1
|
Qi Y, Fu P, Volmer DA. Analysis of natural organic matter via fourier transform ion cyclotron resonance mass spectrometry: an overview of recent non-petroleum applications. MASS SPECTROMETRY REVIEWS 2022; 41:647-661. [PMID: 32412674 DOI: 10.1002/mas.21634] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 11/22/2019] [Indexed: 06/11/2023]
Abstract
Among the different techniques for mass analysis, ultra-high-resolution Fourier transform ion cyclotron resonance (FTICR) is the method of choice for highly complex samples, as it offers unrivaled mass accuracy and resolving power, combined with a high degree of flexibility in hybrid instruments as well as for ion activation techniques. FTICR instruments are readily embraced by the biological and biomedical research communities and applied over a wide range of applications for the analysis of biomolecules such as carbohydrates, lipids, nucleic acids, and proteins. In the field of natural organic matter (NOM) analysis, petroleum-related studies currently dominate FTICR-MS applications. Recently, however, there is a growing interest in developing high-performance MS methods for the characterization of NOM samples from natural aquatic and terrestrial environments. Here, we present an overview of FTICR-MS techniques for complex, non-petroleum NOM samples, including data analysis and novel tandem mass spectrometry (MS/MS) methods for structural classifications. © 2020 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd.
Collapse
Affiliation(s)
- Yulin Qi
- Institute of Surface-Earth System Science, Tianjin University, Tianjin, China
- Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Pingqing Fu
- Institute of Surface-Earth System Science, Tianjin University, Tianjin, China
| | - Dietrich A Volmer
- Department of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany
| |
Collapse
|
2
|
Zenaidee MA, Lantz C, Perkins T, Jung W, Ogorzalek Loo RR, Loo JA. Internal Fragments Generated by Electron Ionization Dissociation Enhance Protein Top-Down Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2020; 31:1896-1902. [PMID: 32799534 PMCID: PMC7485267 DOI: 10.1021/jasms.0c00160] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Top-down proteomics by mass spectrometry (MS) involves the mass measurement of an intact protein followed by subsequent activation of the protein to generate product ions. Electron-based fragmentation methods like electron capture dissociation and electron transfer dissociation are widely used for these types of analyses. Recently, electron ionization dissociation (EID), which utilizes higher energy electrons (>20 eV) has been suggested to be more efficient for top-down protein fragmentation compared to other electron-based dissociation methods. Here, we demonstrate that the use of EID enhances protein fragmentation and subsequent detection of protein fragments. Protein product ions can form by either single cleavage events, resulting in terminal fragments containing the C-terminus or N-terminus of the protein, or by multiple cleavage events to give rise to internal fragments that include neither the C-terminus nor the N-terminus of the protein. Conventionally, internal fragments have been disregarded, as reliable assignments of these fragments were limited. Here, we demonstrate that internal fragments generated by EID can account for ∼20-40% of the mass spectral signals detected by top-down EID-MS experiments. By including internal fragments, the extent of the protein sequence that can be explained from a single tandem mass spectrum increases from ∼50 to ∼99% for 29 kDa carbonic anhydrase II and 8.6 kDa ubiquitin. When searching for internal fragments during data analysis, previously unassigned peaks can be readily and accurately assigned to confirm a given protein sequence and to enhance the utility of top-down protein sequencing experiments.
