bluuebunny/crossref_metadata_2025 huggingface dataset:
Collisionally induced dissociative ionization of neutral products from ion fragmentations. 2—Collision gas effects and related phenomena
Authors: Clair Roberta , Holmes John L. , Mommers Alexander A. , Burgers Peter C.
Published: May 2005

The ion retardation method (whereby an ion beam is prevented from entering a collision gas cell by means of a voltage applied thereto) for permitting the examination of the neutral products of unimolecular ion fragmentations has been extended to include observations of neutral products generated by collisions before the gas cell and their related phenomenology. Observations obtained using an ion beam deflection electrode, an alternative method of preventing the ion beam from entering the collision cell, are also reported. When low collision gas pressures are employed (<2×10−7 Torr He), this latter method provides collisionally induced dissociative ionization (CIDI) mass spectra of unimolecularly generated neutral fragmentation products, free of complications arising from events induced by collisions occurring outside the collision cell. The CIDI mass spectra of CH3˙, C2H4, CH3ĊO, CH3OH and C2H6 generated from positive ion precursors and CH3˙, CH3O˙ and C6H5NO2 generated by electron loss from negative ions are described.
Fragmentation and rearrangement reactions in certain 1,2,3‐triaryl‐2‐propen‐1‐ones following electron impact and chemical ionization
Authors: Madhusudanan K. P. , Mittal Shubhra , Durani S. , Kapil R. S.
Published: May 2005

The electron impact (EI) and chemical ionization (CI) mass spectra of certain 1,2,3‐triaryl‐2‐propen‐1‐ones (TAPs) have been studied in detail with the help of exact mass measurements, deuterium labelling and metastable data. TheE‐ andZ‐isomeric pairs do not show any difference in their behaviour under EI or CH4CI conditions. EI‐induced rearangement reactions in the TAPs include aryl migration to carbonium ion centres. A study of the metastable transitions reveals aryl group interchange in the molecular ions prior to fragmentation. Under EI conditions loss of arene involves either C(2) or C(3) aryl groups while under CI conditions the C(1) aryl is lost as a neutral arene molecule. Mechanisms for the different fragmentation modes are given.
Chemical ionization mass spectrometry using a glow discharge ion source combined with a nebulizer sampling system
Authors: Matsumoto Kozo , Kojima Hisanoa , Yasuda Kazuhiro , Tsuge Shin
Published: May 2005

A glow discharge chemical ionization (CI) source equipped with a pneumatic nebulizer for sample introduction has been constructed. A comparative study of the discharge CI and conventional CI by electron impact from a hot filament is made for various polar compounds using oxygen‐containing reagents such as water and methanol. The potential utility of the discharge ion source to liquid chromatography/mass spectrometry is also discussed.
Stereospecific adduct ion formation in the chemical ionization mass spectra of E‐ and Z‐1,2,3‐triaryl‐2‐propen‐1‐ones
Authors: Madhusudanan K. P. , Mittal Shubhra , Durani Susheel , Kapil R. S.
Published: May 2005

Stereospecific adduct ion formation has been observed in the chemical ionization mass spectra (positive and negative) of certain E‐ and Z‐1,2,3‐triaryl‐2‐propen‐1‐ones. The Z isomers are found to give higher relative abundances of adduct ions than the E isomers. This has been interpreted in terms of the differences in the proton affinities of the isomers originating from their different degrees of enone resonance. Halide ion (CI− and Br−) attachment spectra of these compounds also show stereochemical differences in the relative abundances of [M]−˙ and [M+halide]− ions, though the effect is not as pronounced as in the case of the positive ion spectra.
1,2‐Carbon shifts in [C4H8O]+˙ and [C5H10O]+˙ ions
Authors: Hudson C. E. , McAdoo D. J.
Published: May 2005

Present results demonstrate that α,β‐shifts of the functional group carbon strongly dominate β,α‐methyl shifts in [C4H8O]+˙ and [C5H10O]+˙ ions, paralleling observations of others on methyl isobutyrate ions.
Multiple ionization, charge separation and charge stripping reactions involving polycyclic aromatic compounds
Authors: Kingston R. G. , Guilhaus M. , Brenton A. G. , Beynon J. H.
Published: May 2005

