Selective reagents in chemical ionization mass spectrometry: trimethylsilyl adduct ions

Abstract

Ternary mixtures of methane, tetramethylsllane, and smaller amounts of Lewis bases, B, like water, acetone, or dimethyl ether contain adduct Ions, (CH3)3SI-B+, as the major chemical Ionization (Cl) reactant Ions. These adduct Ions react by displacement reactions If the sample binds more strongly to the trimethylsilyl Ion than does the Lewis base, B, In the reagent gas mixture. The Cl spectra obtained with these reagent Ions frequently contain more adduct Ions and less fragmentation than the Cl spectra obtained with the trlmethylsllyl Ion from tetramethylsllane. The water adduct Ions undergo both proton transfer and displacement reactions, from which one can estimate that the proton affinity of trimethylsllanol Is 197 ± 2 kcal/mol (824 ± 8 kJ/mol) and that D[(CH3)3SI+-OH2] = 43 ±2 kcal/mol (180 ± 8 kJ/mol). The

Methane high-pressure collisional activation mass spectrometry of aromatic hydrocarbons

“…Much of the research in CIMS has been toward the development of low-energy reagent ions which give very simple mass spectra (3)(4)(5)(6). These spectra are useful for the qualitative and quantitative analysis of mixtures and for the determination of the molecular weight of the sample compound (7,8).…”

The proton affinity of triethylsilanol obtained by proton transfer equilibrium measurements using a high pressure mass spectrometer

“…[7] (C2H5)3SiOH2+ + C8HI0 = (C2H5)3SiOH + C 8 H l l + The calculated equilibrium constant at a given temperature is independent of both ion source pressure (2-4 Torr) and ratio of neutral molecules (varied by a factor of five). The standard enthalpy and standard entropy changes for the three equilibria are obtained from the van't Hoff plots of Fig.…”

“…Naphthalene production is sufficiently small compared with the rate of proton exchange (reaction [7]) that the equilibrium is not disturbed. [7] (C2H5)3SiOH2+ + C8HI0 = (C2H5)3SiOH + C 8 H l l + The calculated equilibrium constant at a given temperature is independent of both ion source pressure (2-4 Torr) and ratio of neutral molecules (varied by a factor of five).…”

Sodium ion attachment reactions in an ion trap mass spectrometer

“…In general, an addition complex is formed with a correlated representative mass peak in the resulting mass spectrum. Trimethylsilyl adduct cations have been used as selective reagents5,, 6 and have proved to be efficient in, for example, the detection of oxygenated compounds in gasoline blends7 or the detection of explosives 8…”