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Schmidt M, Irsig R, Duca D, Peltz C, Passig J, Zimmermann R. Laser-Pulse-Length Effects in Ultrafast Laser Desorption. Anal Chem 2023; 95:18776-18782. [PMID: 38086534 PMCID: PMC10753527 DOI: 10.1021/acs.analchem.3c03558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 11/02/2023] [Accepted: 11/09/2023] [Indexed: 12/27/2023]
Abstract
Shortening the laser pulse length opens up new opportunities for laser desorption (LD) of molecules, with benefits for mass spectrometry (MS) sampling and ionization. The capability to ablate any material without the need for an absorbing matrix and the decrease of thermal damage and molecular fragmentation has promoted various applications with very different parameters and postionization techniques. However, the key issues of the optimum laser pulse length and intensity to achieve efficient and gentle desorption of molecules for postionization in MS are not resolved, although these parameters determine the costs and complexity of the required laser system. Here, we address this research gap with a systematic study on the effect of the pulse length on the LD of molecules. Keeping all other optical and ionization parameters constant, we directly compared the pulses in the femtosecond, picosecond, and nanosecond range with respect to LD-induced fragmentation and desorption efficiency. To represent real-world applications, we investigated the LD of over-the-counter medicaments naproxen and ibuprofen directly from tablets as well as the LD of retene and ship emission aerosols from a quartz filter. With our study design, we excluded interfering effects on fragmentation and LD efficiency from, for example, collisional cooling or postionization by performing the experiments in vacuum with resonance-enhanced multiphoton ionization as the postionization technique. Regarding LD-induced fragmentation, we already found benefits for the picosecond pulses. However, the efficiency of LD was found to continuously increase with decreasing pulse length, pointing to the application potential of ultrashort pulses in trace analytics. Because many interfering effects beyond the LD pulse length could be excluded in the experiment, our results may be directly transferable to the LD applied in other techniques.
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Affiliation(s)
- Marco Schmidt
- Joint
Mass Spectrometry Centre, Analytical Chemistry, University of Rostock, 18059 Rostock, Germany
- Comprehensive
Molecular Analytics (CMA) Cooperation Group, Helmholtz Centre Munich, 81379 Munich, Germany
- Department
Life, Light & Matter, University of
Rostock, 18059 Rostock, Germany
| | - Robert Irsig
- Department
Life, Light & Matter, University of
Rostock, 18059 Rostock, Germany
- Photonion
GmbH, 19061 Schwerin, Germany
| | - Dumitru Duca
- Joint
Mass Spectrometry Centre, Analytical Chemistry, University of Rostock, 18059 Rostock, Germany
- Comprehensive
Molecular Analytics (CMA) Cooperation Group, Helmholtz Centre Munich, 81379 Munich, Germany
- Department
Life, Light & Matter, University of
Rostock, 18059 Rostock, Germany
| | - Christian Peltz
- Institute
for Physics, University of Rostock, 18059 Rostock, Germany
| | - Johannes Passig
- Joint
Mass Spectrometry Centre, Analytical Chemistry, University of Rostock, 18059 Rostock, Germany
- Comprehensive
Molecular Analytics (CMA) Cooperation Group, Helmholtz Centre Munich, 81379 Munich, Germany
- Department
Life, Light & Matter, University of
Rostock, 18059 Rostock, Germany
| | - Ralf Zimmermann
- Joint
Mass Spectrometry Centre, Analytical Chemistry, University of Rostock, 18059 Rostock, Germany
- Comprehensive
Molecular Analytics (CMA) Cooperation Group, Helmholtz Centre Munich, 81379 Munich, Germany
- Department
Life, Light & Matter, University of
Rostock, 18059 Rostock, Germany
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2