The 70 eV electron ionization mass spectra of polycyclic aromatic compounds are characterized by the presence of relatively stable multiply charged molecular ions [M]n+ (n=2–4). When generated from the compounds benzene, napthalene, anthracene, phenanthrene, 2,3‐benzanthracene, 1,2‐benzanthracene, chrysene, 9,10‐benzophenanthrene and pyrene, the relative abundances of the multiply charged ions increase dramatically with the number of rings. These compounds form multiply charged molecular ions (n=2, 3) which undergo unimolecular decompositions indicative of considerable ionic rearrangement. The main charge separation processes observed here [M]2+→m1++m2+, [M]3+˙→m3++m→+m42+) involve, in almost every case, one or more of the products [CH3]+, [C2H3]+˙ and [C3H3]+. This suggests the existence of preferred structures amongst the metastable parent ions. Information on the relative importance of the various fragmentation pathways is presented here along with translational energy release data. Some tentative structural information about the metastable ions has been inferred from the translational energy release on the assumption that the released energy is due primarily to coulombic repulsion within the transition state structure. For the triply charged ions these interpretations have necessitated the use of a coulombic repulsion model which takes account of an extra charge. Vertical ionization energies for the process [M]n++G→[M](n+1)+G+e− (charge stripping) have also been determined where possible for n=1 and 2 and the results from these experiments allow the derivation of simple empirical equations which relate successive ionization energies for the formation of [M]2+ and [M]3+˙ to the appearance energy of [M]+˙.
Hydrogen transfer in the retro‐Diels–Alder fragmentation of trans‐4‐amino‐, isopropyl‐amino‐, piperidino‐ and pyrrolidino‐2H‐1‐benzopyran‐3‐ols
Authors: Evans John M. , Gower John Leveson
Published: May 2005

The electron impact mass spectra of trans‐4‐amino‐, isopropylamino‐, pyrrolidino‐ and piperidino‐2H‐1‐benzopyran‐3‐ols show intense peaks corresponding to the retro‐Diels–Alder reaction. In addition significant ions due to hydrogen transfer to and from the retro‐Diels–Alder fragment ion are observed. The transfer of hydrogen to this retro‐Diels–Alder fragment ion is influenced by the nature and location of the aromatic substituents, and the amino group at C(4). The loss of hydrogen from the retro‐Diels–Alder ion is subject only to the nature of the amino group at C(4). Hydrogen transfer to the retro‐Diels–Alder ion is shown to arise from the gem‐dimethyl group at C(2), as it is attenuated by successive removal of the methyl groups.
Mass spectrometric studies on cyclo‐ and poly‐phosphazenes: 3—Polymerization of tris(o‐diphenylenedioxy)cyclotriphosphazene, [NP(O2C6H4)]3
Authors: Daolio Sergio , Traldi Pietro , Vecchi Enrico , Gleria Mario
Published: May 2005

The 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.
Distinction between 17‐epimeric hydroxy steroids of the 3,17‐dioxygenated androstane series by chemical ionization
Authors: Prome Danielle , Prome Jean‐Claude , Stahl Daniel
Published: May 2005

The 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.
Applications of charge stripping/charge exchange spectra of organic ions
Authors: Kingston E. E. , Beynon J. H. , Ast T. , Flammang R. , Maquestiau A.
Published: May 2005

The application of a new technique which involves the combination of charge stripping and charge exchange processes has been investigated. Ions are charge‐stripped in the second field‐free region of a triple‐sector mass spectrometer (BEE geometry), and then subjected to a charge exchange reaction in the third field‐free region. The resulting charge stripping/charge exchange (CS/CE) spectrum is free from interference, which is otherwise common in charge stripping spectra. Comparisons between charge stripping and CS/CE spectra are made in cases where both kinds of spectra are obtainable. In order to assess the applicability of this new technique to studies of isomeric ion structures, species for which charge stripping spectra have previously been unobtainable have been chosen. CS/CE spectra of [C6H6]+˙, [C6H5]+, [C8H10]+˙ and [C7H7O]+ ions from a variety of precursors are recorded: in most cases, sufficient differences are observed to permit distinction between isomeric structures (or mixtures of structures). Previous studies which have shown that stable doubly charged molecular ions of ethane cannot be formed by the charge stripping technique are confirmed from its CS/CE spectrum.
Structures and stabilities of [C3H3O]+ ions in the gas phase: A molecular orbital study
Authors: Bouchoux Guy , Hoppilliard Yannik , Flament Jean‐Pierre
Published: May 2005

