Electron Impact Conditions Research Articles

Mass spectroscopic studies of riboflavin and isotopically labelled lumiflavins

AbstractUnder electron impact conditions 3‐methylriboflavin is attacked at the ribityl side chain to generate 3‐methyl‐lumiflavin. This is verified by analysis of metastable fragmentations and comparison with model ions. Formation of 1,3‐dimethyl‐lumkhrome through migration of the methyl group from N(10) to position N(1) is positively excluded. A general fragmentation scheme for ionized 3‐methyl‐lumiflavin is developed based on exact mass measurements using various2H,13C and15N isotopically labelled derivatives. The predominating initial loss of CH3NCO exclusively involves the 3‐ and 4‐positions, for which an asynchronous mechanism is discussed.

Features of Si rearrangement in the structural analysis by mass spectrometry

Attention is drawn to the general nature of rearrangement processes which in silylated organic compounds by non-bonded interactions of the ionized Si centre with nucleophilic functional groups produce significant amounts of recombination products under electron impact conditions. Several typical examples involving different functional groups are shown to illustrate the appearance of the resulting characteristics.

The electron impact mass spectra of di- and trinitrofluoranthenes.

The fragmentation pathways of a series of 18 dinitrofluoranthenes (DNF) and four trinitrofluoranthenes have been studied under electron impact conditions. In general, multiple losses of NO2, NO and CO from the molecular ion were observed. Quinonoid ions were observed in the spectra of DNF containing conjugated nitro groups. In addition, some unique fragmentation pathways were detected in the ortho-substituted 1,2- and 2,3-DNF and in the peri-substituted 3,4-DNF.

Fragmentation of 2-thienylsilanes under electron impact

The electron impact (EI) mass spectra of 2-thienylsilanes have been studied. It has been found that species containing the SiS bond take part in fragmentation, indicating intramolecular interaction of the silicon and sulphur atoms under EI conditions. The mass spectra are characterized by silicon-containing ions and also by intense peaks of silicon-free ions. Based on the mass spectrometric data, the following sequence of SiR relative strengths in thienylsilanes is found: SiCH 3 < SiH < Si(2-thienyl) < SiCl.

Use of tandem mass spectrometry (MS-MS) for aldosterone assay at the nanogram level in complex biological mixtures

Aldosterone in biological samples was measured comparatively by two methods: radioimmunoassay (RIA) and tandem mass spectrometry. The last method is described in this paper. Aldosterone was derivatized as butane boronate cyclic ester. This derivative gives an intense molecular ion under 70-eV electron impact conditions. This ion exhibits an abundant metastable decomposition in the second field free region by loss of formic acid, which can be used for the assay. A linear relationship was observed between the ionic current and the amount of aldosterone from 10 to 200 ng. A good correlation between this new method and the radioimmunological assay is observed. Aldosterone can be readily detected at the nanogram level.

S-S exchange of cysteine-containing peptides in different methods of mass spectrometric analysis

1. Mass spectra of five cysteine-containing peptides and their mixtures were obtained by mass spectrometry methods under the conditions of electron impact, chemical ionization, field desorption bombardment by accelerated electrons and extraction of ions from solution under atmospheric pressure. 2. It was found that under ESIAP conditions, the cysteine-containing peptides do not undergo the S-S exchange observed in their investigation by other ionization methods.

Capillary column isobutane chemical ionization mass spectrometry of mustard and related compounds

Capillary column isobutane chemical ionization was found to be an excellent method for the mass spectral characterization of mustard, other sulfur vesicants and related compounds. Interpretation of [M + H]+ and fragmentation ion information afforded by this technique enabled the identification of many previously unreported mustard impurities. The developed methodology was applied to the analysis of an Iran/Iraq soil sample suspected to have been contaminated with mustard. Mustard and 17 other mustard related impurities were identified and characterized in this sample under electron impact and isobutane chemical ionization conditions.