Collapse
Affiliation(s)
- Muhammad A. Zenaidee
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095
| | - Carter Lantz
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095
| | - Taylor Perkins
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095
| | - Wonhyuek Jung
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095
| | - Rachel R. Ogorzalek Loo
- Department of Biological Chemistry, University of California-Los Angeles, Los Angeles, CA 90095
| | - Joseph A. Loo
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095
- Department of Biological Chemistry, University of California-Los Angeles, Los Angeles, CA 90095
| |
Collapse
|
3
|
Jiang J, Serago JJ, Torres K, Rapp E, Savage PE. Fate of iron during hydrothermal liquefaction of hemin. J Supercrit Fluids 2020. [DOI: 10.1016/j.supflu.2019.104705] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
4
|
Lopez-Clavijo AF, Griffiths RL, Goodwin RJA, Cooper HJ. Liquid Extraction Surface Analysis (LESA) Electron-Induced Dissociation and Collision-Induced Dissociation Mass Spectrometry of Small Molecule Drug Compounds. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:2218-2226. [PMID: 30151679 DOI: 10.1007/s13361-018-2042-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Revised: 07/26/2018] [Accepted: 07/27/2018] [Indexed: 06/08/2023]
Abstract
Here, we present liquid extraction surface analysis (LESA) coupled with electron-induced dissociation (EID) mass spectrometry in a Fourier-transform ion cyclotron resonance mass spectrometer for the analysis of small organic pharmaceutical compounds directly from dosed tissue. First, the direct infusion electrospray ionisation EID and collision-induced dissociation (CID) behaviour of erlotinib, moxifloxacin, clozapine and olanzapine standards were compared. EID mass spectra were also compared with experimental or reference electron impact ionisation mass spectra. The results show that (with the exception of erlotinib) EID and CID result in complementary fragment ions. Subsequently, we performed LESA EID MS/MS and LESA CID MS/MS on singly charged ions of moxifloxacin and erlotinib extracted from a thin tissue section of rat kidney from a cassette-dosed animal. Both techniques provided structural information, with the majority of peaks observed for the drug standards also observed for the tissue-extracted species. Overall, these results demonstrate the feasibility of LESA EID MS/MS of drug compounds from dosed tissue and extend the number of molecular structures for which EID behaviour has been determined. Graphical Abstract ᅟ.
Collapse
Affiliation(s)
| | - Rian L Griffiths
- School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK
| | - Richard J A Goodwin
- Pathology, Drug Safety & Metabolism, IMED Biotech Unit, AstraZeneca, Darwin Building, Cambridge Science Park, Milton Road, Cambridge, CB4 0WG, UK
| | - Helen J Cooper
- School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK.
| |
Collapse
|
5
|
Wong YLE, Chen X, Li W, Wang Z, Hung YLW, Wu R, Chan TWD. Differentiation of Isomeric Ginsenosides by Using Electron-Induced Dissociation Mass Spectrometry. Anal Chem 2016; 88:5590-4. [PMID: 27181402 DOI: 10.1021/acs.analchem.6b00908] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Current phytochemical research on ginsengs focuses on the structural characterization and isomer differentiation of ginsenosides. In this Letter, electron-induced dissociation (EID) was initially investigated by analyzing isomeric ginsenosides. EID provided more structural information on their differentiation than collision-induced dissociation (CID) did. Glycosyl group migration previously observed in the CID of oligosaccharide ions could also be found in the EID of protonated Rg1. This rearrangement reaction would show substantial ambiguities in differentiating Rg1 from Rf. Although other charge carriers could alleviate this problem, the use of EID in dissociating deprotonated ginsenoside ions was superior to other techniques in terms of eliminating glycosyl group migration and generating diagnostic fragment ions for the differentiation of structural isomers. This study demonstrates a potential method to analyze natural products and thus help discover and evaluate novel compounds.