The relative energies of 11 [C3H3O]+ ions are calculated by different molecular orbital methods (MINDO/3, MNDO, ab initio with 3‐21G and 4‐31G* basis set and configuration interaction). The four most stable structures are: a ([CH2CHCO]+), b
equation image
c ([CHCCHOH]+) and d ([CH2CCOH]+); their relative energies at the CI/4‐31G*//3‐21G level are 0, 117, 171 and 218 kJ mol−1, respectively. The isomerizations c→[CHCHCHO]+→[CH2CCHO]+→ a and dissociations into [C2H3]++CO and [HCO]++C2H2 are explored. The calculated potential energy profile reveals that the energy‐determining step is the 1,3‐H migration c→[CHCHCHO]+. This explains the value of unity of the branching ratio and the spread of kinetic energy released for the two dissociation channels.
A structural investigation of [C6H6]2+ and [C6H6]+˙ ions involved in charge exchange reactions
Authors: Guilhaus M. , Kingston R. G. , Brenton A. G. , Beynon J. H.
Published: May 2005

Mass‐analysed ion kinetic energy spectra for collisional activation (CA) of [C6H6]+˙ formed via electron capture by [C6H6]2+ ions in collision with neutral benzene molecules have been compared for the C6H6 isomers benzene, 1,5‐hexadiyne and 2,4‐hexadiyne. Comparisons of fragment abundance and total CA fragment yields were also made for [C6H6]+˙ ions generated by electron ionization (EI). CA conditions of ion velocity and collision gas pressure were identical in these comparisons. In general the fragment abundance patterns for the ions formed by charge exchange were very similar to those for singly charged benzene ions generated by EI. However, significant variations in CA fragment yield (the ratio of the total CA fragment ion abundance to the abundance of the incident unfragmented ions) were observed. It is not clear from the results whether these variations reflect structurally different ions or ions of different internal energies. The CA spectra of [C6H6]+˙ ions derived from charge exchange reactions between the benzene dication and the target gases He, Ne, Ar, Kr and Xe have also been recorded and, once again, very similar fragment abundance patterns were observed along with large variations in total CA fragment yields. Charge exchange efficiency measurements are reported for reactions between the benzene dication and the targets He, Ne, Ar, Kr, Xe and C6H6 (benzene) and also for the doubly charged ions derived from the linear C6H6 isomers. In the latter case Xe and benzene targets were used. The energetics and efficiency measurements for the former reactions suggest that for targets such as He and Ne the processes probably involve excited states of the doubly charged ions. The efficiencies measured for the latter reactions were distinctly different for the three C6H6 isomers and may indicate a strong dependence of charge exchange cross‐section on doubly charged ion structure.
Laser‐ion beam photodissociation studies of C4H4 radical cations
Authors: Krailler R. E. , Russell D. H.
Published: May 2005

The laser‐ion beam photodissociation for [C4H4]+˙ ions produced from a variety of precursors has been studied. Based on the data it is apparent that two structurally distinct forms of the [C4H4]+˙ ion are produced by fragmentation of larger systems. The relative population of the various structural forms is very dependent on the internal energy of the fragmenting ion, with 1‐buten‐3‐yne [C4H4]+˙ ions being favored at low internal energies. As the internal energy of the reactant ion is increased, the relative population of butatriene [C4H4]+˙ ions increases. The laser‐ion beam photodissociation technique is able to selectively sample these two structural forms.
Stable [C2H7O2]+ isomers: Experimental and theoretical evidence for the existence of protonated peroxides and proton‐bound dimers in the gas phase
Authors: van Driel Jan H. , Heerma Wigger , Terlouw Johan K. , Halim Herman , Schwarz Helmut
Published: May 2005

Evidence is presented for the gas phase generation of at least eight stable isomeric [C2H7O2]+ ions. These include energy‐rich protonated peroxides (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_2 {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (e), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm (H)OH} $\end{document} (f) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm (H)CH}_{\rm 3} {\rm (g)),} $\end{document} (g)), proton‐bound dimers (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm 3} \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} (h) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH2 = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm + } \cdot \cdot \cdot {\rm HOCH}_{\rm 3} $\end{document} (i)) and hydroxy‐protonated species (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} {\rm (OH)CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} (a), $\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH(OH)}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (b) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm OCH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (c)). The important points of the present study are (i) that these ions are prevented by high barriers from facile interconversion and (ii) that both electron‐impact‐ and proton‐induced gas phase decompositions seem to proceed via multistep reactions, some of which eventually result in the formation of proton‐bound dimers.
Gas phase reactions of chloride ion with aryl‐substituted nitrocyclohexenes
Authors: Das K. G. , Reddy A. Mahender , Mallaiah M. , Madhusudanan K. P.
Published: May 2005