Mass spectrometric behaviour of pentachlorophenyl β-carbonylenolate phosphino nickel(II) complexes: An example of thermal generation of a nickel(III) species

The mass spectral behaviour of pentachlorophenyl β-carbonylenolate phosphino nickel(II) square planar complexes has been investigated under electron impact (EI) and field desorption (FD) conditions. The fragmentation has been interpreted on the basis of the B/E linked scans and mass-analysed ion kinetic energy (MIKE) techniques. The acetylacetonate diphenylphosphino complex was found to undergo a solid state reaction in the probe, which led to the generation in situ of a nickel(III) chloro complex. Careful control of instrumental conditions and computer-assisted EI measurements made it possible to characterize the addition products as [NiCl(C 6Cl 5)(AcAc)PPh 2Me] and to propose a mechanism for its solid state generation.

Identification of degradation products of 2-chloroethyl ethyl sulfide by gas chromatography-mass spectrometry

Gas chromatography-mass spectrometry under both electron impact and methane chemical ionization conditions has been used to detect impurities and degradation products present in the mustard simulant 2-chloroethyl ethyl sulfide, with a detection limit of 0.05 area percent. After one and two years of storage at ambient temperatures, the primary degradation product was 1,4-dithiane formed from the degradation of dimeric sulfonium ions. Oxidation and hydrolysis products were not detected.

Identification of degradation products of 2-chloroethyl ethyl sulfide by gas chromatography—mass spectrometry

Gas chromatography-mass spectrometry under both electron impact and methane chemical ionization conditions has been used to detect impurities and degradation products present in the mustard simulant 2-chloroethyl ethyl sulfide, with a detection limit of 0.05 area percent. After one and two years of storage at ambient temperatures, the primary degradation product was 1,4-dithiane formed from the degradation of dimeric sulfonium ions. Oxidation and hydrolysis products were not detected.

Direct coupling of open-tubular liquid chromatography with mass spectrometry.

The design and performance of a probe that allows direct liquid introduction of the total effluent of an open-tubular liquid chromatography (OTLC) column into a mass spectrometer are described. No modification of the mass spectrometer source is required, and the probe is introduced through the direct insertion probe inlet. Because flow rates are less than 0.1 ..mu..L/min, this system can be used under both conventional electron impact and chemical ionization mass spectrometric conditions. The probe has been used with glass OTLC columns (0.5-mm o.d., 16-..mu..m i.d.) and fused silica columns (0.35-mm o.d., and 5- or 10-..mu..m i.d.). Tapering and heating the end of the column allow for the detection of compounds of low volatility while maintaining good peak shape and minimizing band broadening. A separation of five pesticides is shown, for which detection limits in the low picogram levels in the full-scan mode were obtained by using methane negative chemical ionization (MNCI). The analysis of two isomeric triazine herbicides by using OTLC with electron impact ionization mass spectrometry is also shown.

Effect of the structure of the π-ligand on the mechanism of ion-molecule reactions in the (η6-ARENE) chromium tricarbonyl-ammonia system

Correlations were found between the structure of the π-ligand in (η6-arene)chromium tricarbonyls and their behavior under conditions of electron impact and chemical ionization with NH3 as the reagent gas. It was shown that, in principle, information may be obtained on the structure of organometallic ions in the gas phase from the data for ion-molecule reactions with ammonia.

On the origin of the peaks of some substituted ions in the mass spectra of lecithins

AbstractPreliminary results concerning the origin of the peaks of some substituted ions in the mass spectra of lecithins, obtained under electron impact and chemical ionization conditions, are reported.

Analysis of O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) by capillary column gas chromatography-mass spectrometry.

A sample of stored O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX), known to contain many impurities, was studied by combined capillary column gas chromatography-mass spectrometry under both electron impact and chemical ionization conditions. More than twenty sample components, many of which were previously unreported, were identified and characterized based on their mass spectral data. Ammonia chemical ionization was particularly useful since this technique provided molecular ion information for all the VX impurities.