Collapse
Affiliation(s)
- Y-L Elaine Wong
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China
| | - Xiangfeng Chen
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China.,Key Laboratory for TCM Quality Control Technology, Shandong Analysis and Test Centre, Shandong Academy of Sciences , Jinan, Shandong, 250014, P. R. China
| | - Wan Li
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China
| | - Ze Wang
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China
| | - Y-L Winnie Hung
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China
| | - Ri Wu
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China
| | - T-W Dominic Chan
- Department of Chemistry, The Chinese University of Hong Kong , Hong Kong SAR, P. R. China
| |
Collapse
|
6
|
Qi Y, Volmer DA. Structural analysis of small to medium-sized molecules by mass spectrometry after electron-ion fragmentation (ExD) reactions. Analyst 2016; 141:794-806. [PMID: 26725919 DOI: 10.1039/c5an02171e] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron capture dissociation (ECD) is a tandem mass spectrometry (MS/MS) method that utilizes the interaction of ions and electrons. Its unique ability to preserve labile bonds distinguishes it from conventional threshold-based MS/MS methods, the most important of which is collision-induced dissociation (CID). During the last decade, ECD has opened up several new venues in protein analyses, for example top-down sequencing, identification of post-translational modifications, and characterization of protein-protein interactions. In recent years, a number of related dissociation techniques, so-called ExD techniques, particularly electron transfer dissociation (ETD), electron detachment dissociation (EDD), electron induced dissociation (EID), and negative electron transfer dissociation (NETD), have emerged and have extended the application range of ion-electron dissociations further. Importantly, ExD techniques have been applied beyond protein analyses, which is the focus of the current paper. This short introduction describes the application of ExD to small and medium-sized molecules and reviews important applications to natural products, biomedical compounds, synthetic molecules, crude oils, and environmental toxins.
Collapse
Affiliation(s)
- Yulin Qi
- Institute of Bioanalytical Chemistry, Saarland University, 66123 Saarbrücken, Germany.
| | | |
Collapse
|
7
|
Wei J, O'Connor PB. Extensive fragmentation of pheophytin-a by infrared multiphoton dissociation tandem mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:2411-2418. [PMID: 26563711 DOI: 10.1002/rcm.7391] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Revised: 09/04/2015] [Accepted: 09/07/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE In a previous tandem mass spectrometry (MS/MS) study on chlorophyll-a, infrared multiphoton dissociation (IRMPD) was demonstrated as a more effective fragmentation method than collision-induced dissociation (CID) and electron-induced dissociation (EID), where odd-electron product ions were observed ubiquitously in CID and IRMPD. To further understand the role of the macrocycle and the central Mg atom in the MS/MS process, the fragmentation behaviour of pheophytin-a, the Mg-free chlorophyll-a, was investigated. METHODS CID, IRMPD, and EID were applied to the singly protonated pheophytin-a using an ultra-high-resolution Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The result is compared with the MS/MS study of chlorophyll-a. RESULTS For pheophytin-a, some different fragmentation patterns from chlorophyll-a were obtained by all three MS/MS methods, but IRMPD still appears the most efficient method of generating product ions. The detection of odd-electron fragments in the CID and IRMPD spectra of protonated pheophytin-a suggests that the macrocyclic structure effectively stabilizes radicals, and these radical ions seem to have a relatively higher abundance in the presence of the central Mg atom. CONCLUSIONS The strong absorption in the infrared region of pheophytin-a and secondary free radical rearrangement are proposed to explain the extensive frgmentation in IRMPD spectra. In addition, a comparison of the IRMPD spectra of chlorophyll-a and pheophytin-a shows that the macrocycle in the absence of the Mg atom is much more fragile.
Collapse
Affiliation(s)
- Juan Wei
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | - Peter B O'Connor
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| |
Collapse
|
8
|
Voinov VG, Bennett SE, Barofsky DF. Electron-induced dissociation of peptides in a triple quadrupole mass spectrometer retrofitted with an electromagnetostatic cell. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:752-61. [PMID: 25652934 PMCID: PMC4446792 DOI: 10.1007/s13361-014-1074-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 12/18/2014] [Accepted: 12/19/2014] [Indexed: 05/02/2023]
Abstract
Dissociation of peptides induced by interaction with (free) electrons (electron-induced dissociation, EID) at electron energies ranging from near 0 to >30 eV was carried out using a radio-frequency-free electromagnetostatic (EMS) cell retrofitted into a triple quadrupole mass spectrometer. The product-ion mass spectra exhibited EID originating from electronically excited even-electron precursor ions, reduced radical cations formed by capture of low-energy electrons, and oxidized radical cations produced by interaction with high-energy electrons. The spectra demonstrate, within the limits of the triple quadrupole's resolving power, that high-energy EID product-ion spectra produced with an EMS cell exhibit essentially the same qualitative structural information, i.e., amino acid side-chain (SC) losses and backbone cleavages, as observed in high-energy EID spectra produced with a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. The levels of fragmentation efficiency evident in the product-ion spectra recorded in this study, as was the case for those recorded in earlier studies with FT ICR mass spectrometers, is currently at the margin of analytical utility. Given that this shortcoming can be remedied, EMS cells incorporated into QqQ or QqTOF mass spectrometers could make tandem high-energy EID mass spectrometry more widely accessible for analysis of peptides, small singly charged molecules, pharmaceuticals, and clinical samples.
