Peter J. Derrick

Determination of translational energy release distributions through analysis of metastable peaks

Abstract A method is described for the analysis of metastable peak shapes to obtain translational energy release distributions. The method takes account of instrumental factors such as collector and energy-defining (β) slit widths, Z-axial discrimination, field-defining shunts, lengths of field-free regions, and the parent peak shape. Results of other methods of analysis are compared with those of the new method.

Slow alkyl, alkene, and alkenyl loss from primary alkylamines: Isomerization of the low-energy molecular ions prior to fragmentation in the μsec timeframe

Abstract Isomerization of the molecular ion precedes alkyl radical elimination from many primary aliphatic amines. Rearrangement of the carbon skeleton is initiated by 1,5-hydrogen abstraction by the -NH 2 +· and converts primary-alkyl amines to sec - and tert -alkyl amines; fragmentation is then by α-cleavage of the rearranged molecular ions. Isomerization is also encountered for amines branched at the α-carbon atom. The elimination of propene from n -pentylamine and of a butenyl radical from neo -pentylamine is discussed. Remote (δ or e) cleavage does not contribute to the low-energy reactions.

Alkane loss from the molecular ions of alcohols, ketones, and amines in the μsec timeframe

Abstract Neutral alkane molecules are eliminated in the low-energy reactions of many low molecular weight secondary alcohols, ketones and sec-alkyl primary amines. The alkane molecule consists of one α-alkyl group plus a hydrogen atom from the first carbon of the ‘other’ α-alkyl (formally a simple 1,2-elimination). Alkane loss competes inefficiently with other intramolecular hydrogen abstraction reactions (e.g., the McLafferty rearrangement), and is only observed for compounds with relatively short alkyl groups. When an α-substituent is methyl exceptional behavior is sometimes encountered: alkane loss is not important for methyl ketones (except acetone), and methane loss from α-methyl amines occurs only for isopropylamine. Tertiary alcohols have not been observed to eliminate alkane molecules, and alkane loss does not occur for secondary and tertiary amines.

Mass spectroscopy at high mass

ZusammenfassungDie Definition „Hoher Massenbereich“ in der Massenspektroskopie gilt für Ionen oberhalb von m/z 10000. Es wird eine Übersicht über Ionisierungstechniken, Methoden der Massentrennung und der Ionendetektion gegeben. Ein allgemeingültiger Mechanismus der Bildung von Ionen in der Gasphase aus nicht flüchtigen, thermisch empfindlichen Verbindungen wird vorgestellt. Der Vorschlag beschreibt als gemeinsame Eigenschaft dieser Ionisierungstechniken die Ausbildung einer Ladung an der Grenzschicht zwischen kondensierter Phase und Vakuum bei anschließender feldinduzierter Verdampfung der Ionen.SummaryHigh mass in mass spectroscopy is defined as being the region above m/z 10000. Ionization techniques, methods of mass analysis and ion detection are reviewed. A general mechanism of formation of gaseous ions from nonvolatile, thermally labile compounds is put forward. The characteristics in common to all ionization techniques are, it is proposed, the setting-up of a charge at the condensed phase/vacuum interface, and the subsequent field evaporation of ions.

Plasma desorption mass spectra of the three-dimensionally non-molecular material [Cd(SC6H4CH3-4)2]∞: formation of cadmium-containing cluster ions

Plasma desorption mass spectra of the cadmium compound [Cd(SC6H4CH3-4)2]∞ have been obtained in both positive- and negative-ion modes. The positive-ion mass spectra in particular provide detailed structural information on this inorganic material. Samples have been loaded by electrospraying the solution in dimethylformamide and by the nitrocellulose-substrate technique. The positive-ion mass spectra exhibit peaks corresponding in mass to clusters of the general formula [Cdx(SC7H7)2x−1]+, up to x = 8.

A model of ion evaporation tested through field desorption experiments on glucose mixed with alkali metal salts

Abstract In field desorption (FD) mass spectra of mixtures of glucose and Li, Na, K, and Cs salts, with the latter present in equimolar parts, the relative intensities of Li-, Na-, K-, and Cs-containing ions of the same type are not equal and vary with total salt concentration. The patterns of peak intensities are explained on the basis of a model of ion evaporation in which the gaseous ions are ejected from the tips of microscopic protuberances (heights 1–2 nm) which develop on the surface of the sample. The action of the external electric field favours evaporation of ions containing smaller alkali metals because the larger “solvation” shells can be drawn into longer protuberances and the evaporating ions are smaller. This effect counters the tendency for ions containing larger alkali metals to be evaporated preferentially on account of weaker ion/molecule interactions.