Letter: Characteristics of Photoelectrons Emitted in Matrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Experiments

Gorshkov, Mikhail V.; Frankevich, Vladimir; Zenobi, Renato

doi:10.1255/ejms.474

Eur J Mass Spectrom (Chichester)

2002

DOI: 10.1255/ejms.474

|View full text |Cite

Letter: Characteristics of Photoelectrons Emitted in Matrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Experiments

Mikhail V. Gorshkov

Vladimir Frankevich

Renato Zenobi

Abstract: We show a simple method to study the characteristics of electrons emitted from the metal target in matrix-assisted laser desorption/ionization (MALDI) experiments. The method is based on measurements of SF 6 ion appearance curves by introducing SF 6 as a buffer gas into the vacuum chamber during laser desorption. We obtained the energy distribution of emitted electrons, as well as information on their origin and on ion formation mechanisms in MALDI experiments.

Help me understand this report

Search citation statements

Order By: Relevance

Paper Sections

Select...

Citation Types

Supporting

Mentioning

Contrasting

Year Published

2002

2008

Publication Types

Select...

Article7

Relationship

Self Cite3

Independent4

Authors

Journals

Cited by 34 publications

(42 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The origin and the amount of free electrons in MALDI has not been comprehensively investigated before and many questions were still open [22]. Recently, studies of the origin of the free electrons in MALDI from our laboratory [23,24] have shown that free electrons are largely formed by photoelectric emission from a metal/ dielectric-substance interface, not by photoionization of matrix [21]. Our studies also showed that the yield of electrons strongly depends on the thickness of the matrix layer.…”

mentioning

confidence: 69%

Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry

Zhang¹,

Frankevich²,

Knochenmuss³

et al. 2003

J. Am. Soc. Mass Spectrom.

Self Cite

View full text Add to dashboard Cite

The mechanisms of the reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) are studied. In MALDI mass spectra, ions cationized by copper mostly contain Cu(I) even if Cu(II) salts are added to the sample. It was found that Cu(II) was reduced to Cu(I) by gas-phase charge exchange with matrix molecules, which is a thermodynamically favorable process. Under some conditions, large amounts of free electrons are present in the plume. Cu(II) can be even more efficiently reduced to Cu(I) by free electron capture in the gas phase. The matrices studied in this work are nicotinic acid, dithranol, and 2,5-dihydroxybenzoic acid. ϩ ) were observed in the analysis of proteins [11,17,19,20] and polar synthetic polymers, e.g., polyethylene glycols (PEG) [12], whereas in the analysis of apolar synthetic polymers, e.g., polystyrene (PS), the reduction of divalent metal ions was dominant [13][14][15][16]18].In this work, we present a detailed study of the reduction of divalent copper used as a cationization agent in MALDI. Different explanations of this reduction in the gas phase have been given, namely electron capture [21] and charge exchange with matrix [22]. The origin and the amount of free electrons in MALDI has not been comprehensively investigated before and many questions were still open [22]. Recently, studies of the origin of the free electrons in MALDI from our laboratory [23,24] have shown that free electrons are largely formed by photoelectric emission from a metal/ dielectric-substance interface, not by photoionization of matrix [21]. Our studies also showed that the yield of electrons strongly depends on the thickness of the matrix layer. In the case of nonmetallic surfaces, few electrons are produced.According to these results, we are able to investigate the roles of free electrons and matrices as possible reducing agents in MALDI separately. Blocking the electron source by using a nonmetallic sample carrier or a metallic target covered with an insulating layer provides the possibility to examine the effect of the gasphase charge transfer between divalent metal ions and the matrices. For investigation of the effect of the free electron capture, experiments have to be done in the absence of matrix by using direct laser desorption/ ionization (LDI) of the sample.Under continuous extraction conditions, for example on a time-of-flight (TOF) mass spectrometer, free electrons as the most mobile species can either be extracted very quickly (in the negative ion mode) or pushed back towards the target (in the positive ion mode) and thus have less overlap with the plume, i.e., electrons will be less available for capture by positively charged species. On the other hand, delayed extraction allows time for secondary ion-molecule reactions to occur, e.g., the charge transfer reaction between neutral matrix molecules and copper ions. In order to investigate the influence of the high extraction field on the free electron capture and the charge exchange reaction, we have compared the results ...

show abstract

mentioning

confidence: 69%

Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry

Zhang¹,

Frankevich²,

Knochenmuss³

et al. 2003

J. Am. Soc. Mass Spectrom.

Self Cite

View full text Add to dashboard Cite

show abstract

“…23 The presence of matrix molecules or analytes placed on a metal target enhances electron emission via band bending and the associated reduction in work function. 22,23 Thus, electron transfer from the sample target would be essential for understanding the analyte reduction in LDI.In desorption/ionization on porous silicon, termed DIOS, 26 analytes are deposited on a silicon chip, which is prepared by electrochemical anodization or chemical etching of crystalline silicon, for LDI without the addition of a chemical matrix. The DIOS mass spectra are thus free of cluster ions of the matrix, facilitating identification of the ions of small analyte molecules.…”

mentioning

confidence: 99%

“…8,9 A line of studies has indicated that free electrons are formed by photoelectric emission from the metal/dielectric-substance interface. [22][23][24][25] The metal sample target is not the photoelectron source, because the work function of metals is greater than the photon energy. 23 The presence of matrix molecules or analytes placed on a metal target enhances electron emission via band bending and the associated reduction in work function.…”

mentioning

confidence: 99%

“…[22][23][24][25] The metal sample target is not the photoelectron source, because the work function of metals is greater than the photon energy. 23 The presence of matrix molecules or analytes placed on a metal target enhances electron emission via band bending and the associated reduction in work function. 22,23 Thus, electron transfer from the sample target would be essential for understanding the analyte reduction in LDI.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Oxidation of Ferrocene Derivatives in Desorption/Ionization on Porous Silicon

