Evaluation of the true effect of experimental parameters on the reduction / oxidation processes observed in fast-atom bombardment/liquid secondary spectrometry

Abstract

The peak intensities observed in the molecular ion regions of fast-atom bombardment/liquid secondary ion mass spectra contain contributions from the parent ion species, its one- and two-electron reduction/oxidation products, and chemical background signal due to beaminduced damage. There are several solution and instrumental parameters that can affect the distribution of peak intensities in the molecular ion region. In this study, the analyte concentration and primary beam density and energy were varied systematically to investigate their effects on the measured peak intensities. A computer algorithm, Simbroc (Simulated Background and Reduction/Oxidation Calculations), was designed to deconvolute the observed intensities into their individual components so that the true effects of experimental parameters on redox extent and background levels could be evaluated. The algorithm is based on a comprehensive seven-variable mathematical model for experimental data simulation. The results obtained using the algorithm after its validation indicate that the primary beam energy does not significantly affect redox extent or background levels. Changes in analyte concentration and primary beam density tend to play a more important role in the generation of redox products and beam-induced damage. The background level generally increases as the analyte concentration is lowered for the peptide systems used in this study. An increase in the primary beam density often leads to higher background levels, although the effect is less detectable for samples that have a low (less than 3%) background signal. The apparent two-electron reduction is generally lower at the higher concentrations; however, the "true" reduction occurring for pentaphenylalanine does not show a significant concentration effect.

Determination of flux from a saddle field fast-atom bombardment gun

“…The image consisted of a bright central region of fairly uniform intensity, surrounded by a diffuse ring of much lower intensity, as has been observed elsewhere [15]. At the short gun-target distance employed (-4 Emission Current (rnA) Visentini et al [26] observed similar saturation at high flux. The detailed reasons for this saturation are under study.…”

“…The beam-induced reduction of methylene blue has been studied extensively [14,[16][17][18][19][20][21][22][23][24][25][26]. For the purposes of this discussion, only the I-hydrogen atom reduction product will be considered, although 2-hydrogen atom reduction can also be extensive.…”

“…As background contributions increase (i.e., decreasing signal-to-background ratio at long t due to sample depletion [16,27]), the value of E[ will approach a flux-independent steady state. Visentini et al [26] have shown that these effects can be neglected only if the signal-to-background (SjB) ratio is at least 30:1.…”

Study by liquid secondary ion and electrospray mass spectrometry of synthesized and formed‐in‐source metallocorroles

“…Therefore, the formation of metallocorrole positive ions in‐source from divalent metal cations could involve the oxidation of the metal centre. Although atom/ion bombardment induced reductions are well known and are widespread reactions, atom/ion bombardment induced oxidation reactions are much less common 28–31. On the other hand, oxidation reactions in the metal capillary sprayers of mass spectrometers operating in the positive mode are an important step in the overall ionization process, being responsible for charge balance 32, 33…”