Ammonia Chemical Ionization Spectra Research Articles

Electron impact and ammonia chemical ionization mass spectra of n‐azabicyclo[m.2.0]alkan‐(n + 1)‐ones (m = 3–6, n = 6–9)

AbstractElectron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low‐resolution, high‐resolution, B/E and B2/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7‐azabicyclo[4.2.0]octan‐8‐one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C3H3O]+, [CkH2k‐2N]+ (k = 5–8) and [C3H6N]+. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]+, [M + 1 + NH3]+˙ and [2 M + 1]+˙.

Distinction between 17‐epimeric hydroxy steroids of the 3,17‐dioxygenated androstane series by chemical ionization

AbstractThe distinction between 17‐epimeric 3,17‐dioxygenated hydroxyandrostanes has been made by comparison of both their methane or ammonia positive and OH− negative chemical ionization (CI) mass spectra. In the methane or ammonia positive CI, the 17α‐configuration in the eight stereoisomeric 5ξ‐androstane‐3ξ,17ξ‐diols can be determined by the relative abundances of the ion [MH2 H2O]+. In the ammonia CI spectra, the ion [M+NH4H2O]+ possesses only a low abundance, but a comparison of the relative rates of the loss of water v. the loss of ammonia from [M.NH4]+ in the second field‐free region allows a clear distinction to be made between the 17α‐ and 17β‐series. In the OH− negative CI mass spectra, the 5ξ‐androstane‐3‐one‐17ξ‐ols produce an intense ion [MHH2O]− in the 17α‐series only.

Mass spectrometry of isomeric fatty acid hydroperoxides by chemical ionization via direct exposure probe

AbstractIntact isomeric methyl 9‐ and 13‐hydroperoxy linoleates are analyzed by chemical ionization (CI) mass spectrometry using a direct exposure probe. Both isobutane and ammonia CI spectra were obtained. With isobutane CI, ions are observed for protonated fragments that are indicative of an acid catalysis mechanism similar to that observed in solution, whereas ammonia CI yields primarily adduct ions. The collisionally activated decomposition daughters of the high mass ions can be used to identify the position of the hydroperoxy group in the isomers studied.

Recognition of functional groups by chemical ionization mass spectrometry

A means of recognition of functional groups in organic molecules using chemical ionization mass spectrometry is described. Mass spectra of 34 C27-steroids using methane, isobutane and ammonia as reagent gases are recorded and correlations with structure proposed. Ammonia chemical ionization spectra are most instructive, generally yielding abundant ions of four types: an ammonium adduct [M+ NH4]+, an ammonia displacement ion [M + NH3 - X]+, a protonated molecular ion [M + H]+ and an elimination ion [M - X]+. Both the [M + H]+ and [M - X]+ ions appear to derive from the ammonium adduct [M + NH4]+, and the ion [M + NH3 - X]+ derives by a nucleophilic displacement of an elimination fragment X by neutral ammonia. Steroid ketones and olefins give predominantly [M + NH4]+ and [M + H]+ ions, whereas alcohols and esters give a three-component pattern of [M + NH4]+, [M + NH3 - X]+ and [M - X]+ ions. Spectra derived using methane or isobutane as reagent gas contain three major ion types: the protonated molecular ion [M + H]+, the hydride abstraction ion [M - H]+ and the elimination ion [M - X]+. Steroid ketones give the [M + H]+ion predominantly; the olefins give both [M + H]+ and [M - X]+ ions. Steroid alcohols give [M + H]+, [M - X]− ions. Recognition by these means of functionality in nonsteroid compounds appears also to be possible.

Electron impact and chemical ionization mass spectrometry of steroidal spirolactones.

Electron impact and chemical ionization mass spectra are reported for several steroidal spirolactones and their TMS ethers. The electron impact spectra were characterized generally by low abundance molecular ions and large numbers of fragment ions. Methane chemical ionization spectra exhibited high intensity [M+H]+ and/or [M+H-H2O]+ or [M+H-TMSOH]+ ions with few other fragment ions. Ammonia chemical ionization spectra had intense [M+H]+ and/or [M+NH4]+ ions with a few fragment ions generally formed by loss of H2O or TMSOH from these parent ions. Ammonia chemical ionization gave intense parent ions even for polyhydroxy compounds and their TMS ethers in contrast to methane chemical ionization. The results of this study suggest that a combination of electron impact with ammonia chemical ionization mass spectrometry would offer the best techniques for detection and identification of these compounds in biological fluids.

Effects of bifunctional interactions in the chemical ionization mass spectrometry of carboxylic acids and methyl esters

AbstractThe methane chemical ionization mass spectra of dodecan‐1, 10‐dioic acid and the methyl ester show enhanced water and methanol elimination relative to monofunctional analogs. Elimination of acetic acid from 1,10‐diacetoxydecane, however, was reduced relative to 1‐acetoxydecane. This appears to be the result of bifunctional interactions. The steric requirement of this interaction is shown in an homologous series of dicarboxyl compounds. The change in interfunctional separation is shown to affect the proton and ammonium ion affinities in the ammonia chemical ionization spectra of the dicarboxyl compounds in a manner explained in terms of proton and ammonium ion complex formation. The observation is extended to various other functional groups.