Influence of ionization energy on charge-transfer ionization in matrix-assisted laser desorption/ionization mass spectrometry

Macha, Stephen F.; McCarley, Tracy D.; Limbach, Patrick A.

doi:10.1016/s0003-2670(99)00408-0

Cited by 60 publications

(67 citation statements)

References 13 publications

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“…The only adduct observed with the C-G discharge was an addition of 18 u, attributed to water. Both of these spectra match well with those published for typical APCI sources [22] and the commercial DART source [24].…”

Section: Ferrocene Determinationsupporting

confidence: 84%

“…This time-trace for m/z 186 is given in Figure 4a. It is important to note that while these sources typically ionize through proton transfer, ferrocene has a much lower ionization energy than gasphase basicity, resulting in mainly the molecular ion [22]. While the G-A discharge was running, there was a strong signal (ϳ70,000 counts) for the M ϩ of ferrocene.…”

Section: Ferrocene Determinationmentioning

confidence: 99%

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Characterization of direct-current atmospheric-pressure discharges useful for ambient desorption/ionization mass spectrometry

Shelley

Wiley

Chan

et al. 2009

J. Am. Soc. Mass Spectrom.

123

133

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Two relatively new ambient ionization sources, direct analysis in real time (DART) and the flowing atmospheric-pressure afterglow (FAPA), use direct current, atmospheric-pressure discharges to produce reagent ions for the direct ionization of a sample. Although at a first glance these two sources appear similar, a fundamental study reveals otherwise. Specifically, DART was found to operate with a corona-to-glow transition (C-G) discharge whereas the FAPA was found to operate with a glow-to-arc transition (G-A) discharge. The characteristics of both discharges were evaluated on the basis of four factors: reagent-ion production, response to a model analyte (ferrocene), infrared (IR) thermography of the gas used for desorption and ionization, and spatial emission characteristics. The G-A discharge produced a greater abundance and a wider variety of reagent ions than the C-G discharge. In addition, the discharges yielded different adducts and signal strengths for ferrocene. It was also found that the gas exiting the discharge chamber reached a maximum of 235°C and 55°C for the G-A and C-G discharges, respectively. Finally, spatially resolved emission maps of both discharges showed clear differences for N 2 ϩ and O(I). These findings demonstrate that the discharges used by FAPA and DART are fundamentally different and should have different optimal applications for ambient desorption/ionization mass spectrometry (ADI-MS). irect-current (DC) discharges have been widely used for elemental analyses since they were first introduced for alloy characterization [1]. When DC discharges were coupled with mass spectrometry, the result was a very sensitive and powerful tool for elemental [1] and molecular analyses [2,3]. Of the many electrical regimes of DC discharges, three forms have been found to have particular analytical merit: the arc, the glow, and the corona. Among these three types of discharges, the fundamental distinction is the operating current and voltage. The arc occurs at very high currents (hundreds of amperes) with a low voltage drop between electrodes (tens of volts). It also exhibits negative resistance; that is, the sustaining voltage drops as the current rises. The glow discharge (GD), which has conventionally been operated between 0.1 to 10 Torr, exists at much lower currents (tens of milliamperes) and a higher voltage drop (hundreds of volts). Lastly, the corona discharge operates with very low currents (a few microamperes) and a much higher voltage drop (several kilovolts).Corona discharges find their most common analytical application in atmospheric pressure chemical ionization (APCI) [4,5]. In conventional APCI, a corona discharge is formed by applying ϳ4 kV to a needle electrode in a selected atmosphere, to yield currents of ϳ5 A. After a series of reactions [5], reagent ions are produced that can then ionize a sample. Protonated water clusters are typically observed because of the presence of water vapor in the air. Such protonated clusters promote proton transfer ionization, resulting in mass spect...

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Section: Ferrocene Determinationsupporting

confidence: 84%

Section: Ferrocene Determinationmentioning

confidence: 99%

Characterization of direct-current atmospheric-pressure discharges useful for ambient desorption/ionization mass spectrometry

Shelley

Wiley

Chan

et al. 2009

J. Am. Soc. Mass Spectrom.

123

133

View full text Add to dashboard Cite

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“…1). 38,39 The observed isotopic pattern (M-2: 11; M-1: 3; M: 100; M+1: 29; M+2: 6) agrees well with the theoretical isotopic peak pattern (M-2: 13; M-1: 3; M: 100; M+1: 29; M+2: 5) of FcCH2CH2Fc + ion, indicating that a protonated molecule of 1,2-diferrocenylethane was not formed. N,NDimetylaminomethylferrocene (FcCH2NMe2, M = 243) has an amino group as well as a Fc center.…”

Section: Resultssupporting

confidence: 81%

“…42 Limbach and co-workers reported on the oxidation of ferrocene derivatives (ferrocene, 1,2-diferrocenylethane, and decamethylferrocene) in MALDI. 38,39 They proposed resonant two-photon ionization of the chemical matrix, followed by electron transfer from the analyte to the matrix molecule. Therefore, it was interesting to examine the oxidation of ferrocene derivatives by DIOS, since chemical matrices are not used in DIOS.…”

Section: Resultsmentioning

confidence: 99%

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Oxidation of Ferrocene Derivatives in Desorption/Ionization on Porous Silicon

2005

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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...

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Secondary ion-molecule reactions in matrix-assisted laser desorption/ionization

et al. 2000

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Ion-molecule charge- and proton-transfer reactions in the desorption plume are considered for the case of matrix-assisted laser desorption/ionization (MALDI) with ultraviolet laser excitation, and it is proposed that they are major determinants of the observed mass spectrum. Specific MALDI phenomena which are discussed include the dominance of singly charged ions and analyte-matrix or analyte-analyte signal suppression. Should any be formed, highly charged products can be reduced by reaction with neutral matrix, yet singly charged ions cannot generally be neutralized in the same manner. Ion suppression effects can also be explained by similar reactions, which in some cases involve interconversion of dissimilar ion types. The plume is proposed often to be more under thermodynamic rather than kinetic control owing to these secondary reactions. UV/MALDI mass spectra should therefore be largely predictable, given sufficient thermodynamic information, and appropriate experimental conditions of sufficient analyte and plume density. Copyright 2000 John Wiley & Sons, Ltd.

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Influence of ionization energy on charge-transfer ionization in matrix-assisted laser desorption/ionization mass spectrometry

Cited by 60 publications

References 13 publications

Characterization of direct-current atmospheric-pressure discharges useful for ambient desorption/ionization mass spectrometry

Characterization of direct-current atmospheric-pressure discharges useful for ambient desorption/ionization mass spectrometry

Oxidation of Ferrocene Derivatives in Desorption/Ionization on Porous Silicon

Secondary ion-molecule reactions in matrix-assisted laser desorption/ionization

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