Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane with aliphatic alcohols

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.

Chemical ionization of substituted naphthalenes using tetrahydrofuran as a reagent in gas chromatography with ion trap mass spectrometry

The ion/molecule reactions of nine monosubstituted naphthalene compounds in chemical ionization mass spectrometry (CI-MS) were studied using tetrahydrofuran (THF) as CI reagent. Proton affinity factors, substituent effects and the preferred site of adduct ion attachment were examined. Good correlation was observed between proton affinity and the formation of [M](+*) and [M+H](+) ions. The influence of substituents on protonation and site-specific adduct [M+13](+) and [M+41](+) ion formation is also observed, with the cyano substituent showing the most stable [M+41](+) ion. Collision-activated dissociation experiments were used to characterize the variety of adducts formed under CI conditions, and provided insight into product ion structures and mechanisms of dissociation and condensation during CI-MS/MS.

Trimethylsilyl group migration in the mass spectra of trimethylsilyl ethers of cholesterol oxidation products. product ion characterization by linked-scan tandem mass spectrometry

Loss of the A ring in the electron-impact mass spectra of the trimethylsilyl (TMS) derivatives of several cholesterol oxidation products is accompanied by intramolecular migration of the 3-O-TMS group to the charge-retaining portion of the molecule. Linked-scan techniques (B/E and B(2)/E) were used to establish the fragmentation processes leading to the formation of the rearrangement ion. The TMS group appears to migrate to heteroatomic sites in the 5-; 6-, or 7-positions of the B ring. This structural assignment is supported by isotopic labeling studies and collision-induced dissociation of the resulting product ion.

Methylene substitution reactions in a quadrupole ion trap selectivity of ethylene, ethylene oxide, and dimethyl ether reactive ions

To elucidate the selectivity of methylene substitution reactions of monosubstituted and disubstituted oxyaromatic compounds in a low pressure quadrupole ion trap environment, the relative abundances of covalently bound and loosely bound adducts formed by ion/molecule reactions with ethylene (ET), ethylene oxide (ETOX), and dimethyl ether (DME) were compared. Adduct ions of all three reagent gases were formed in both a conventional ion source and a quadrupole ion trap and characterized by collisionally activated dissociation. For DME and ET, the covalently bound adducts formed at (M + 45)(+) and (M + 41)(+), respectively, are direct precursors to the methylene substitution product ions at (M + 13)(+). ETOX and ET do not demonstrate the same functional group selectivity for methylene substitution as previously observed for DME. This is attributed to differences in reaction exothermicities and competing reactions.

Radiative stabilization of trimethylsilyl adduct ions

Ketones and phenol react with trimethylsilyl ions to form adduct ions by radiatively or collisionally stabilized addition reactions, in contrast to aliphatic alcohols and ethers, which react with trimethylsilyl ions to form adduct ions by a rapid two-step process. Secondorder rate constants for the addition of trimethylsilyl ions to acetone were independent of pressure from 3×10(-7) to 50×10(-7) tort at room temperature; consequently, the adduct ions, [M+73](+), are formed primarily by radiatively stabilized addition in these ion cyclotron resonance experiments.