2005

View full text Add to dashboard Cite

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is currently an indispensable method for analyzing biomolecules and synthetic polymers. [1][2][3][4][5][6] While the mechanism of ionization is largely unknown, physical data on the ionization potentials and the gas-phase acidity or basicity have been accumulating, and the roles of the matrix-matrix, matrix-analyte and analyte-analyte reactions in both primary and secondary ionization events have been evaluated in some detail. [7][8][9][10][11][12][13][14][15][16] These studies have suggested the secondary ionmolecule reactions in the plume to be essential to understanding the process of ionization and the mass spectrum. 7,9,11 Some analytes are reduced by these reactions as follows: Copper(II) ions are reduced by laser desorption/ionization (LDI) with or without a chemical matrix. 16Flavin-containing compounds, such as riboflavin, riboflavin 5′-phosphate and flavin-adenine dinucleotide, are reduced in MALDI and fast atom bombardment (FAB) ionization, but not in electrospray ionization, as reported by Itoh et al., who also found that the reduction levels depend on the matrix molecule types. 17 In the case of nitrotyrosine, the NO2 moiety is partially converted into NH2, probably due to reduction after photo-induced dissociation by UV laser irradiation. 18,19 Similarly, the S-nitrosylated cysteine, Cys(SNO), in peptides is completely converted to cysteine, Cys(SH), in MALDI. 20,21 Different mechanisms, such as electron capture and charge exchange with the chemical matrix, have been proposed to account for the reductions in MALDI. 8,9 A line of studies has indicated that free electrons are formed by photoelectric emission from the metal/dielectric-substance interface. [22][23][24][25] The metal sample target is not the photoelectron source, because the work function of metals is greater than the photon energy. 23 The presence of matrix molecules or analytes placed on a metal target enhances electron emission via band bending and the associated reduction in work function. 22,23 Thus, electron transfer from the sample target would be essential for understanding the analyte reduction in LDI.In desorption/ionization on porous silicon, termed DIOS, 26 analytes are deposited on a silicon chip, which is prepared by electrochemical anodization or chemical etching of crystalline silicon, for LDI without the addition of a chemical matrix. The DIOS mass spectra are thus free of cluster ions of the matrix, facilitating identification of the ions of small analyte molecules. DIOS-MS has been applied to various kinds of compounds, such as peptides, natural products, small organic molecules and synthetic polymers. [26][27][28][29][30][31][32][33][34][35][36] The ionization efficiency of DIOS relies on a porous scaffold providing a sufficient surface area to retain analytes, and on the UV-absorptive property, which affords the transfer of laser energy to analytes. 26,27 In contrast to MALDI, chemical reactions in a plume composed of analytes and the sample ma...

show abstract

Sensitivity of redox reactions of dyes to variations of conditions created in mass spectrometric experiments

et al. 2008

View full text Add to dashboard Cite

Redox behaviour of four imidazophenazine dye derivatives under mass spectrometric conditions of matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization (LDI) from metal and graphite surface, electrospray, low temperature secondary ion mass spectrometry (LT SIMS) and fast atom bombardment (FAB) was studied and distinctions in the reduction-dependent spectral patterns were analyzed from the point of view of different quantities of protons and electrons available for reduction in different techniques. The reduction products [M + 2H](+*), [M + 3H](+) and M(-*), [M + H](-) were observed in the positive and negative ion modes, respectively, which permitted to suggest independent occurrence of reduction and protonation/deprotonation processes. LDI from graphite substrate was the only technique that allowed us to obtain abundant negative ions of all dye derivatives. The yield of field ionization (FI) or field desorption (FD) mechanism to ion formation under LDI from rough graphite surface has been addressed. The sensitivity of reduction of the dyes to variation of reduction-initiating agents confirms high redox activity of the dyes essential for their functioning in natural and artificial systems.

show abstract

scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.

Contact Info

customersupport@researchsolutions.com

10624 S. Eastern Ave., Ste. A-614

Henderson, NV 89052, USA

Blog Terms and Conditions API Terms Privacy Policy Contact Cookie Preferences Do Not Sell or Share My Personal Information

Made with 💙 for researchers

Part of the Research Solutions Family.

Letter: Characteristics of Photoelectrons Emitted in Matrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Experiments

Cited by 34 publications

References 7 publications

Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry

Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry

Oxidation of Ferrocene Derivatives in Desorption/Ionization on Porous Silicon

Sensitivity of redox reactions of dyes to variations of conditions created in mass spectrometric experiments

Contact Info

Product

Resources

About