Collapse
Affiliation(s)
- Valery G Voinov
- Department of Chemistry, Oregon State University, Corvallis, OR, 97330, USA,
| | | | | |
Collapse
|
9
|
Cera L, Schalley CA. Supramolecular reactivity in the gas phase: investigating the intrinsic properties of non-covalent complexes. Chem Soc Rev 2014; 43:1800-12. [PMID: 24435245 DOI: 10.1039/c3cs60360a] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The high vacuum inside a mass spectrometer offers unique conditions to broaden our view on the reactivity of supramolecules. Because dynamic exchange processes between complexes are efficiently suppressed, the intrinsic and intramolecular reactivity of the complexes of interest is observed. Besides this, the significantly higher strength of non-covalent interactions in the absence of competing solvent allows processes to occur that are unable to compete in solution. The present review highlights a series of examples illustrating different aspects of supramolecular gas-phase reactivity ranging from the dissociation and formation of covalent bonds in non-covalent complexes through the reactivity in the restricted inner phase of container molecules and step-by-step mechanistic studies of organocatalytic reaction cycles to cage contraction reactions, processes induced by electron capture, and finally dynamic molecular motion within non-covalent complexes as unravelled by hydrogen-deuterium exchange processes performed in the gas phase.
Collapse
Affiliation(s)
- Luca Cera
- Institut für Chemie und Biochemie, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany.
| | | |
Collapse
|
10
|
Yin Z, Wang X, Li W, He M, Hang W, Huang B. Thermal Diffusion Desorption for the Comprehensive Analysis of Organic Compounds. Anal Chem 2014; 86:6372-8. [DOI: 10.1021/ac500602t] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Zhibin Yin
- Department of Chemistry and the MOE Key Lab of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Xiaohua Wang
- Department of Chemistry and the MOE Key Lab of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Weifeng Li
- Department of Chemistry and the MOE Key Lab of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Miaohong He
- Department of Chemistry and the MOE Key Lab of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Wei Hang
- Department of Chemistry and the MOE Key Lab of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Benli Huang
- Department of Chemistry and the MOE Key Lab of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| |
Collapse
|
11
|
Wei J, Li H, Barrow MP, O'Connor PB. Structural characterization of chlorophyll-a by high resolution tandem mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:753-760. [PMID: 23504642 DOI: 10.1007/s13361-013-0577-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Revised: 12/20/2012] [Accepted: 12/31/2012] [Indexed: 06/01/2023]
Abstract
A high resolution Fourier transform ion cyclotron resonance (FTICR) mass spectrometer is used for characterizing the fragmentation of chlorophyll-a. Three tandem mass spectrometry (MS/MS) techniques, including electron-induced dissociation (EID), collisionally activated dissociation (CAD), and infrared mutiphoton dissociation (IRMPD) are applied to the singly protonated chlorophyll-a. Some previously unpublished fragments are identified unambiguously by utilizing high resolution and accurate mass value provided by the FTICR mass spectrometer. According to this research, the two long aliphatic side chains are shown to be the most labile parts, and favorable cleavage sites are proposed. Even though similar fragmentation patterns are generated by all three methods, there are much more abundant peaks in EID and IRMPD spectra. The similarities and differences are discussed in detail. Comparatively, cleavage leading to odd electron species and H(•) loss both seem more common in EID experiments. Extensive loss of small side groups (e.g., methyl and ethyl) next to the macrocyclic ring was observed. Coupling the high performance FTICR mass spectrometer with contemporary MS/MS techniques, especially IRMPD and EID, proved to be very promising for the structural characterization of chlorophyll, which is also suitable for the rapid and accurate structural investigation of other singly charged porphyrinic compounds.