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Asakawa D, Hosokai T, Nakayama Y. Experimental and Theoretical Investigation of MALDI In-Source Decay of Peptides with a Reducing Matrix: What Is the Initial Fragmentation Step? JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022; 33:1011-1021. [PMID: 35587880 DOI: 10.1021/jasms.2c00066] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) with a reducing matrix is believed to be initiated by hydrogen transfer from the matrix to the peptide. Several new matrices have recently been developed to achieve more efficient MALDI-ISD. In particular, the use of matrices containing aniline groups facilitates MALDI-ISD to a greater extent than that of matrices containing phenol groups, although the N-H bond in aniline is stronger than the O-H bond in phenol. In this study, photoelectron yield spectroscopy of matrix solids revealed that conversion of the phenol group to the aniline group decreased the ionization energy of the matrix solids. Crucially, the use of a matrix with lower ionization energy has been found to result in efficient cleavage at N-Cα and disulfide bonds by MALDI-ISD. Therefore, electron association with the peptide rather than the fragmentation mechanism involving hydrogen atom attachment is proposed as the initial step of the MALDI-ISD process. In this mechanism, electron transfer from the reducing matrix to the peptide produces a peptide anion radical, which provides either a [cn + H]/[zm]• or [an]•/[ym + H] fragment pair. Fragmentation of the peptide anion radical strongly depends on the gas-phase acidity of the matrix used. Subsequently, the resultant fragments/radicals underwent a reaction in the MALDI plume, producing observable even-electron ions. Consequently, MALDI-ISD fragments are observed as both positive and negative ions, even though MALDI-ISD with a reducing matrix involves fragmentation of peptide anion radicals. The proposed mechanism is suitable for obtaining a better understanding of the MALDI-ISD process.
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Affiliation(s)
- Daiki Asakawa
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
| | - Takuya Hosokai
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
- Department of Pure and Applied Chemistry, Tokyo University of Science, Noda, Chiba 278-8510, Japan
| | - Yasuo Nakayama
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
- Department of Pure and Applied Chemistry; Division of Colloid and Interface Science; Research Group for Advanced Energy Conversion, Tokyo University of Science, Noda 278-8510, Japan
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3
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Asakawa D. Ultraviolet-Laser-Induced Electron Transfer from Peptides to an Oxidizing Matrix: Study of the First Step of MALDI In-Source Decay Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2020; 31:1918-1926. [PMID: 32687357 DOI: 10.1021/jasms.0c00186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Although the N-H bond in peptide backbones is stronger than the C-H bond, hydrogen abstraction from the amide nitrogen is considered to be the initial step in the Cα-C bond cleavage of peptide backbones by matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) when using an oxidizing matrix. MALDI-ISD induces Cα-C bond cleavage in most amino acid residues, whereas the N-terminal sides of proline (Pro) residues preferentially undergo peptide bond cleavage, which cannot be explained by the previously proposed mechanism involving hydrogen abstraction from peptides. To explain the whole MALDI-ISD process, electron abstraction from peptides by the oxidizing matrix is proposed as the initial step in the MALDI-ISD process. The electron abstraction occurs from either nitrogen or oxygen in the peptide backbone and induces the cleavage of both Cα-C and N-H bonds in most amino acid residues, except for those on the N-terminal sides of Pro residues. Electron abstraction from the Pro residues induces the cleavage of both peptide and Cα-C bonds, which is consistent with MALDI-ISD experimental results. The electron transfer from the peptide to the oxidizing matrix occurs simultaneously with the formation of matrix ions, which is considered to be the initial ion formation process in MALDI. The resultant peptide radical cation produces protonated and neutral molecules/radicals, which undergo subsequent ion-molecule reactions in the MALDI plume, finally yielding the ions that are observed in MALDI-ISD spectrum. As a result, the fragment ions formed by MALDI-ISD are observed as both positive and negative ions.
