Electron Impact Conditions Research Articles

Competing oxygen transfers from nitro group to sulphur and allenic double bonds in allenyl o‐nitrophenyl sulphides on electron impact

AbstractInteresting oxygen transfers from the o‐nitro group to allenic carbons were observed in allenyl o‐nitrophenyl sulphides under electron impact conditions giving rise to abundant fragment ions at m/z 151, 138 and 136. However, a similar oxygen transfer to the sulphur leads to another intense ion at m/z 145. The proposed fragmentation pathways and the ion structures were established through high‐resolution data, collision‐activated dissociation mass‐analysed ion kinetic energy and B/E linked‐scan spectra.

The electron impact, chemical ionization and fast atom bombardment positive ion mass spectra of 1,2-bis(sulfonyl)methylhydrazines

A series of bis(sulfonyl)-1-methylhydrazines were analyzed by positive ion electron impact (EI), chemical ionization (CI) and fast atom bombardment (FAB) mass spectrometry. Since these compounds showed activity against the L1210 leukemia, an understanding of their mass spectral behavior is important should the structural characterization of metabolites be required. FAB proved to be the most useful technique, generally providing abundant protonated molecule ion peaks, in contrast to the weak peaks observed with CI (ammonia or isobutane) and the total absence of molecular ion peaks in the EI mass spectra. In addition, utilizing FAB eliminated the problem of thermal decomposition, which was very difficult to control under EI and CI experimental conditions. Fragments observed in FAB and CI mass spectra were consistent with protonation at the methyl-bearing nitrogen. One can locate the R1 and R2 moieties relative to the methyl-bearing nitrogen in FAB and CI by assigning that nitrogen as the site of protonation, with subsequent elimination of R2SO2H.

Unusual neutral and radical losses in 2′‐substituted N‐phenylanthranilic acids on electron impact

AbstractUnusual expulsions of [H2O + CO2] from the M+˙ of N‐(o‐carboxyphenyl)anthranilic acid, [H2O + CH2O] from the M+˙ of N‐(o‐methoxyphenyl)anthranilic acid and [H2O + ˙NO2] from the M+˙ of N‐(o‐nitrophenyl) anthranilic acid were observed under electron impact conditions. These processes are stepwise in the corresponding para‐substituted N‐phenylanthranilic acids. The proposed fragmentation pathways and their mechanisms are supported by B/E linked‐scan spectra, collision‐activated decomposition (CAD)–mass‐analysed ion kinetic energy (MIKE) spectra, high‐resolution data, deuterium labelling and chemical substitution.

Analysis of regioisomers of α-O- and α-N-substituted oxazolidines using tandem mass spectrometry with electron impact and ammonia chemical ionization

Fragmentations induced by collision-activated dissociation of α-O- and α-N-substituted oxazolidines are demonstrated under ammonia chemical ionization (CI) and electron impact (El) conditions. Discrimination of these regioisomers is achieved using either conventional EI mass spectra or daughter ion mass spectra of the protonated molecules under ammonia CI conditions.

Repeller-Induced dissociation of alkyl alcohols in thermospray mass spectrometry

Six alkyl alcohols were studied using thermospray mass spectrometry. Whereas the dominant ion in the spectrum up to a repeller potential of 120 V was [M+NH 4 ] + , above that potential [M+H] + and fragment ions appeared. The fragments observed were largely due to hydrogen release from alkyl ions ([C n H 2n+1 ] + −H 2 →[C n H 2n−1 ] + ) and loss of water or some other stable molecule from the same species. The results are compared with those from ionization of the same alcohols under electron impact and photoionization conditions and with results obtained for methanol under thermospray conditions

Electron impact mass spectra of novel tetrahydroimidazo [4, 5, l-jk] [1, 4]benzodiazepin-2(1H)-one derivatives

Mass spectral fragmentations of nine benzodiazepin derivatives were examined by exact mass measurement and by metastable ion analysis. Under electron impact conditions, all compounds give rise to a molecular ion and ions of m/z 160, 159, 147, 131, 104, 77, 56, 41, and 39. Key fragmentation pathways are discussed for these ions.

