Dominance of gas-phase basicities over solution basicities in the competition for protons in fast atom bombardment mass spectrometry

Sunner, Jan; Morales, Angelina; Kebarle, P.

doi:10.1021/ac00137a002

Cited by 69 publications

(32 citation statements)

References 22 publications

(39 reference statements)

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“…The possibility of simultaneous occurrence of the above two mechanisms in the framework of the ‘bubble chamber FAB model’ also addresses another question concerning FAB mechanisms, namely, whether gas‐phase or liquid‐phase processes are dominant in FAB 73–75. Gas‐phase interactions occur within the bubble, while mainly solution‐related processes are involved in the droplet evaporation mechanism, and the resulting spectrum emerges as a superposition of the two effects.…”

Section: Resultsmentioning

confidence: 99%

‘Bubble chamber model’ of fast atom bombardment induced processes

Kosevich

Shelkovsky

Boryak

et al. 2003

Rapid Comm Mass Spectrometry

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A hypothesis concerning FAB mechanisms, referred to as a 'bubble chamber FAB model', is proposed. This model can provide an answer to the long-standing question as to how fragile biomolecules and weakly bound clusters can survive under high-energy particle impact on liquids. The basis of this model is a simple estimation of saturated vapour pressure over the surface of liquids, which shows that all liquids ever tested by fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS) were in the superheated state under the experimental conditions applied. The result of the interaction of the energetic particles with superheated liquids is known to be qualitatively different from that with equilibrium liquids. It consists of initiation of local boiling, i.e., in formation of vapour bubbles along the track of the energetic particle. This phenomenon has been extensively studied in the framework of nuclear physics and provides the basis for construction of the well-known bubble chamber detectors. The possibility of occurrence of similar processes under FAB of superheated liquids substantiates a conceptual model of emission of secondary ions suggested by Vestal in 1983, which assumes formation of bubbles beneath the liquid surface, followed by their bursting accompanied by release of microdroplets and clusters as a necessary intermediate step for the creation of molecular ions. The main distinctive feature of the bubble chamber FAB model, proposed here, is that the bubbles are formed not in the space and time-restricted impact-excited zone, but in the nearby liquid as a 'normal' boiling event, which implies that the temperature both within the bubble and in the droplets emerging on its burst is practically the same as that of the bulk liquid sample. This concept can resolve the paradox of survival of intact biomolecules under FAB, since the part of the sample participating in the liquid-gas transition via the bubble mechanism has an ambient temperature which is not destructive for biomolecules. Another important feature of the model is that the timescale of bubble growth is no longer limited by the relaxation time of the excited zone ( approximately 10(-12) s), but rather resembles the timescale characteristic of common boiling, sufficient for multiple interactions of gas molecules and formation of clusters. Further, when the bubbles burst, microdroplets are released, which implies that FAB processes are similar to those in spraying techniques. Thus, two processes contribute to the ion production, namely, release of volatile solvent clusters from bubbles and of non-volatile solute from sputtered droplets. This view reconciles contradictory views on the dominance of either gas-phase or liquid-phase effects in FAB. Some other effects, such as suppression of all other ions by surface-active compounds, are consistent with the suggested model.

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Section: Resultsmentioning

confidence: 99%

‘Bubble chamber model’ of fast atom bombardment induced processes

Kosevich

Shelkovsky

Boryak

et al. 2003

Rapid Comm Mass Spectrometry

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“…Two esters (25 and 26) were synthesized from 24 by the usual acid-catalysed esterification with methanol and ethanol, respectively. 4-Aminobiphenyl (22) was obtained by reduction with activated iron powder of 4nitrobiphenyl (27), which was prepared by nitration of biphenyl. Decadeuterobiphenyl (19) was synthesized by silver bromide-catalysed coupling of pentadeuterophenyl magnesium bromide (Grignard reagent), which was obtained from pentadeuterobromobenzene.…”

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confidence: 99%

Structural and substituent effects on [M]^+.vs. [MH]⁺ formation in fast atom bombardment mass spectra of simple organic compounds

Nakata¹,

Tanaka²

1994

Org. Mass Spectrom.

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The peak intensity ratios of [ M ] +' YS. [ MH] + were measured in the fast atom bombardment (FAB) mass spectra of readily available test compounds with 3-nitrobenzyl alcohol as the matrix. For simple aromatic amines, the ratio increases as the ionization energy of the substrate decreases. CSubstituted benzophenones showed preferential formation of [MH]' ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenones have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett c r ' .Among 4-substituted biphenyls, both bromo and chloro substituents afforded abnormally high peak intensity ratios. The effects of the substituents in these compounds are discussed semi-quantitatively in terms of the Hammett correlation and the hard and soft acids and bases principle. The mechanism of ion formation in FAB and chemical ionization (CI) ion sources appeared to be different because some of the compounds studied showed an intense [MI+* peak with a relatively weak [MHI' peak in FAB spectra but exhibited a strong [ MH] + peak in ordinary CI spectra. a Unless stated otherwise, If and PA values were taken from Ref. 25 and pK, values of the conjugate acid of each amine from Ref. 26. 6 Diphenylamine 691 890" 1.1 Ref. 27. Estimated value from PA of 1 and 7.

