Fast atom bombardment mass spectrometric study of some unsaturated aryl C-glycosides

Fast atom bombardment (FAB), FAB mass-analysed ion kinetic energy (FAB MIKE) and collision-activated dissociation (FAB CAD-MIKE) mass spectra were obtained for two series of unsaturated anomeric aryl C-glycosides. These tandem mass spectrometric techniques allowed the differentiation of the anomers by analysing either the [M + H]⁺ ion or the [M + met]⁺ ion (met=Li, Na).     

Electron impact and chemical ionization mass spectra of some unsaturated anomeric C-glycosides

Electron impact mass spectra at 70 eV electron energy and chemical ionization mass spectra with ammonia as the reagent gas are reported for certain unsaturated C-glycosides. Comparisons are made between the mass spectra of anomeric pairs of these glycosides.     

Fast atom bombardment mass spectrometric study of alkali metal cationized unsaturated C-glycosides

Fast atom bombardment mass spectrometry of alkali metal cationized unsaturated C-glycosides is a useful method for the determination of the molecular masses of these compounds. The mass-analyzed ion kinetic energy and collision-activated dissociation mass-analyzed ion kinetic energy spectra of the pairs of anomers are distinguishable and are characteristic of each anomer.     

Negative ion mass spectra of some classes of metal carbonyl halides

The negative-ion mass spectra at 70 eV of the compounds Re(CO)₅X (X = Cl, Br, I), Mn(CO)₅X (Br, I), Re₂(CO)₈X₂ (X = Cl, Br, I), Mn₂(CO)₈Br₂ and Rh₂(CO)₄X₂ (X = Cl, Br, I) are reported. The negative molecular ions are absent and the current is mainly transported by fragments due to the loss of carbonyl groups. In the spectra of the bimetallic compounds a rather high intensity is displayed by ionic species containing the two halide substituents. The variations in the ionic abundances are related to the change of the metal-CO bond strength, while the nature of X seems to play a minor role.     

Negative ion field desorption mass spectra of some inorganic and organic compounds

Field desorption of negative ions can be achieved below the threshold of field electron emission. To this end a mixture of the sample with polyethylene oxide and water was applied to smooth wire cathodes. The mass spectra of some inorganic and organic compounds are reported. Anionization by [CI]^? ion attachment is demonstrated with the examples of 20-hydroxycholesterol and sucrose.     

Negative ion mass spectra of dicarboxylic acids

The negative ion mass spectra of dicarboxylic acids show [M]^?˙ and prominent [M – H]^?ions. These ions can therefore be used to determine the molecular weight of dicarboxylic acids which do not give positive molecular ions. The [C₂H₃]^? ion is a base peak in the spectra of maleic and fumaric acids. Isomeric phthalic acids are readily differentiated.     

Negative ion mass spectra of chlorine-containing molecules

The negative ion mass spectra of chlorine-containing molecules have been measured using a double focusing mass spectrometer with a photographic plate detector. The formulae of the negative ions not previously assigned using an electron multiplier detector have now been assigned.     

Negative ion mass spectra of highly fluorinated compounds

The negative ion mass spectra of highly fluorinated molecules with varying functionality are discussed. Attempts to obtain negative molecular ions where no positive molecular ion was observed met with little success. An interesting structural correlation for fluorinated ethers was developed based upon the observation of the abundant perfluoro alkoxide anions, CF₃O^? and CF₃(CF₂)₂O^?, in the negative ion mass spectrum.     

Odd-electron molecular ion and loss of toluene in fast atom bombardment mass spectra of some carotenoids

Positive-ion fast atom bombardment (FAB) and B/E linked scan FAB mass spectra of seven carotenoids are reported. In all cases the M ^+· ions are observed, and the [M + H]⁺ ions are absent in the hydrocarbons and weak in the oxygenated compounds. The usefulness of B/E linked scan FAB mass spectra to distinguish isomers and to attribute the loss of toluene from the M ^+· to an ionic fragmentation and not to a thermal process is discussed.     