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Affiliation(s)
- Daiki Asakawa
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
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4
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Shirota T, Hoshina K. Generation and Propagation of MALDI Ion Packets Probed by Sheet-Like Nanosecond UV Laser Light. ACTA ACUST UNITED AC 2018; 7:A0071. [PMID: 30588414 PMCID: PMC6305245 DOI: 10.5702/massspectrometry.a0071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Accepted: 11/09/2018] [Indexed: 11/29/2022]
Abstract
A sheet-like ultraviolet (UV) probe laser is used to investigate the ejection and propagation of ion packets of matrix CHCA, which are produced by matrix-assisted laser desorption and ionization (MALDI). Laser irradiation of the expanding MALDI plume induced photodissociation of the CHCA-related ions, which existed in a sheet-like volume, leading to their absence in their MALDI signal profiles. The MALDI spectra were measured under varying conditions: the temporal delay of the lasers and the distance of the sheet-like probe laser from the MALDI sample surface. It was found that the center of the (CHCA)H+ packets were ejected at 46±11 ns after MALDI laser irradiation, while the (CHCA)2H+ packets were ejected at 64±12 ns, regardless of the magnitude of acceleration static high-voltage in 3.5–5.5 kV. This suggests that (CHCA)2H+ is formed by a proton transfer reaction from (CHCA)H+ to (CHCA)2 in the heated condensed phase and/or near the surface. This study represents the first experimental determination of ion ejection time in the MALDI process, which is also applicable to other species in the MALDI plume.
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Affiliation(s)
- Tatsuro Shirota
- Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, 265-1 Higashijima, Akiha-ku, Niigata 956-8603, Japan
| | - Kennosuke Hoshina
- Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, 265-1 Higashijima, Akiha-ku, Niigata 956-8603, Japan
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5
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Biomolecular Clusters Distribution up to Mega Dalton Region Using MALDI-Quadrupole Ion Trap Mass Spectrometer. Int J Mol Sci 2018; 19:ijms19092789. [PMID: 30227603 PMCID: PMC6164314 DOI: 10.3390/ijms19092789] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2018] [Revised: 09/01/2018] [Accepted: 09/14/2018] [Indexed: 11/17/2022] Open
Abstract
We present the first report on complete cluster distributions of cytochrome c (molecular weight of 12.4 kDa) and bovine serum albumin ((BSA), molecular weight of 66.4 kDa) with mass-to-charge ratio (m/z) reaching 350,000 and 1,400,000, respectively, by matrix-assisted laser desorption/ionization (MALDI). Large cluster distributions of the analytes were measured by our homemade frequency-scanned quadrupole ion trap (QIT) mass spectrometer with a charge detector. To our knowledge, we report the highest m/z clusters of these two biomolecules. The quantitative results indicate that large clusters ions of cytochrome c and BSA follow the power law (r2 > 0.99) with cluster size distribution, which provides experimental evidence for the laser ablation studies of MALDI.
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6
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New insights into mechanisms of material ejection in MALDI mass spectrometry for a wide range of spot sizes. Sci Rep 2018; 8:7755. [PMID: 29773805 PMCID: PMC5958139 DOI: 10.1038/s41598-018-25946-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 04/25/2018] [Indexed: 01/22/2023] Open
Abstract
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is widely used for the analysis of large biomolecules in numerous applications. The technique utilizes nanosecond-long laser pulses at various spot sizes to eject and ionize large molecules embedded in a highly absorptive chemical matrix. Despite the methods name, ‘molecular desorption’ from the matrix crystal surface is not the sole mechanism discussed for material ejection in MALDI, but additional ablation of larger clusters has been reported. Here we present results on the influence of laser fluence and spot size on the mechanisms of the initial material ejection in MALDI and subsequent plume development. We used a laser-based postionization (MALDI-2) as well as a complementary photoacoustic method to monitor the material ejection step. The photoacoustic data reveal a quasi-thermal sublimation process up to a transition fluence. Above this threshold fluence additional ablation processes are observed. Complementary investigations on plume dynamics by MALDI-2 showed an ejection of predominantly fast particles for desorption conditions while ablation produces considerably slower ejecta. Additionally the presented results revealed a peculiar influence of the spot size on analyte fragmentation as well as plume development and allows for new insights into the unexplained spot size effect reported for MALDI.
