Paul Vouros

Some stereochemical factors in the formation of rearrangement ions in the mass spectra of trimethylsilyl derivatives of steroidal phosphates

Abstract The mass spectra of trimethylsilyl derivatives of organic phosphates exhibit characteristic rearrangement ions involving both trimethylsilyl and hydrogen migrations to the phosphate moiety. It is shown that in molecules of relatively rigid structure, such as steroids, the processes leading to the formation of the rearrangement ions are dependent on the positioning of the functional groups.

Ion-Molecule Reaction Products Found in the Mass Spectra of Trimethylsilyl Derivatives

Abstract Mass spectrometric studies of trimethylsilyl derivatives of glycerophosphates revealed the presence of several ions of mass greater than M+. It is suggested that these ions are formed by the reaction of abundant fragment ions containing positively charged silicon with neutral molecular species.

Some Aspects of Intra- and Inter-Molecular Reactions of Siliconium Ions in the Vapor Phase

Abstract Intramolecular rearrangement processes in the mass spectra of trimethylsilyl derivatives of hydroxy steroids are discussed in terms of the reaction of a siliconium center and a heteroatom. The reaction is shown to be stereospecific. The reactivity of siliconium cations also results in the occurrence of intermolecular reactions under electron impact ionization conditions. Tetramethylsilane is used as a precursor for the production of siliconium ions and examples of chemical ionization mass spectra employing this reagent are shown.

Ion detection in mass spectrometry. The dependence of ion-sensitive plate response on ion structure and composition

The response of various types of ion-sensitive plates as a function of ion structure and composition has been investigated. Several ions of similar nominal mass and equal energy covering a wide variation in structure have been studied. It has been found that the response of the emulsion is dependent on the structure and composition of the impinging ion. The selectivity of emulsion response to molecular ions of variant structure is discussed in terms of a mathematical model proposed by Honig. The experimental results suggest that monoatomic ions and ions generally containing a smaller number of atoms produce darker photographic images than ions of the same mass and energy, but of more polyatomic nature. Ions of similar structure produce images of equal relative intensity but a dependence on chemical composition is also apparent. The evaporated silver bromide plates exhibited a linear relationship of total peak area versus log relative exposure over a dynamic range of at least 100.

Ion Energy Effects in Photographic Detection in Organic Mass Spectrometry

Abstract The relative response of emulsion (Ilford Q2) and evaporated AgBr (Ionomet) plates to a polyatomic (C9H20 +) and a monoatomic (129Xe+) ion has been studied as a function of ion energy. Data from the former are readily interpreted qualitatively and semi-quantitatively. Previously reported fragmentation numbers of impacting ions are corrected. Evidence is suggested to relate fragmentation number to a thermodynamic quantity.