
- Department of ChemistryKyungpook National University Daegu 41566 Republic of Korea
| | - Nissa Nurfajrin Solihat
- Department of ChemistryKyungpook National University Daegu 41566 Republic of Korea
- Research Center for BiomaterialsIndonesian Institute of Sciences (LIPI) Cibinong 16911 Indonesia
| | - Thamina Acter
- Department of Mathematical and Physical SciencesEast West University Dhaka 1212 Bangladesh
| | - Sunghwan Kim
- Department of ChemistryKyungpook National University Daegu 41566 Republic of Korea
- Green‐Nano Materials Research Center Daegu 41566 Republic of Korea
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Robinson KN, Steven RT, Race AM, Bunch J. The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:1284-1293. [PMID: 30949969 DOI: 10.1007/s13361-019-02193-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 02/12/2019] [Accepted: 03/11/2019] [Indexed: 06/09/2023]
Abstract
Ultraviolet matrix-assisted laser desorption/ionization mass spectrometry imaging (UV-MALDI MSI) is a widely used technique for imaging molecular distributions within biological systems. While much work exists concerning desorption in UV-MALDI MS, the effects of commonly varied parameters for imaging applications (repetition rate, use of continuous raster mode and raster speed), which determine spatial resolution and limits of detection for the technique, remain largely unknown. We use multiple surface characterization modalities to obtain quantitative measurements of material desorption and analyte ion yield in thin film model systems of two matrix compounds, arising from different UV-MALDI MSI sampling conditions. Observed changes in resulting ablation feature point to matrix-dependent spatial resolution and laser-induced matrix modification effects. Analyte ion yields of 10-9 to 10-6 are observed. Complex changes in ion yield, between spot and raster sampling and arising from varied laser repetition rate and raster speed, are observed. Graphical Abstract.
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Affiliation(s)
- Kenneth N Robinson
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK
- Advanced Materials and Healthcare Technologies Division (AMHT), University of Nottingham, Nottingham, UK
| | - Rory T Steven
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK.
| | - Alan M Race
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK
| | - Josephine Bunch
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK.
- Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, UK.
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Lee S, Ahmed A, Kim S. Solvent composition dependent signal reduction of molecular ions generated from aromatic compounds in (+) atmospheric pressure photoionization mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2018; 32:973-980. [PMID: 29600539 DOI: 10.1002/rcm.8127] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 03/14/2018] [Accepted: 03/16/2018] [Indexed: 06/08/2023]
Abstract
RATIONALE The ionization process is essential for successful mass spectrometric (MS) analysis because of its influence on selectivity and sensitivity. In particular, certain solvents reduce the ionization of the analyte, thereby reducing the overall sensitivity in atmospheric pressure photoionization (APPI). Since the sensitivity varies greatly depending on the solvents, a fundamental understanding of the mechanism is required. METHODS Standard solutions were analyzed using a (+)-APPI Q Exactive ion trap mass spectrometer (Thermo Scientific). Each solution was infused directly into the APPI source at a flow rate of 100 μL/min and the APPI source temperature was 300°C. Other operating mass spectrometric parameters were maintained under the same conditions. Quantum mechanical calculations were carried out using the Gaussian 09 suite program. RESULTS Density functional theory was used to calculate the reaction enthalpies (∆H) of the reactions between toluene and other solvents. The experimental and theoretical results showed good agreement. The abundances of analyte ions were well correlated with the calculated ∆H values. Therefore, the results strongly support the suggested signal reduction mechanism. In addition, linear correlations between the abundance of toluene and analyte molecular ions were observed, which also supports the suggested mechanism. CONCLUSIONS A solvent composition dependent signal reduction mechanism was suggested and evaluated for the (+)-APPI-MS analysis of polyaromatic hydrocarbons (PAHs) generating mainly molecular ions. Overall, the evidence provided in this work suggests that reactions between solvent cluster(s) and toluene molecular ions are responsible for the observed reductions in signal.
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Affiliation(s)
- Seulgidaun Lee
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
| | - Arif Ahmed
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
| | - Sunghwan Kim
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
- Department of Chemistry, Green Nano Center, Daegu, 702-701, Republic of Korea
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Greco V, Piras C, Pieroni L, Urbani A. Direct Assessment of Plasma/Serum Sample Quality for Proteomics Biomarker Investigation. Methods Mol Biol 2018; 1619:3-21. [PMID: 28674873 DOI: 10.1007/978-1-4939-7057-5_1] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Blood proteome analysis for biomarker discovery represents one of the most challenging tasks to be achieved through clinical proteomics due to the sample complexity, such as the extreme heterogeneity of proteins in very dynamic concentrations, and to the observation of proper sampling and storage conditions. Quantitative and qualitative proteomics profiling of plasma and serum could be useful both for the early detection of diseases and for the evaluation of pathological status. Two main sources of variability can affect the precision and accuracy of the quantitative experiments designed for biomarker discovery and validation. These sources are divided into two categories, pre-analytical and analytical, and are often ignored; however, they can contribute to consistent errors and misunderstanding in biomarker research. In this chapter, we review critical pre-analytical and analytical variables that can influence quantitative proteomics. According to guidelines accepted by proteomics community, we propose some recommendations and strategies for a proper proteomics analysis addressed to biomarker studies.