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7
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Lai YH, Wang YS. Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Mechanistic Studies and Methods for Improving the Structural Identification of Carbohydrates. Mass Spectrom (Tokyo) 2017; 6:S0072. [PMID: 28959517 PMCID: PMC5610957 DOI: 10.5702/massspectrometry.s0072] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Accepted: 08/03/2017] [Indexed: 12/21/2022] Open
Abstract
Although matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is one of the most widely used soft ionization methods for biomolecules, the lack of detailed understanding of ionization mechanisms restricts its application in the analysis of carbohydrates. Structural identification of carbohydrates achieved by MALDI mass spectrometry helps us to gain insights into biological functions and pathogenesis of disease. In this review, we highlight mechanistic details of MALDI, including both ionization and desorption. Strategies to improve the ion yield of carbohydrates are also reviewed. Furthermore, commonly used fragmentation methods to identify the structure are discussed.
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8
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Zou J, Wu C, Robertson WD, Zhigilei LV, Miller RJD. Molecular dynamics investigation of desorption and ion separation following picosecond infrared laser (PIRL) ablation of an ionic aqueous protein solution. J Chem Phys 2017; 145:204202. [PMID: 27908131 DOI: 10.1063/1.4967164] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Molecular dynamics simulations were performed to characterize the ablation process induced by a picosecond infrared laser (PIRL) operating in the regime of desorption by impulsive vibrational excitation (DIVE) of a model peptide (lysozyme)/counter-ion system in aqueous solution. The simulations were performed for ablation under typical experimental conditions found within a time-of-flight mass spectrometer (TOF-MS), that is in vacuum with an applied electric field (E = ± 107 V/m), for up to 2 ns post-ablation and compared to the standard PIRL-DIVE ablation condition (E = 0 V/m). Further, a simulation of ablation under an extreme field condition (E = 1010 V/m) was performed for comparison to extend the effective dynamic range of the effect of the field on charge separation. The results show that the plume dynamics were retained under a typical TOF-MS condition within the first 1 ns of ablation. Efficient desorption was observed with more than 90% of water molecules interacting with lysozyme stripped off within 1 ns post-ablation. The processes of ablation and desolvation of analytes were shown to be independent of the applied electric field and thus decoupled from the ion separation process. Unlike under the extreme field conditions, the electric field inside a typical TOF-MS was shown to modify the ions' motion over a longer time and in a soft manner with no enhancement to fragmentation observed as compared to the standard PIRL-DIVE. The study indicates that the PIRL-DIVE ablation mechanism could be used as a new, intrinsically versatile, and highly sensitive ion source for quantitative mass spectrometry.
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Affiliation(s)
- J Zou
- Departments of Chemistry and Physics, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada
| | - C Wu
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904-4745, USA
| | - W D Robertson
- Max Plank Institute for the Structure and Dynamics of Matter, 149 Luruper Chaussee, 27761 Hamburg, Germany
| | - L V Zhigilei
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904-4745, USA
| | - R J D Miller
- Departments of Chemistry and Physics, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada
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9
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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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10
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Hieke A. Suppression of unimolecular decay of laser desorbed peptide and protein ions by entrainment in rarefied supersonic gas jets under weak electric fields. J Chem Phys 2014; 140:034201. [PMID: 25669372 DOI: 10.1063/1.4861040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Unimolecular decay of sample ions imposes a limit on the usable laser fluence in matrix-assisted laser desorption/ionization (MALDI) ion sources. Traditionally, some modest degree of collisional sample ion cooling has been achieved by connecting MALDI ion sources directly to gas-filled radio frequency (RF) multipoles. It was also discovered in the early 1990s that gas-filled RF multipoles exhibit increased ion transmission efficiency due to collisional ion focusing effects. This unexpected experimental finding was later supported by elementary Monte Carlo simulations. Both experiments and simulations assumed a resting background gas with typical pressures of the order of 1 Pa. However, considerable additional improvements can be achieved if laser desorbed sample ions are introduced immediately after desorption, still within the ion source, in an axisymmetric rarefied supersonic gas jet with peak pressure of the order of 100 Pa and flow velocities >300 m/s, and under weak electric fields. We describe here the design principle and report performance data of an ion source coined "MALDI-2," which incorporates elements of both rarefied aerodynamics and particle optics. Such a design allows superb suppression of metastable fragmentation due to rapid collisional cooling in <10 μs and nearly perfect injection efficiency into the attached RF ion guide, as numerous experiments have confirmed.