Intrinsic acidity and basicity of neutral and ionic species of some polyether‐ester compounds as shown by mass spectrometry

AbstractThe mass spectrometric behaviour of benzo‐[o]‐1,4,7,10,13‐pentaoxacycloheptadecane‐14,17‐dione (1), 3,6,9,12,15‐pentaoxabicyclo[15.3.1]heneicosa‐1(21),17,19‐triene‐2,16‐dione (2) and 1,15‐dioxo‐2,5,8,11,14‐pentaoxa[15](1,4)benzenophane (3) has been studied in detail with the aid of linked scans, mass‐analysed ion kinetic energy spectra, collisionally activated decomposition experiments, exact mass measurements and different ionization techniques (electron impact, positive and negative ion chemical ionization, charge exchange, electron attachment). The very low abundance of molecular ions and the presence of abundant [M + H]+ and [M – H]+ ions under electron impact conditions indicate the presence of acidic and basic sites in the molecular ions and neutral molecules, respectively.

Electron impact induced fragmentations of 2‐chlorovinyl methyl sulphides

AbstractA series of 2‐chlorovinyl methyl sulphides, CH3SCR1CR2Cl (R1, R2 = H, Me, Et, t‐Bu, Ph; R1 = H, R2 = CH3) has been analysed under electron impact conditions. The most significant common fragmentations involve primary loss of Cl˙ and methyl radicals. Analysis of the phenyl‐substituted derivative suggests that loss of CH3˙ is a lower activation energy process than loss of Cl˙. The characteristic loss of CH3SCl from the same derivative has been examined with respect to the structure of the resulting fragment by means of suitable model compounds.

Heteryladamantanes. Communication 5. Synthesis of 6-(1-adamantyl)-3-cyanopyridin-2(1H)-selenone and related selenophenopyridines

1. Reaction of the sodium salt of 3-(1-adamantyl)-1-hydroxyprop-1-en-3-one with cyanoselenoacetamide led to the first synthesis of 6-(1-adamantyl)-3-cyanopyridine-2(1H)-selenone. 2. 2-Seleno substituted 6-(1-adamantyl)-3-cyanopyridines have been obtained by alkylation of pyridineselenone with RCH2HA1. Cyclization in the presence of base gives 2-substituted 6-(1-adamanty1)-3-aminoselenopheno[2,3-b]pyridines. 3. Under electron impact conditions 2-mercapto and 2-seleno substituted 6-(1-adamantyl)-3-cyanopyridines undergo cyclization to the corresponding substituted thieno- and selenophenopyridines. The sulfur-containing compounds do not show an ion peak corresponding to separation of the adamantyl and pyridyl rings, whereas such a process does occur in the case of the selenium analogs.

Mass spectrometric studies on cyclo‐ and poly‐phosphazenes: 3—Polymerization of tris(o‐diphenylenedioxy)cyclotriphosphazene, [NP(O2C6H4)]3

AbstractThe polymerization reaction of tris(o‐phenylenedioxy)cyclotriphosphazene, [NP(O2C6H4)]3, occurs in the ion chamber of a mass spectrometer under high‐sample vapour pressure conditions, leading to the formation of tetrameric, pentameric and hexameric species. There is evidence that, under electron impact conditions, the phosphonitrilic ring of [NP(O2C6H4)]3 breaks down, giving rise to a linear phosphazene radical cation, from which the polymerization reaction takes place by means of successive additions of neutral NP(O2C6H4) units. A comparison is made between this reaction and mass spectrometrically induced polymerizations of hexachloro‐ and hexa(phenoxy)‐cyclophosphazenes, previously reported.

Mass spectrometry of o?, m?, and p-carboranes(12)

Under electron impact conditions, dehydrogenation is the main fragmentation process of isomeric carboranes(12). The progress of this process enhances with the increase of the energy of ionizing electrons and the temperature of the ionization chamber.

Investigations on antipyrine metabolism V. Differentiation of two isomeric hydroxyantipyrine glucuronides by field desorption and fast atom bombardment mass spectrometry.

The glucuronide conjugates of the two isomeric antipyrine phase I metabolites of antipyrine in man, 4-hydroxyantipyrine and 3-hydroxymethylantipyrine have been analysed by field desorption and fast atom bombardment mass spectrometry. These isomers could be clearly distinguished on the basis of their fragmentation behaviour which was found to correlate with that observed under pyrolysis electron impact conditions.