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Affiliation(s)
- Viviana Greco
- Proteomics and metabonomics unit, Fondazione Santa Lucia, IRCCS, Rome, Italy
| | - Cristian Piras
- Department of Veterinary Medicine, University of Milan, Milan, Italy
| | - Luisa Pieroni
- Proteomics and metabonomics unit, Fondazione Santa Lucia, IRCCS, Rome, Italy
| | - Andrea Urbani
- Proteomics and metabonomics unit, Fondazione Santa Lucia, IRCCS, Rome, Italy. .,Institute of Biochemistry and Clinical Biochemistry, Catholic University of Sacred Heart, Rome, Italy.
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Song HI, Hyeon T, Kim MS, Oh JY, Moon JH. Tracing the Origin of the Anomalous Matrix Suppression in Matrix-assisted Laser Desorption Ionization and Extending the Linear Dynamic Range During Analyte Quantification. B KOREAN CHEM SOC 2018. [DOI: 10.1002/bkcs.11368] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Hyo In Song
- Center for Nanoparticle Research; Institute for Basic Science (IBS); Seoul 08826 Korea
| | - Taeghwan Hyeon
- Center for Nanoparticle Research; Institute for Basic Science (IBS); Seoul 08826 Korea
| | - Myung Soo Kim
- Center for Nanoparticle Research; Institute for Basic Science (IBS); Seoul 08826 Korea
| | - Joo Yeon Oh
- Applied Surface Technology Ascend (ASTA); Suwon-si 07675 Korea
| | - Jeong Hee Moon
- Disease Target Structure Research Center; Korean Research Institute of Bioscience and Biotechnology (KRIBB); Daejeon 34141 Korea
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Ahmed A, Lim D, Choi CH, Kim S. Correlation between experimental data of protonation of aromatic compounds at (+) atmospheric pressure photoionization and theoretically calculated enthalpies. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2017; 31:1023-1030. [PMID: 28401729 DOI: 10.1002/rcm.7875] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Revised: 02/22/2017] [Accepted: 04/05/2017] [Indexed: 06/07/2023]
Abstract
RATIONALE The theoretical enthalpy calculated from the overall protonation reaction (electron transfer plus hydrogen transfer) in positive-mode (+) atmospheric-pressure photoionization (APPI) was compared with experimental results for 49 aromatic compounds. A linear relationship was observed between the calculated ΔH and the relative abundance of the protonated peak. The parameter gives reasonable predictions for all the aromatic hydrocarbon compounds used in this study. METHODS A parameter is devised by combining experimental MS data and high-level theoretical calculations. A (+) APPI Q Exactive Orbitrap mass spectrometer was used to obtain MS data for each solution. B3LYP exchange-correlation functions with the standard 6-311+G(df,2p) basis set was used to perform density functional theory (DFT) calculations. RESULTS All the molecules with ΔH <0 kcal/mol for the overall protonation reaction with toluene clusters produced protonated ions, regardless of the desolvation temperature. For molecules with ΔH >0, molecular ions were more abundant at typical APPI desolvation temperatures (300°C), while the protonated ions became comparable or dominant at higher temperatures (400°C). The toluene cluster size was an important factor when predicting the ionization behavior of aromatic hydrocarbon ions in (+) APPI. CONCLUSIONS The data used in this study clearly show that the theoretically calculated reaction enthalpy (ΔH) of protonation with toluene dimers can be used to predict the protonation behavior of aromatic compounds. When compounds have a negative ΔH value, the types of ions generated for aromatic compounds could be very well predicted based on the ΔH value. The ΔH can explain overall protonation behavior of compounds with ΔH values >0. Copyright © 2017 John Wiley & Sons, Ltd.