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Affiliation(s)
- Andreas Hieke
- Department of Structural Biology, School of Medicine, Stanford University, 299 Campus Drive West, Fairchild Building, 148, Stanford, California 94305-5126, USA
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11
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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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12
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Melvin Blaze M, Takahashi LK, Zhou J, Ahmed M, Gasper GL, Pleticha FD, Hanley L. Brominated tyrosine and polyelectrolyte multilayer analysis by laser desorption vacuum ultraviolet postionization and secondary ion mass spectrometry. Anal Chem 2011; 83:4962-9. [PMID: 21548612 PMCID: PMC3115520 DOI: 10.1021/ac200693h] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The small molecular analyte 3,5-dibromotyrosine (Br(2)Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br(2)Y were analyzed by laser desorption postionization-mass spectrometry (LDPI-MS). LDPI-MS using a 7.87 eV laser and tunable 8-12.5 eV synchrotron vacuum ultraviolet (VUV) radiation found that desorption of clusters from Br(2)Y films allowed detection by ≤8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br(2)Y to be ~8.3 ± 0.1 eV and further indicated that the lower ionization energies of clusters permitted their detection at ≤8 eV photon energies. However, single photon ionization could only detect Br(2)Y adsorbed within PEMs when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi(3)(+) secondary ion mass spectrometry (SIMS), with the negative ion spectra showing strong parent ion signal which complemented that observed by LDPI-MS. However, the negative ion SIMS appeared strongly dependent on the high electron affinity of this specific analyte and the analyte's condensed phase environment.
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Affiliation(s)
- M.T. Melvin Blaze
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607
| | - Lynelle K. Takahashi
- Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Jia Zhou
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
| | - Gerald L. Gasper
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607
| | - F. Douglas Pleticha
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607
| | - Luke Hanley
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607
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Gasper GL, Takahashi LK, Zhou J, Ahmed M, Moore JF, Hanley L. Laser desorption postionization mass spectrometry of antibiotic-treated bacterial biofilms using tunable vacuum ultraviolet radiation. Anal Chem 2011; 82:7472-8. [PMID: 20712373 DOI: 10.1021/ac101667q] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Laser desorption postionization mass spectrometry (LDPI-MS) with 8.0-12.5 eV vacuum ultraviolet synchrotron radiation is used to single photon ionize antibiotics and extracellular neutrals that are laser desorbed both from neat and intact bacterial biofilms. Neat antibiotics are optimally detected using 10.5 eV LDPI-MS but can be ionized using 8.0 eV radiation, in agreement with prior work using 7.87 eV LDPI-MS. Tunable vacuum ultraviolet radiation also postionizes laser desorbed neutrals of antibiotics and extracellular material from within intact bacterial biofilms. Different extracellular material is observed by LDPI-MS in response to rifampicin or trimethoprim antibiotic treatment. Once again, 10.5 eV LDPI-MS displays the optimum trade-off between improved sensitivity and minimum fragmentation. Higher energy photons at 12.5 eV produce significant parent ion signal, but fragment intensity and other low mass ions are also enhanced. No matrix is added to enhance desorption, which is performed at peak power densities insufficient to directly produce ions, thus allowing observation of true VUV postionization mass spectra of antibiotic treated biofilms.
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Affiliation(s)
- Gerald L Gasper
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, USA
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