Mass Spectrometric Fragmentation of Trimethylsilyl and Related Alkylsilyl Derivatives

Abstract

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

Mass spectral fragmentation analyses of isotopically labelled hydroxy steroids using gas chromatography/electron ionization low‐resolution mass spectrometry: A practical approach

“…28 In contrast to an earlier described method for 18 oxygen exchange, while the acid catalysis method showed a strong dependence of exchange rates on the temperature and steric environment of the carbonyl group. Using acid-catalyzed labelling for 4-ene-3-ones such as testosterone, for example, a reaction time of 72 h was needed until the desired equilibrium was achieved, while the exchange procedure described herein only required less than 2 h. To obtain 18 O-labelled hydroxy groups, the labelled oxo steroids were reduced with NaBH 4 (Figure 1). Generally, these losses are considered to be rather unspecific and an explanation of their exact formation and their origin is rarely given.…”

“…Prior to GC/MS analyses, residues were derivatized with 90 μL 18 O-oxo groups (Figure 1). This fast and targeted method has also successfully been used in our group for other compounds such as benzophenone derivatives.…”

“…[1][2][3] Until the 1980s the fragmentation behavior of mostly underivatized steroids was the subject of extensive and systematic investigation [4][5][6] but has not been the main focus of research since. 18 O-labelling is not usually used for steroid research anymore but for other fields, for example metabolomics or peptide mass spectrometry. 7,8 In times of MS-library searches for compound identification stable isotopic labelling seems to be old fashioned and laborious.…”

“…Fragment ions explained by losses of TMS groups (e.g., loss of trimethylsilanol (TMSOH) [M -90] •+ ) as well as specific fragment ions derived from the steroidal A-, B-or D-ring are described in the literature. 12,[14][15][16][17][18] However, many questions concerning the mass spectra of TMS-derivatized steroids still remain unsolved and need to be addressed.…”

“…Thus, the aim of this paper is to contribute possible explanations for allegedly "unspecific" as well as more specific fragment ions in GC/MS for different steroid subclasses. Starting from isotopic labelling techniques for steroids established in the 1960s and 1970s, 6,[19][20][21][22][23] more viable and faster approaches for the introduction of deuterium and 18 O were developed and optimized in the presented work and their suitability shown for mass spectral fragmentation analysis. (8.4) were previously synthesized in our group.…”