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Affiliation(s)
- Arif Ahmed
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
| | - Dongwon Lim
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
| | - Cheol Ho Choi
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
- Department of Chemistry, Green Nano Center, Daegu, 702-701, Republic of Korea
| | - Sunghwan Kim
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
- Department of Chemistry, Green Nano Center, Daegu, 702-701, Republic of Korea
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8
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Organic matrices, ionic liquids, and organic matrices@nanoparticles assisted laser desorption/ionization mass spectrometry. Trends Analyt Chem 2017. [DOI: 10.1016/j.trac.2017.01.012] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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9
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Kim S, Ahmed A. Protonation Sites of Aromatic Compounds in (+) Atmospheric Pressure Photoionization. B KOREAN CHEM SOC 2017. [DOI: 10.1002/bkcs.11058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Sunghwan Kim
- Department of Chemistry; Kyungpook National University; Daegu 702-701 Republic of Korea
- Department of Chemistry; Green Nano Center; Daegu 702-701 Republic of Korea
| | - Arif Ahmed
- Department of Chemistry; Kyungpook National University; Daegu 702-701 Republic of Korea
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10
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Shin D, Kim I, Paek J, Kim J. A Novel “Freeze Vacuum Drying” Crystallization Method Toward Quantitative MALDI-MS. B KOREAN CHEM SOC 2017. [DOI: 10.1002/bkcs.11046] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Dongwon Shin
- Department of Chemistry; Chungnam National University; Daejeon 305-764 Republic of Korea
| | - Inyoung Kim
- Department of Chemistry; Chungnam National University; Daejeon 305-764 Republic of Korea
| | - Jihyun Paek
- Department of Chemistry; Chungnam National University; Daejeon 305-764 Republic of Korea
| | - Jeongkwon Kim
- Department of Chemistry; Chungnam National University; Daejeon 305-764 Republic of Korea
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Park KM, Moon JH, Lee SH, Kim MS. Quantitative transfer of polar analytes on a solid surface to a liquid matrix in MALDI profiling. JOURNAL OF MASS SPECTROMETRY : JMS 2016; 51:1152-1156. [PMID: 27628951 DOI: 10.1002/jms.3886] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 08/29/2016] [Accepted: 09/12/2016] [Indexed: 06/06/2023]
Abstract
In profiling of a specimen by matrix-assisted laser desorption ionization (MALDI) using a solid matrix, the solvent of the matrix solution extracts an analyte(s). A quantitative profiling cannot be achieved if the solvent evaporates before the complete extraction of the analyte. The extraction can become more quantitative when a liquid matrix dissolved in a solvent is used, which remains a liquid even after the evaporation of the solvent. To check this, radii of an analyte circle (rA ), a matrix solution drop (rD ) and a liquid matrix (rM ) remaining after the solvent evaporation were controlled. Three types of samples were prepared, case A (rA , rD < rM ), case B (rD ≤ rM < rA ) and case C (rM < rD < rA ). In case A, the analyte amount in the matrix layer determined by MALDI was the same as the prepared amount inside the analyte circle. In case B, the analyte amount was the same as the amount inside the matrix circle. Only the analytes in contact with the liquid matrix layer, not more and not less, are transferred to the matrix layer. In case C, the analyte amount was greater than the amount inside the matrix circle, presumably because some of the analyte outside the matrix circle was dissolved by the solvent of the matrix solution. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Kyung Man Park
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Jeong Hee Moon
- Disease Target Structure Research Center, KRIBB, Daejeon, 305-806, Korea
| | - Seong Hoon Lee
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Myung Soo Kim
- Seoul National University Research Institute for Basic Sciences, Seoul, 151-747, Korea
- Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, 151-742, Korea
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12
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Quantitative profiling of O-glycans by electrospray ionization- and matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry after in-gel derivatization with isotope-coded 1-phenyl-3-methyl-5-pyrazolone. Anal Chim Acta 2016; 935:187-96. [DOI: 10.1016/j.aca.2016.06.032] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 06/02/2016] [Accepted: 06/16/2016] [Indexed: 11/19/2022]
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13
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Steven RT, Race AM, Bunch J. Probing the Relationship Between Detected Ion Intensity, Laser Fluence, and Beam Profile in Thin Film and Tissue in MALDI MSI. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:1419-1428. [PMID: 27206508 DOI: 10.1007/s13361-016-1414-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 04/14/2016] [Accepted: 04/23/2016] [Indexed: 06/05/2023]
Abstract
Matrix assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) is increasingly widely used to provide information regarding molecular location within tissue samples. The nature of the photon distribution within the irradiated region, the laser beam profile, and fluence, will significantly affect the form and abundance of the detected ions. Previous studies into these phenomena have focused on circular-core optic fibers or Gaussian beam profiles irradiating dried droplet preparations, where peptides were employed as the analyte of interest. Within this work, we use both round and novel square core optic fibers of 100 and 50 μm diameter to deliver the laser photons to the sample. The laser beam profiles were recorded and analyzed to quantify aspects of the photon distributions and their relation to the spectral data obtained with each optic fiber. Beam profiles with a relatively small number of large beam profile features were found to give rise to the lowest threshold fluence. The detected ion intensity versus fluence relationship was investigated, for the first time, in both thin films of α-cyano-4-hydroxycinnamic acid (CHCA) with phosphatidylcholine (PC) 34:1 lipid standard and in CHCA coated murine tissue sections for both the square and round optic fibers in continuous raster imaging mode. The fluence threshold of ion detection was found to occur at between ~14 and ~64 J/m(2) higher in tissue compared with thin film for the same lipid, depending upon the optic fiber employed. The image quality is also observed to depend upon the fluence employed during image acquisition. Graphical Abstract ᅟ.
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Affiliation(s)
- Rory T Steven
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory (NPL), Teddington, TW11 0LW, UK
| | - Alan M Race
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory (NPL), Teddington, TW11 0LW, UK
| | - Josephine Bunch
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory (NPL), Teddington, TW11 0LW, UK.
- School of Pharmacy, University of Nottingham, Nottingham, NG7 2RD, UK.
