MASS SPECTROMETRIC FRAGMENTATION OF TRIMETHYLSILYL AND RELATED ALKYLSILYL DERIVATIVES

This review describes the mass spectral fragmentation of trimethylsilyl (TMS) and related alkylsilyl derivatives used for preparing samples for analysis, mainly by combined gas chromatography and mass spectrometry (GC/MS). The review is divided into three sections. The first section is concerned with the TMS derivatives themselves and describes fragmentation of derivatized alcohols, thiols, amines, ketones, carboxylic acids and bifunctional compounds such as hydroxy- and amino-acids, halo acids and hydroxy ethers. More complex compounds such as glycerides, sphingolipids, carbohydrates, organic phosphates, phosphonates, steroids, vitamin D, cannabinoids, and prostaglandins are discussed next. The second section describes intermolecular reactions of siliconium ions such as the TMS cation and the third section discusses other alkylsilyl derivatives. Among these latter compounds are di- and trialkyl-silyl derivatives, various substituted-alkyldimethylsilyl derivatives such as the tert-butyldimethylsilyl ethers, cyclic silyl derivatives, alkoxysilyl derivatives, and 3-pyridylmethyldimethylsilyl esters used for double bond location in fatty acid spectra. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 0000:1-107, 2019.

Evaluation of automatically generated substructure identification rules from tandem mass spectra

Substructure identification rules for phenothiazine and barbiturate substructures were generated by using a new version of the Method for Analyzing Patterns in Spectra (MAPS) software. This software uses tandem mass spectra and known substructure content of reference compounds to provide "feature-combination" rules. A feature-combination is a series of tandem mass spectral features which are completely unique to compounds containing a specified substructure. The current reference databases contain over 11,000 daughter spectra of 100 compounds acquired at two different collision gas pressures (i.e., single- and multiple-collision conditions). The results of rule evaluation procedures are presented and include a comparison of the spectral features developed in rule generation to those identified in documented fragmentation pathways of the indicated substructure. Two potential sources of error due to spectral feature and substructure "cross-correlation" were identified. If errors occur, they can be detected by calculating cross-correlation coefficients and edited from the rules. A beneficial cross-correlation involving feature-combinations was also discovered. The rules obtained by using single- and multiple-collision data were further evaluated by applying them to tandem mass spectra of 20 test compounds (compounds not in the reference database). The results of these evaluations give a good indication of the utility of the rules for use in an automated structure elucidation system for tandem mass spectrometry data.

Anion mass spectrometry of barbiturates

Recent trends towards increasing abuse of the barbiturates has led to a proposal to legally restrict some of them. The implementation of the resulting legislation might require specific identification of the barbiturates. Such identification is not readily available from electron impact mass spectra and, even when these are supplemented with chemical ionization data, barbiturates differing only in isomeric sidechains are not completely characterized. In this study the anion mass spectra of 30 barbiturates, including all of those commonly available, are presented. The spectra are simple; ions arising from hydrogen atom and sidechain elimination from the initially formed [M]- ion are diagnostic of the barbiturate. For all but two of the barbiturates (butalbital and idobutal) relative peak intensities will discriminate between barbiturates differing only in isomeric sidechains.

Gas chromatographic analysis of dialkylbarbituric acids

A variety of procedures for the derivatization of barbituric acids for gas-liquid chromatography (GLC) are described and a convenient procedure for n-alkylation of barbiturates is reported. The gas chromatographic behavior of derivatives(methyl, ethyl, propyl, butyl, pentyl and hexyl) is discussed on the basis of the retention index. For the identification and quatitation of 23 barbiturates in biological fluids, use of the propyl derivatives allows a clear gas chromatogram to be obtained by using only one stationary phase. Alkylation with n-alkylating reagents gives only the N,N'-derivative, as confirmed by nuclear magnetic resonance (NMR) and infrared spectroscopy and gas chromatography-mass spectrometry (GC-MS). The fragmentation pattern by electron-impact mass spectrometry is discussed. Alkylation with branched alkylating reagents gives up to three peaks, the major peak being the N,N'-derivative; the other peaks identified by NMR and GC, correspond to the isomeric N,O-derivatives.