Electron impact-induced fragmentation of some aminonitropyridines

The fragmentation behaviour of 18 vicinally substituted aminonitropyridines was studied under electron impact conditions. Tbe decomposition patterns were found to be strongly dependent on the position of substituents. The formation of the aza analogue of carbazole seems to affect considerably the fragmentation of 3-nitro-2-phenylaminopyridine.

Mass spectra of N,N,N′,N′-tetramethyl-1,4-phenylenediamine using nitrogen laser and electron impact ionization

Mass spectra are reported for N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPD). Both electron impact ionization (19 eV and 50 eV electrons) and nitogen laser photoionization (λ = 337 nm) were utilized, and the respective spectra are discussed and compared. In addition, a particularly curious ionization behavior observed under conditions of concurrent laser illumination and electron impact is described; it is proposed that these observations may reflect a cooperative process of electron impact ionization of photoexcited TMPD.

Neutralization‐Reionization Mass Spectrometry and Matrix Isolation of Some 9‐Silaanthracenes

AbstractNeutralization‐reionization mass spectrometry of silaanthracene radical cations, which are generated from the 9,10‐dihydro‐9‐silaanthracenes 1, 3, 8 and 11 under electron‐impact conditions, indicates that silaanthracenes are stable molecues in the gas phase. Flash pyrolysis of the starting compounds mentioned above also yields the silaanthracenes 2, 4, and 10, which may be isolated in an argon matrix at 15 K and exhibit characteristic UV spectra.

Electron impact and chemical ionization mass spectra of norbornane/ene di‐exo and di‐endo‐fused 1,3‐oxazin‐2(1H)‐ones and 1,3‐oxazine‐2(1H)‐thiones

AbstractMass spectral fragmentations of four norbornane/ene di‐exo‐ and di‐endo‐fused 1,3‐oxazin‐2(1H)‐ones and four 1,3‐oxazine‐2(1H)‐thiones were examined by means of metastable ion analysis, the collision‐induced dissociation technique and exact mass measurement. Under electron impact (EI) conditions all the saturated compounds gave rise to complicated fragmentations, including several rearrangements. For the unsaturated compounds, a retro‐Diels‐Alder (RDA) process was the most favoured fragmentation pathway, which took place with hydrogen rearrangement to yield RDA + H fragments. The EI mass spectra did not permit isomeric differentiation. Under chemical ionization conditions, stereochemical effects were more perceptible, but isomeric differentiation was still difficult.

Mass spectrometric investigation of para‐substituted benzenesulphinamide derivatives

AbstractUnder electron impact conditions the mass spectrometric behaviour of secondary and tertiary para‐substituted benzenesulphinamide derivatives has been studied. The fragmentation modes of these compounds, including a characteristic H2O loss from the molecular ions of N‐benzylamides, deduced with the aid of high‐resolution techniques, are described.

Analysis of beech wood samples, its milled wood lignin and polysaccharide fractions by curie-point and platinum filament pyrolysis-mass spectrometry

Beech wood samples (stem, root and biodegraded wood) as well as beech milled wood lignin, beech polysaccharide fractions (holocellulose, xylan and technical xylan) and microcrystalline cellulose were analysed by pyrolysis-mass spectrometry (Py-MS), i.e. Curie-point pyrolysis low voltage electron impact (EI) MS, as well as by in-ion source platinum filament pyrolysis MS under both ammonia chemical ionisation (CI) and low voltage EI conditions. The mass spectra reveal the presence of monomeric, submonomeric as well as di- and oligomeric pyrolysis products from polysaccharides and/or lignin. The difference in pyrolytic behavior of polysaccharides in the complex wood matrix and of the purified polysaccharides may find its cause in chemical and physical interactions between polysaccharides and lignins in the wood, or may be due to the presence of considerable amounts of inorganic cations in the sample. The pyrolytic behavior of lignin is not significantly influenced by the presence of inorganic cations. The holocellulose and xylan data also exhibit chlorinated lignin marker compounds, which point to the presence of partly chlorinated lignin in the sample. This is probably an artefact due to the isolation procedure of these fractions, which involves treatment with sodium hypochlorite solution. The CI data of the technical xylan fraction indicate the presence of di- and oligomeric pentoses, hexoses and pentose/hexose sugars. These are probably formed during the isolation procedure (which involves extraction of wood chips at 170°C) by partial depolymerisation of the polysaccharide moiety.