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Park KM, Yoon S, Moon JH, Lee SH, Kim MS. Use of Commercial MALDI-TOFs for Analyte Quantification by a Newly Invented Method. B KOREAN CHEM SOC 2016. [DOI: 10.1002/bkcs.10793] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Kyung Man Park
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Sohee Yoon
- Center for Nano-Bio measurement; Korea Research Institute of Standards and Science; Daejeon 305-340 Korea
| | - Jeong Hee Moon
- Functional Genomics Research Center; KRIBB; Daejeon 305-806 Korea
| | - Seong Hoon Lee
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Myung Soo Kim
- Seoul National University Research Institute for Basic Sciences; Seoul 151-747 Korea
- Center for Nanoparticle Research; Institute for Basic Science (IBS); Seoul 151-742 Korea
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15
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Ahn SH, Park KM, Moon JH, Lee SH, Kim MS. Preparation of Homogeneous Solid Samples for Reproducible and Quantitative MALDI. B KOREAN CHEM SOC 2016. [DOI: 10.1002/bkcs.10704] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Kyung Man Park
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Jeong Hee Moon
- Functional Genomics Research Center, KRIBB; Daejeon 305-806 Korea
| | - Seong Hoon Lee
- Department of Chemistry; Seoul National University; Seoul 151-747 Korea
| | - Myung Soo Kim
- Seoul National University Research Institute for Basic Sciences; Seoul 151-747 Korea
- Center for Nanoparticle Research, Institute for Basic Science (IBS); Seoul 151-742 Korea
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16
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Park KM, Moon JH, Kim JH, Song UT, Lee SH, Kim MS. Discovery of a solvent effect preventing quantitative profiling by matrix-assisted laser desorption/ionization and its treatment. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:386-392. [PMID: 26754131 DOI: 10.1002/rcm.7452] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 10/06/2015] [Accepted: 11/04/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE In analyte profiling by matrix-assisted laser desorption/ionization (MALDI), drawing a quantitative profile map is an outstanding problem. Recently, we developed a method to quantify an analyte by MALDI, which is needed to solve the problem. Another requirement for quantitative profiling is the quantitative sample-to-matrix analyte transfer, which is investigated in this work. METHODS MALDI-time-of-flight (TOF) spectra were acquired for samples produced by two methods. In one, a sample solution containing a matrix and an analyte was loaded with a pipet and dried. In the other, a sample was prepared by a consecutive process, i.e., loading-drying of an analyte solution followed by that of a matrix solution. Two different micro-spotters were used in the second method. Various mixtures of organic solvents with water were used to prepare matrix solutions. RESULTS The organic solvent, matrix, and analyte used in the study did not affect the analyte transfer efficiency, whereas it improved as the water content in the solvent increased. It also improved as the liquid droplet emitted by a micro-spotter got larger. Use of a more polar solvent or a larger droplet increases the contact time between a solution droplet and the sample surface, which seems to be responsible for the improvement in the transfer efficiency. CONCLUSIONS Sample-to-matrix analyte transfer occurred efficiently when polar solvents and/or large liquid droplets were used to produce solid samples for MALDI profiling with a micro-spotter. A long contact time between the sample surface and a matrix solution droplet is one of the requirements for quantitative profiling. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Kyung Man Park
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Jeong Hee Moon
- Functional Genomics Research Center, KRIBB, Daejeon, 305-806, Korea
| | - Jae Hyung Kim
- Analytical Instruments Division, Dong-il Shimadzu Corporation, Seoul, 135-010, Korea
| | - Un Tak Song
- Analytical Instruments Division, Dong-il Shimadzu Corporation, Seoul, 135-010, Korea
| | - Seong Hoon Lee
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Myung Soo Kim
- Seoul National University Research Institute for Basic Sciences, Seoul, 151-747, Korea
- Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, 151-742, Korea
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Kirmess KM, Knochenmuss R, Blanchard GJ, Kinsel GR. MALDI ionization mechanisms investigated by comparison of isomers of dihydroxybenzoic acid. JOURNAL OF MASS SPECTROMETRY : JMS 2016; 51:79-85. [PMID: 26757075 DOI: 10.1002/jms.3725] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2015] [Revised: 10/23/2015] [Accepted: 10/24/2015] [Indexed: 06/05/2023]
Abstract
Matrix-assisted laser desorption/ionization (MALDI) ion formation mechanisms were investigated by comparison of isomers of dihydroxybenzoic acid (DHB). These exhibit substantially different MALDI performance, the basis for which was not previously understood. Luminescence decay curves are used here to estimate excited electronic state properties relevant for the coupled chemical and physical dynamics (CPCD) model. With these estimates, the CPCD predictions for relative total ion and analyte ion yields are in good agreement with the data for the DHB isomers. Predictions of a thermal equilibrium model were also compared and found to be incompatible with the data. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Kristopher M Kirmess
- Department of Chemistry and Biochemistry, Southern Illinois University Carbondale, Carbondale, IL, 62901, USA
| | | | - Gary J Blanchard
- Department of Chemistry, Michigan State University, East Lansing, MI, 48824, USA
| | - Gary R Kinsel
- Department of Chemistry and Biochemistry, Southern Illinois University Carbondale, Carbondale, IL, 62901, USA
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18
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Moon JH, Park KM, Ahn SH, Lee SH, Kim MS. Investigations of Some Liquid Matrixes for Analyte Quantification by MALDI. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1657-1664. [PMID: 26122519 DOI: 10.1007/s13361-015-1202-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 05/16/2015] [Accepted: 05/19/2015] [Indexed: 06/04/2023]
Abstract
Sample inhomogeneity is one of the obstacles preventing the generation of reproducible mass spectra by MALDI and to their use for the purpose of analyte quantification. As a potential solution to this problem, we investigated MALDI with some liquid matrixes prepared by nonstoichiometric mixing of acids and bases. Out of 27 combinations of acids and bases, liquid matrixes could be produced from seven. When the overall spectral features were considered, two liquid matrixes using α-cyano-4-hydroxycinnamic acid as the acid and 3-aminoquinoline and N,N-diethylaniline as bases were the best choices. In our previous study of MALDI with solid matrixes, we found that three requirements had to be met for the generation of reproducible spectra and for analyte quantification: (1) controlling the temperature by fixing the total ion count, (2) plotting the analyte-to-matrix ion ratio versus the analyte concentration as the calibration curve, and (3) keeping the matrix suppression below a critical value. We found that the same requirements had to be met in MALDI with liquid matrixes as well. In particular, although the liquid matrixes tested here were homogeneous, they failed to display spot-to-spot spectral reproducibility unless the first requirement above was met. We also found that analyte-derived ions could not be produced efficiently by MALDI with the above liquid matrixes unless the analyte was sufficiently basic. In this sense, MALDI processes with solid and liquid matrixes should be regarded as complementary techniques rather than as competing ones.