Negative ion mass spectrometry—I: The spectra of some stabilised alkylidenetriphenyl-phosphoranes

The 70 eV negative ion mass spectra of a series of phosphoranes exhibit significant peaks for ions resulting from skeletal rearrangements. The primary fragmentation reactions of the molecular anions, which involve reduction of the phosphorus from the penta- to the ter-valent state, have been rationalised in terms of the relative stabilities of the products formed. The processes occurring are in some cases analogous to and in other cases complementary to, those previously observed in the positive ion spectra of similar compounds.     

Fast atom bombardment and secondary ion mass spectra of thiamine hydrochloride

The ratio of the fragment ions at m/z 122 and m/z 123 in the positive ion fast atom bombardment or secondary ion mass spectra of thiamine hydrochloride varies with sample preparation and experimental conditions. For all mass spectra that contained significant abundances of matrix (S) ions [S + H]⁺, the fragment at m/z 123 is the more abundant of the two ions. If [S + H]⁺ ions are not observed in the mass spectrum under the conditions selected, the ion at m/z 122 is more abundant. This correlation suggests that hydrogen transfer to the fragment ion occurs in the gas phase, with the composition of the ion-solvent cluster ions in the selvedge region being the key factor. The ratio of the fragment ions at m/z 123 and m/z 122 is thus an indicator of the extent of protonation in the selvedge, the region immediately above the solvent surface created by primary particle bombardment.     

Negative ion mass spectra of various fluorine containing molecules

Negative ion mass spectra are reported for the compounds (CF₃CO)₂O, (C₂F₅CO)₂O, (C₃F₇CO)₂O, C₃F₇C(F)(CF₃)₂, n-C₆F₁₄, CF₃COCL, (CF₃)₂CO, BF₃, N₂F₄ and SiF₄.     

Fast atom bombardment mass spectra of some alkylammonium 4-toluenesulfonate salts

The fast atom bombardment positive ion mass spectra of low molecular weight alkylammonium 4-toluenesulfonate salts are dominated by cluster ions of the type [(AB)_nA]⁺ or [(AB)_nH]⁺, where A is a cation, B an anion, n an integer from 0 to 4. With one exception the base peak is the cation A⁺.     

Negative and positive mass spectra of some substituted trinitromethanes

The negative and positive ion mass spectra of a series of substituted trinitroalkanes (nitroform, tetranitro methane, methyl, fluoro, chloro, bromo and iodo-trinitro methane) have been measured with an Aatlas CH-4 Mass Spectrometer, under varying electron energies from 70 over the total range at which ions are produced. The modes of decomposition of the compounds are presented. A few metastable transitions are observable in the negative ion spectra, but only at high electron energies (ion pair region) and are very low in intensity. the negative and positive ion clastograms of these polynitro compounds showed little parent-daughter ion correlation. Finally, the negative ions formed appear to contain excess amounts of kinetic energy even at low electron energies; as a retult there is a great deal of overlap in the various mechanisms for the formation of negative ions.     

Negative and positive secondary ion mass spectra of organic acids

Organic compounds can be ionized by sputtering the solid sample. The resulting negative and positive secondary ions provide mass spectra which characterize both the molecular weights and the structures of the compounds. Ionization occurs either by direct ejection of charged species from the solid into vacuum or by electron or proton transfer. The sputtered secondary ions dissociate unimolecularly to give fragment ions. These reactions are identical to those which occur when the secondary ions are independently generated by chemical ionization, selected by mass and dissociated in a high energy gas phase collision. The negative ion SIMS spectra show molecular ions (M^?.) or (M-H)^? ions as the dominant high mass species together with fragments due to decarboxylation, dehydration and losses of other simple molecules. Stronger acids show larger (M-H)^?/M^?.abundance ratios. The positive ion spectra are complementary and also useful in characterizing molecular structures. Attachment of cations to organic molecules (cationization) occurs much more readily than anion attachment and this makes negative SIMS spectra simpler than these positive ion counterparts.