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“…It is likely that several mechanisms contribute to the final desorption/ ionization yield. However, a previous study 8 has shown that gas-phase energetics dominate liquid-phase energetics in FAB-MS, suggesting that gas-phase proton affinities can serve as a useful guide to the protonating or deprotonating power of liquid matrices. Thus, glycerol, with a gas-phase proton affinity of 874 kJ/ mol, 9 is a more acidic matrix and a potential proton donor.…”

Section: Choice Of Matrix Componentsmentioning

confidence: 97%

Two‐phase Matrix‐assisted Laser Desorption/Ionization: Matrix Selection and Sample Pretreatment for Complex Anionic Analytes

Dale¹,

Knochenmuss²,

Zenobi³

1997

Rapid Commun. Mass Spectrom.

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Two-phase matrices, consisting of a binary mixture of solid particulates and a low vapour pressure liquid, are shown to be effective for the production of both positive-ion and negative-ion laser desorption/ionization mass spectra (LDI-MS). It was found that matrix selection can be guided by criteria developed previously for fast-atom bombardment mass spectrometry. Two-phase matrix-assisted (MA)LDI-MS of a variety of complex anionic analytes is presented. Sample pre-treatment using 'drop dialysis', or exposure to an acid-activated Nafion® cation-exchange membrane, substantially enhances the quality of negative-ion mass spectra. © 1997 by John Wiley & Sons, Ltd. Received 21 November 1996; Accepted 30 November 1996 Rapid Commun. Mass Spectrom. 11, 136-142 (1997 1-3 It is thought that laser radiation is absorbed by the solid particulates, causing desorption/ionization via rapid thermal evaporation of the liquid matrix. The binary mixtures have a number of advantages over their solid counterparts for matrixassisted laser desorption/ionization mass spectrometry (MALDI-MS). Most significantly, no co-crystallization of the matrix and analyte is required, and analyte diffusion through the liquid component can result in thorough mixing and homogenization of the sample. In addition, the liquid matrix is not required to have a UV chromophore. It has been shown previously 3 that, in two-phase matrices, the liquid provides protons and cations to the analyte, enhances analyte ion yields, improves resolution and increases signal stability and uniformity.The separation of the energy absorption (solid particulates) and solvent (liquid matrix) functions adds a new degree of flexibility which we use here to extend the application of two-phase MALDI to include the negative-ion mass spectrometry of involatile, intermediate-molecular-weight analytes. The choice of liquid matrices and solid particulates is discussed in this context. It is noted that liquid matrix selection can be guided by similar criteria to those previously determined in fast-atom bombardment mass spectrometry (FAB-MS). It is demonstrated that a two-phase matrix, consisting of diethanolamine and silicon particulates, can be used to obtain the mass spectra of complex organic phosphates and sulphonates, which are most readily analysed in the negative-ion mode. Sample pretreatment by dialysis and cation exchange is demonstrated to significantly improve mass spectral quality for these analytes. The use of both membrane drop dialysis and Nafion® cation exchange membranes is also discussed. EXPERIMENTALThe experiments were performed on a home-built 2 m linear time-of-flight mass spectrometer. Ions were extracted from the source region using a static 25 kV acceleration potential. Desorption was performed using the 337 nm output from a nitrogen laser (Laser Science Inc. VSL-337ND-T), incident at ca. 30° to the sample surface. Laser attenuation was achieved using glass slides and an adjustable iris. The laser spot size was estimated to be an ellipse of axes ca. 0.1 × 0.2 mm...

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Dominance of gas-phase basicities over solution basicities in the competition for protons in fast atom bombardment mass spectrometry

Cited by 69 publications

References 22 publications

‘Bubble chamber model’ of fast atom bombardment induced processes

‘Bubble chamber model’ of fast atom bombardment induced processes

Structural and substituent effects on [M]^+.vs. [MH]⁺ formation in fast atom bombardment mass spectra of simple organic compounds

Two‐phase Matrix‐assisted Laser Desorption/Ionization: Matrix Selection and Sample Pretreatment for Complex Anionic Analytes

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Dominance of gas-phase basicities over solution basicities in the competition for protons in fast atom bombardment mass spectrometry

Cited by 69 publications

References 22 publications

‘Bubble chamber model’ of fast atom bombardment induced processes

‘Bubble chamber model’ of fast atom bombardment induced processes

Structural and substituent effects on [M]+.vs. [MH]+ formation in fast atom bombardment mass spectra of simple organic compounds

Two‐phase Matrix‐assisted Laser Desorption/Ionization: Matrix Selection and Sample Pretreatment for Complex Anionic Analytes

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Structural and substituent effects on [M]^+.vs. [MH]⁺ formation in fast atom bombardment mass spectra of simple organic compounds