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Affiliation(s)
- Jeong Hee Moon
- Functional Genomics Research Center, KRIBB, Daejeon, 305-806, Korea
| | - Kyung Man Park
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Seong Hoon Lee
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Myung Soo Kim
- Seoul National University Research Institute for Basic Sciences, Seoul, 151-747, Korea.
- Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, 151-742, Korea.
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19
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Ahn SH, Park KM, Moon JH, Lee SH, Kim MS. Acquisition of the depth profiles and reproducible mass spectra in matrix-assisted laser desorption/ionization of inhomogeneous samples. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:745-752. [PMID: 26406489 DOI: 10.1002/rcm.7157] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 12/22/2014] [Accepted: 01/25/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE In our previous analysis of the matrix-assisted laser desorption/ionization (MALDI) spectra of peptides, we treated their depth profiles in solid samples as homogeneous. Here, we wanted to determine if the reproducible MALDI spectra and linear calibration curves reported previously would be obtained even when the depth profiles were inhomogeneous. METHODS We derived a formula relating shot-number-dependent ion abundance data in temperature-controlled MALDI with the analyte depth profile in a solid sample. We prepared samples containing peptides, amino acids, and serotonin in α-cyano-4-hydroxycinnamic acid matrix by vacuum-drying and micro-spotting methods, recorded their MALDI spectra, and analyzed them with the aforementioned formula. RESULTS For the samples prepared by vacuum-drying, the analyte depth profiles were inhomogeneous and maximized at the sample surface. Although the MALDI spectra changed as the shot continued, their sum over the entire set of spectra acquired from a spot was reproducible. Similarly, a high-quality calibration curve could be obtained with the spectral data summed over the entire set. Depth profiles were homogeneous for samples prepared by micro-spotting. CONCLUSIONS A method has been developed to obtain a reproducible MALDI spectrum and a linear calibration curve for an analyte with an inhomogeneous depth profile in a solid sample.
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Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Kyung Man Park
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Jeong Hee Moon
- Medical Proteomics Research Center, KRIBB, Daejeon, 305-806, Korea
| | - Seong Hoon Lee
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Myung Soo Kim
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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20
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Ahn SH, Kang JW, Moon JH, Kim KP, Lee SH, Kim MS. Quick quantification of proteins by MALDI. JOURNAL OF MASS SPECTROMETRY : JMS 2015; 50:596-602. [PMID: 25800197 DOI: 10.1002/jms.3567] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 12/26/2014] [Accepted: 12/26/2014] [Indexed: 06/04/2023]
Abstract
Previously, we reported that the matrix-assisted laser desorption ionization spectrum of a peptide became reproducible when an effective temperature was held constant. Using a calibration curve drawn by plotting the peptide-to-matrix ion abundance ratio versus the peptide concentration in a solid sample, a peptide could be quantified without the use of any internal standard. In this work, we quantified proteins by quantifying their tryptic peptides with the aforementioned method. We modified the digestion process; e.g. disulfide bonds were not cleaved, so that hardly any reagent other than trypsin remained after the digestion process. This allowed the preparation of a sample by the direct mixing of a digestion mixture with a matrix solution. We also observed that the efficiency of the matrix-to-peptide proton transfer, as measured by its reaction quotient, was similar for peptides with arginine at the C-terminus. With the reaction quotient averaged over many such peptides, we could rapidly quantify proteins. Most importantly, no peptide standard, not to mention its isotopically labeled analog, was needed in this method.