Formation of β‐carbolines from 1‐[(1′ ‐carboxy‐2′‐indol‐3′‐yl‐ethyl)amino]‐1‐deoxy‐D‐fructose under electron impact conditions

AbstractInterest in β‐carbolines has recently increased owing to their detection in human tissue and in some food products; one of the possible sources of their formation in food is the Amadori rearrangement product (ARP) of tryptophan with glucose, l‐[(1′‐carboxy‐2′‐indol‐3′‐ylethyl)amino] ‐1‐deoxy‐D‐fructose. Based on the intermediates identified in the high‐resolution electron impact spectrum of the tryptophan Amadori product and by B/E and B2/E linked‐scan experiments, a mechanism is proposed for their formation under electron impact conditions. The proposed mechanism is an intramolecular nucleophilic substitution reaction of the dehydrated tryptophan ARP, leading to the formation of 3‐substituted β‐carbolines; this mechanism might shed some light on the origin of their abundant formation in food.

Gas chromatographic and mass spectrometric determination of some resin and fatty acids in pulpmill effluents as their pentafluorobenzyl ester derivatives

A sensitive gas chromatographic method for the determination of resin and fatty acids commonly found in pulpmill effluents is presented. The acids are extracted from effluent samples at pH 8 by methyl tert.-butyl ether and converted into their respective pentafluorobenzyl ester derivatives. After silica gel column cleanup, sample extracts are analyzed by gas chromatography with an electron-capture detector using a 30-m DB-17 column. Mass spectral data of these esters obtained under electron impact and electron capture negative ion chemical ionization conditions are also described. The abundant and characteristic (M — 181) − ions are used for the identification and quantitation of resin and fatty acids using a selected ion monitoring technique. Using an effluent with a low blank, spiked recovery of a mixture of 15 acids at 1000-, 100- and 10-μg/1 levels is quantitative. Based on a 25-ml sample and a concentration factor of 10, the method detection limit is 1 μg/1 for all acids. Application of this procedure to some Canadian pulpmill samples is also presented.

Extensive substituent scrambling in substituted diphenylacetylenes on electron impact

AbstractExtensive randomization of the substituents is found in mono‐ and disubstituted diphenylacetylenes under electron impact conditions. The study of diphenylacetylenes with a variety of substituents indicates that the electron‐withdrawing groups favour the substituent scrambling, AH the substituted diphenylacetylenes give an ion at m/z 176, having a common ion‐structure, arising as a result of the expulsion of a hydrogen radical and the substituent in monosubstituted diphenylacetylenes and the expulsion of both the substituents in disubstituted diphenylacetylenes. A ring‐expanded structure is postulated for this common fragment.