Collapse
Affiliation(s)
- Juan Wei
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | | | | | | |
Collapse
|
12
|
Wills RH, Tosin M, O'Connor PB. Structural characterization of polyketides using high mass accuracy tandem mass spectrometry. Anal Chem 2012; 84:8863-70. [PMID: 22985101 DOI: 10.1021/ac3022778] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The tandem mass spectrometry techniques electron-induced dissociation (EID) and collision-activated dissociation (CAD) have been compared as tools for providing detailed structural information of polyketides. Polyketides are an important class of natural products that account for a significant proportion of the drugs currently in clinical use. Three polyketide natural products, namely erythromycin A, lasalocid A, and iso-lasalocid A, were subjected to both CAD and EID, and their fragment ions were assigned with sub-part-per-million accuracy. The number of fragment ions detected through EID was much greater than for CAD, leading to a greater amount of structural information obtained for each polyketide, albeit with a decreased signal-to-noise ratio. The effect of different bound cations on the fragment pattern of the isomers lasalocid A and iso-lasalocid A was studied, with CAD and EID performed on the [M + H](+), [M + Na](+), [M + Li](+), and [M + NH(4)](+) precursor ions. The lithiated species were found to produce the greatest degree of fragmentation and enabled detailed structural information on the isomers to be obtained. Multistage mass spectrometry (MS(3)) experiments, combining CAD and EID, could also be performed on the lithiated species, generating new fragment information which enables the two isomers to be distinguished. Combining CAD and EID for the structural characterization of polyketides will therefore be a useful tool for identifying and characterizing unknown polyketides and their biosynthetic intermediates.
Collapse
Affiliation(s)
- Rebecca H Wills
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | | | | |
Collapse
|
13
|
Kalli A, Grigorean G, Håkansson K. Electron induced dissociation of singly deprotonated peptides. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:2209-2221. [PMID: 21952776 DOI: 10.1007/s13361-011-0233-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2011] [Revised: 08/11/2011] [Accepted: 08/12/2011] [Indexed: 05/31/2023]
Abstract
Dissociation of singly charged species is more challenging compared with that of multiply charged precursor ions because singly charged ions are generally more stable. In collision activated dissociation (CAD), singly charged ions also gain less kinetic energy in a fixed electric field compared with multiply charged species. Furthermore, ion-electron and ion-ion reactions that frequently provide complementary and more extensive fragmentation compared with CAD typically require multiply charged precursor ions. Here, we investigate electron induced dissociation (EID) of singly deprotonated peptides and compare the EID fragmentation patterns with those observed in negative ion mode CAD. Fragmentation induced upon electron irradiation and collisional activation is not specific and results in the formation of a wide range of product ions, including b-, y-, a-, x-, c-, and z-type ions. Characteristic amino acid side chain losses are detected in both techniques. However, differences are also observed between EID and CAD spectra of the same species, including formation of odd-electron species not seen in CAD, in EID. Furthermore, EID frequently results in more extensive fragmentation compared with CAD. For modified peptides, EID resulted in retention of sulfonation and phosphorylation, allowing localization of the modification site. The observed differences are likely due to both vibrational and electronic excitation in EID, whereas only the former process occurs in CAD.
Collapse
Affiliation(s)
- Anastasia Kalli
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109-1055, USA
| | | | | |
Collapse
|