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Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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21
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Bae YJ, Kim MS. A Thermal Mechanism of Ion Formation in MALDI. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2015; 8:41-60. [PMID: 26161971 DOI: 10.1146/annurev-anchem-081413-024102] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
An important recent discovery concerning the fundamentals of matrix-assisted laser desorption/ionization (MALDI) is that the abundance of each ion appearing in a spectrum is fixed, regardless of the experimental condition, when an effective temperature associated with the spectrum is fixed. We describe this phenomenon and the thermal picture for the ion formation in MALDI derived from it. Accepting that matrix-to-analyte proton transfer is in quasi-equilibrium as supported by experimental data, the above thermal determination occurs because the primary (matrix) ion formation processes are thermally governed. We propose that the abundances of the primary ions are limited by the autoprotolysis-recombination process regardless of how they are initially produced. Finally, we note that primary ion formation, secondary (analyte) ion formation, and their dissociations occur sequentially while the effective temperature of the matrix plume falls steadily due to cooling associated with expansion.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul 151-742, Korea;
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22
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Kirmess KM, Knochenmuss R, Blanchard GJ, Kinsel GR. Excited state dynamics in the matrix-assisted laser desorption/ionization matrix 2,4,6-trihydroxyacetophenone: evidence for triplet pooling charge separation reactions. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:2134-2140. [PMID: 25156603 DOI: 10.1002/rcm.7000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 07/25/2014] [Accepted: 07/26/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Excited state pooling reactions are a central part of some models of ultraviolet matrix-assisted laser desorption/ionization (MALDI) mechanisms. Evidence has been found for pooling in several matrix materials, but a recent report of pure exponential fluorescence decay at MALDI-relevant laser fluences suggested that 2,4,6-trihydroxy-acetophenone (THAP) may be an example of a matrix in which pooling does not occur (Lin et al., Rapid Commun. Mass Spectrom. 2014, 28, 77). However, those data were instrumentally limited in dynamic range and signal/noise ratio, and the conclusion does not take into account several aspects of THAP excited state dynamics. METHODS Using time-correlated single photon counting, and absorption and emission spectroscopies, the excited state dynamics of THAP are reexamined. RESULTS Like many other aromatic ketones and acetophenone, isolated THAP molecules undergo very efficient intersystem crossing. No fluorescence is observed in dilute solution. In the solid state, efficient fluorescence reappears, but is non-exponential even at very low excitation intensity. The solvent used for sample preparation was found to have a large effect on the spectra and decay curves. Needle-like crystals seem to be correlated with reduced intersystem crossing. CONCLUSIONS THAP solid state fluorescence is entirely due to intermolecular interactions. Activation of fluorescence, instead of quenching, is a clear indicator of delocalized excited state phenomena in THAP. Contrary to the conclusions of Lin et al., the greatly increased singlet lifetime in the solid state substantially increases the probability that pooling-type reactions are indeed involved in ionization processes. The sensitivity of fluorescence and phosphorescence on sample morphology appears to reflect changes in intermolecular interactions due to crystal packing. Pooling charge separation pathways based on known triplet-triplet ionization reactions of aromatic ketones are proposed.
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Affiliation(s)
- Kristopher M Kirmess
- Department of Chemistry and Biochemistry, Southern Illinois University at Carbondale, Carbondale, IL, 62901, USA
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23
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Knochenmuss R. Energetics and kinetics of thermal ionization models of MALDI. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1521-1527. [PMID: 24912435 DOI: 10.1007/s13361-014-0931-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/10/2014] [Accepted: 05/12/2014] [Indexed: 06/03/2023]
Abstract
Thermal models of ultraviolet MALDI ionization based on the polar fluid concept are re-examined. Key components are very high solvating power of the fluidized matrix and consequent low reaction-free energy, attainment of thermal equilibrium in the fluid, and negligible recombination losses. None of these are found to hold in a MALDI event. The reaction-free energy in the hot matrix must be near the gas phase value, ion formation is too slow to approach equilibrium, and geminate recombination of autoprotolysis pairs greatly increases the initial loss rate. The maximum thermal ion yield is estimated to be many orders of magnitude below experimental values.