Ruminal organic acid analysis by gas chromatography/mass spectrometry

Rumen fluid was analyzed by the gas chromatography/mass spectrometry (GC/MS) technique in order to identify the organic acids contained. The gas chromatogram obtained showed more than 200 peaks, and 60 organic acids were identified from their mass spectra obtained under electron impact conditions from the relative chromatographic peaks. Keto acids, polycarboxylic acids, hydroxy acids, aromatic acids, and saturated and unsaturated fatty acids were present, which were subdivided into three main groups: (i) short- and long-chain fatty acids; (ii) polyfunctional organic acids such as intermediate metabolic products; (iii) phenolic acids mainly from lignin and tannin degradation. It was concluded that GC/MS is a very specific and sensitive technique to detect the presence of fermentation products in biological fluids and that it could allow for the simpler and cheaper GC technique to be used for routine quantitative analyses of the identified compounds. Research on ruminal fermentation of feedstuffs is mainly based on measurements of pH, volatile fatty acids concentration, and turnover of markers. A more analytical approach is limited by difficult laboratory procedures regarding the identification and quantitation of the different biochemical pathways. We have recently used mass spectrometry/mass spectrometry (MS/MS) techniques to analyze the gas produced during the fermentation in the rumen (Bonsembiante et al., 1987a,b), and we have also adapted the MS/MS (McLafferty, 1983) and the gas chromatography/mass spectrometry (GC/MS) (McFadden, 1973) techniques to cope with the mixture analysis in order to study the chemical changes of ensiled grass (Bonsembiante et al., 1985; Daolio et al., 1986). The present work extends the method to analyze the nonvolatile organic acid profile of rumen fluid and to obtain the mass spectra of each component of the mixture. This basic research is a preliminary but essential step in order to carry out a complete compound screening and to perform routine quantitative analyses with a less sophisticated technique such as gas chromatography.

Identification of mustard related compounds in aqueous samples by gas chromatography/mass spectrometry

Abstract : Thiodiglycol and a number of other compounds were detected during gas chromatographic analysis of aqueous samples obtained from near the site of the former DRES mustard hydrolysate vaults. Hexane extracts of the aqueous samples were analysed by capillary column gas chromatography-mass spectrometry (GC-MS) under both electron impact and chemical ionization conditions. Interpretation of the MS and complementary capillary column GC-fourier transform infrared data led to the characterization and identification of many compounds, including ether/ thioether macrocycles and vinyl alcohol compounds, not previously associated with mustard decomposition. Keywords: Gas chromatography, Mass spectrometry, Chemical ionization, Ammonia, Isobutane, Chemical agent detection, Military chemical agents, Mustard, Canada.

Ortho effects in organic molecules on electron impact: 18—Novel hydrogen transfer from the methoxy group to acetylenic carbon in 2‐methoxyphenylacetylene and 2‐methoxydiphenylacetylenes

AbstractThe transfer of a hydrogen from the ortho methoxy group to the acetylenic carbon in 2‐methoxyphenylacetylene under electron impact conditions affords the rearranged molecular ion corresponding to 2H‐1‐benzopyran. Similar processes leading to cyclic products are also noticed in 2‐methoxydiphenylacetylenes. The ion structures and the mechanism of fragmentations are established through high‐resolution data, collision‐induced decomposition, mass‐analysed ion kinetic energy spectra, B/E linked scan spectra, D‐labelling and chemical substitution.

Gas phase reactivity of cation radicals and protonated species from isomeric C4H8S thioethers

AbstractFour isomeric thioethers, 2,3‐dimethylthiirane (1), 2‐methylthietane (2), tetrahydrothiophene (3), and allyl methyl thioether (4), have been subjected to mass spectrometric analysis in the gas phase, under electron impact (El) and chemical ionization (CI) conditions. The metastable molecular ions M+′ generated from 1‐4 under EI (70 eV) conditions give distinct patterns of unimolecular fragmentation, thus indicating that isomer interconversion reactions are slower than dissociation (a possible exception, to some extent, is the case of [M2]+′ and [M2]+′). The change of the relative intensities of some prominent peaks with increasing ion lifetime (decomposition within the ion source, the first, and the second field‐free regions of the mass spectrometer) is pointed out. Metastable [MH]+ ions, generated from 1‐4 in chemical ionization experiments with CH4, all eliminate H2 and H2S, although in different relative proportions. In addition to these processes protonated 4 also undergoes loss of C2H4 and C3H6, likely from a C‐protonated structure.

The mass spectra of some vicinally substituted nitropyridines

AbstractThe fragmentation behaviour of 22 vicinally substituted nitropyridines has been studied under electron impact conditions. The decomposition patterns were found to be strongly affected by interaction of the substituent with the nitro group and the ring nitrogen. AH fragmentation sequences depend to a great extent on the position of the substituent in the ring.