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24
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Bae YJ, Park KM, Ahn SH, Moon JH, Kim MS. Spectral reproducibility and quantification of peptides in MALDI of samples prepared by micro-spotting. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1502-1505. [PMID: 24845358 DOI: 10.1007/s13361-014-0919-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2013] [Revised: 04/23/2014] [Accepted: 04/23/2014] [Indexed: 06/03/2023]
Abstract
Previously, we reported that MALDI spectra of peptides became reproducible when temperature was kept constant. Linear calibration curves derived from such spectral data could be used for quantification. Homogeneity of samples was one of the requirements. Among the three popular matrices used in peptide MALDI [i.e., α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (DHB), and sinapinic acid (SA)], homogeneous samples could be prepared by conventional means only for CHCA. In this work, we showed that sample preparation by micro-spotting improved the homogeneity for all three cases.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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25
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Park KM, Moon JH, Kim KP, Lee SH, Kim MS. Relative Quantification in Imaging of a Peptide on a Mouse Brain Tissue by Matrix-Assisted Laser Desorption Ionization. Anal Chem 2014; 86:5131-5. [DOI: 10.1021/ac500911x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Kyung M. Park
- Department
of Chemistry, Seoul National University, Seoul 151-747, Korea
| | - Jeong H. Moon
- Medical Proteomics Research Center, KRIBB, Daejeon 305-806, Korea
| | - Kwang P. Kim
- Department
of Applied Chemistry, Kyunghee University, Yongin 446-701, Korea
| | - Seong H. Lee
- Department
of Chemistry, Seoul National University, Seoul 151-747, Korea
| | - Myung S. Kim
- Department
of Chemistry, Seoul National University, Seoul 151-747, Korea
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26
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Bae YJ, Moon JH, Kim MS. Dual track time-of-flight mass spectrometry for peptide quantification with matrix-assisted laser desorption/ionization. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:787-792. [PMID: 24573810 DOI: 10.1002/rcm.6845] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 01/18/2014] [Accepted: 01/18/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Previously, we reported a method (Anal. Chem. 2012, 84, 10332) for peptide quantification based on matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). In the method, the peptide-to-matrix ion abundance ratio was utilized. Implementation of the method with a commercial MALDI-TOF can be somewhat inconvenient because matrix-derived ions are routinely deflected away to avoid detector saturation. A solution for this inconvenience is required. METHODS We installed a detector to acquire the TOF spectrum of the ions thrown away to avoid detector saturation. By sending the matrix- and peptide-derived ions along two different tracks and detecting them with different detectors, the inconvenience mentioned above could be avoided. RESULTS Excellent linearity of the calibration curves obtained by the dual track TOF spectrometry is demonstrated. The method also allows for the acquisition of the tandem mass spectrum of a selected peptide, which can be useful for its identification. CONCLUSIONS We devised the dual track MALDI-TOF MS method to avoid detector saturation and demonstrated that the quantification and identification of peptides can be performed simultaneously.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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27
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Bae YJ, Choe JC, Moon JH, Kim MS. Why do the abundances of ions generated by MALDI look thermally determined? JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:1807-1815. [PMID: 23990058 DOI: 10.1007/s13361-013-0717-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 07/23/2013] [Accepted: 07/23/2013] [Indexed: 06/02/2023]
Abstract
In a previous study (J. Mass Spectrom. 48, 299-305, 2013), we observed that the abundance of each ion in a matrix-assisted laser desorption ionization (MALDI) spectrum looked thermally determined. To find out the explanation for the phenomenon, we estimated the ionization efficiency and the reaction quotient (QA) for the autoprotolysis of matrix, M + M → [M + H](+) + [M - H](-), from the temperature-controlled laser desorption ionization spectra of α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB). We also evaluated the equilibrium constants (KA) for the autoprotolysis at various temperatures by quantum chemical calculation. Primary ion formation via various thermal models followed by autoprotolysis-recombination was compatible with the observations. The upper limit of the effective temperature of the plume where autoprotolysis-recombination occurs was estimated by equating QA with the calculated equilibrium constant. Figure ᅟ
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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28
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Knochenmuss R. MALDI ionization mechanisms: the coupled photophysical and chemical dynamics model correctly predicts 'temperature'-selected spectra. JOURNAL OF MASS SPECTROMETRY : JMS 2013; 48:998-1004. [PMID: 24078239 DOI: 10.1002/jms.3248] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 05/30/2013] [Accepted: 06/14/2013] [Indexed: 06/02/2023]
Abstract
A number of possible ultraviolet MALDI ionization mechanisms based on different fundamental phenomena have been proposed. Recently, it has been argued, based on 'temperature'-selected spectra, that photoionization models should be rejected in favor of thermal ones. Here, one non-thermal photoionization model, the coupled photophysical and chemical dynamics model, is shown to be fully consistent with the data.
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Affiliation(s)
- Richard Knochenmuss
- Research and Development, Tofwerk AG, Uttigenstrasse 22, 3600 Thun, Switzerland
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29
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Ahn SH, Bae YJ, Moon JH, Kim MS. Matrix Suppression as a Guideline for Reliable Quantification of Peptides by Matrix-Assisted Laser Desorption Ionization. Anal Chem 2013; 85:8796-801. [DOI: 10.1021/ac401967n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sung Hee Ahn
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Yong Jin Bae
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Jeong Hee Moon
- Medical
Proteomics Research Center, KRIBB, Daejeon 305-806, Korea
| | - Myung Soo Kim
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
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30
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Ahn SH, Park KM, Bae YJ, Kim MS. Efficient methods to generate reproducible mass spectra in matrix-assisted laser desorption ionization of peptides. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:868-876. [PMID: 23595259 DOI: 10.1007/s13361-013-0612-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2013] [Revised: 03/01/2013] [Accepted: 03/06/2013] [Indexed: 06/02/2023]
Abstract
In our previous matrix-assisted laser desorption ionization (MALDI) studies of peptides, we found that their mass spectra were virtually determined by the effective temperature in the early matrix plume, Tearly, when samples were rather homogeneous. This empirical rule allowed acquisition of quantitatively reproducible spectra. A difficulty in utilizing this rule was the complicated spectral treatment needed to get Tearly. In this work, we found another empirical rule that the total number of particles hitting the detector, or TIC, was a good measure of the spectral temperature and, hence, selection of spectra with the same TIC resulted in reproducible spectra. We also succeeded in obtaining reproducible spectra throughout a measurement by controlling TIC near a preset value through feedback adjustment of laser pulse energy. Both TIC selection and TIC control substantially reduced the shot-to-shot spectral variation in a spot, spot-to-spot variation in a sample, and even sample-to-sample variation in MALDI using α-cyano-4-hydroxycinnamic acid or 2,5-dihydroxybenzoic acid as matrix. Based on the utilization of acquired data, TIC control was more efficient than TIC selection by an order of magnitude. Both techniques produced calibration curves with excellent linearity, suggesting their utility in quantification of peptides.
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Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul, 151-742, Korea
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31
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Knochenmuss R. MALDI and Related Methods: A Solved Problem or Still a Mystery? Mass Spectrom (Tokyo) 2013; 2:S0006. [PMID: 24349925 DOI: 10.5702/massspectrometry.s0006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Accepted: 01/22/2013] [Indexed: 11/23/2022] Open
Abstract
MALDI ionization mechanisms remain a topic of controversy. Some of the major modern models are compared, with emphasis on those of the author. Primary formation, secondary reaction, and loss mechanisms are considered.
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Park KM, Ahn SH, Bae YJ, Kim MS. Efficiency of Gas-Phase Ion Formation in Matrix-Assisted Laser Desorption Ionization with 2,5-Dihydroxybenzoic Acid as Matrix. B KOREAN CHEM SOC 2013. [DOI: 10.5012/bkcs.2013.34.3.907] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Ahn SH, Park KM, Bae YJ, Kim MS. Quantitative reproducibility of mass spectra in matrix-assisted laser desorption ionization and unraveling of the mechanism for gas-phase peptide ion formation. JOURNAL OF MASS SPECTROMETRY : JMS 2013; 48:299-305. [PMID: 23494784 DOI: 10.1002/jms.3155] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 12/07/2012] [Accepted: 12/11/2012] [Indexed: 06/01/2023]
Abstract
In a previous study on matrix-assisted laser desorption ionization (MALDI) of peptides using α-cyano-4-hydroxycinnamic acid (CHCA) as a matrix, we found that the patterns of single-shot spectra obtained under different experimental conditions became similar upon temperature selection. In this paper, we report that absolute ion abundances are also similar in temperature-selected MALDI spectra, even when laser fluence is varied. The result that has been obtained using CHCA and 2,5-dihydroxybenzoic acid as matrices is in disagreement with the hypothesis of laser-induced ionization of matrix as the mechanism for primary ion formation in MALDI. We also report that the total number of ions in such a spectrum is unaffected by the identity, concentration and number of analytes, i.e. it is the same as that in the spectrum of pure matrix. We propose that the generation of gas-phase ions in MALDI can be explained in terms of two thermal reactions, i.e. the autoprotolysis of matrix molecules and the matrix-to-analyte proton transfer, both of which are in quasi-equilibrium in the early matrix plume.
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Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul 151-742, Korea
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34
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Yasuda A, Ishimaru T, Nishihara S, Sakai M, Kawasaki H, Arakawa R, Shigeri Y. A thiophene-containing compound as a matrix for matrix-assisted laser desorption/ ionization mass spectrometry and the electrical conductivity of matrix crystals. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2013; 19:29-37. [PMID: 23841223 DOI: 10.1255/ejms.1215] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The electrical conductivity of the matrix crystal might be a new factor to enhance matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) sensitivity. In MALDI-MS, several compounds are used as a standard matrix. Utilization of such compounds is based on an a posteriori approach, but there is no theoretical guidance for selecting a matrix. In an attempt to further understand performance in MALDI-MS, we utilized peptide detection for random screening of a chemical library (12,383 compounds) for compounds with matrix functions in MALDI-MS. A lot of thiophene compounds were found to be a matrix, in which 2-[5-(2,4-dichlorobenzoyl)-2-thienyl] acetic acid (DCBTA) provided an important clue to measure the electrical conductivity of the matrix crystal, because the structure of DCBTA is analogous to conductive polymers and organic solar cells. Most of the crystals of standard matrices, such as alpha-cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid [sinapinic acid, (SA)], and DCBTA showed electrical conductivity, whereas the conductivity of crystal was not observed in 2,5-dihydroxybenzoic acid (2,5-DHB). On the other hand, super-DHB using 2-hydroxy-5-methoxybenzoic acid [5-methoxysalicylic acid, (MSA)] as an additive to 2,5-DHB, improved the electrical conductivity of the crystal, that followed the enhancement of peak intensity in MS spectrum. These observations might indicate that the electrical conductivity of matrix crystals is a key consideration in obtaining efficient MALDI performance.
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Affiliation(s)
- Akikazu Yasuda
- Health Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Midorigaoka, Ikeda, Osaka 563-8577, Japan
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35
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Park KM, Bae YJ, Ahn SH, Kim MS. A Simple Method for Quantification of Peptides and Proteins by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry. Anal Chem 2012; 84:10332-7. [DOI: 10.1021/ac302807u] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Kyung Man Park
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Yong Jin Bae
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Sung Hee Ahn
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Myung Soo Kim
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
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