Chloride ion chemical ionization studies of some aryl‐substituted nitrocyclohexenes have demonstrated that benzylic anion formation is favoured in the gas phase. Anchimeric assistance by neighbouring phenyl groups and the effect of olefinic functions have a significant influence on the stability of the carbanions.
Fragmentation of 1,4,5,8‐tetraazaphenanthrenes upon electron impact: A new example of structural integrity of gas phase heteroaromatic cations
Authors: Nasielski‐Hinkens Raymonde , Kaisin Michel , Flammang Robert , Maquestiau André
Published: May 2005

1,4,5,8‐Tetraazaphenanthrene and some derivatives have been studied by mass and ion kinetic energy spectrometries. Deuterium labelling experiments show an unexpected structural integrity of the gas phase molecular ions which eliminate H(D)CN, even near threshold energies (field‐free region reactions). The loss of N(1(8)) predominates largely over the loss of N(4(5)); the consecutive losses of H(D)CN are also highly specific. A similar specificty is observed for the chlorinated and methylated isomers. The atoms of the homocycle are not involved in the first steps of the fragmentation as indicated by the behaviour of 9‐chloro‐and 9‐methyl‐tetraazaphenanthrenes.
Thermospray mass spectrometry of diazonium and di‐, tri‐ and tetra‐quaternary onium salts
Authors: Schmelzeisen‐Redeker G. , Röllgen F. W. , Wirtz H. , Vögtle F.
Published: May 2005

Various diazonium, multiply charged ammonium and pyridinium salts and one diphosphonium salt have been analysed by thermospray (TSP) mass spectrometry. The intact cation forms the base peak in all spectra. Typically only a few, yet structurally significant, ions are observed. For diazonium salts the level of fragmentation can be controlled by the temperature of the TSP interface while the fragmentation of the quaternary salts is found to be rather insensitive to interface temperatures.
Electron impact and chemical ionization mass spectra of some tetra‐acetylated anomeric glycosides
Authors: Kulkarni P. S. , Kulkarni S. Y. , Pansare V. S.
Published: May 2005

Electron impact and chemical ionization (CH4, iso‐C4H10 and NH3) mass spectra of some tetra‐acetylated anomeric glycosides have been examined with a view to the characterization of anomeric pairs. Minor differences observed in the relative intensities of common ions in the anomeric pairs in the electron impact mass spectra are found to be enhanced in the methane and isobutane chemical ionization mass spectra. In the absence of thermal decomposition, the β‐anomers show greater ion abundances of common glycosyl ions than the α‐anomers. Ammonia chemical ionization mass spectra show complementary behaviour indicating strong adduct ions and practically no fragmentation.
Fragmentation of the chain in the mass spectra of the pyrrolidides of alkylcyclohexanecarboxylic acids
Authors: Vetter W. , Meister W.
Published: May 2005

The electron impact mass spectra of the pyrrolidides of both the cis‐ and trans‐octylcyclohexanecarboxylic acids show the structure of the aliphatic chain, despite the steric hindrance of a direct H transfer from the chain to the functional group.
Electron impact mass spectrometry of some macrocyclic and acyclic aldimines
Authors: Tamburini Sergio , Vigato Pietro A. , Traldi Pietro
Published: May 2005

The 70 eV electron impact mass spectra of some macrocyclic and acyclic aldimines, together with that of their synthon, are described and discussed with the aid of exact mass measurements, linked scans, deuterium labelling experiments and collisional experiments. The mass spectrometric behaviour of the acyclic compounds, not directly related to their structure, has been studied in detail with the aid of differential thermal analysis, which demonstrates the occurrence of pyrolysis.
Direct evidence for preformed ions of porphyrins in the solvent matrix for fast atom bombardment mass spectrometry
Authors: Musselman Brian D. , Watson J. Throck , Chang Chi K.
Published: May 2005

The observation that protonated molecules are present in solvents utilized for fast atom bombardment (FAB) mass spectrometric studies has been demonstrated using visible absorption spectrometry. Addition of porphyrins to thioglycerol, a solvent used for FAB analyses, results in partial protonation of the molecule. This reaction can be monitored by observing the shift in visible absorption maxima associated with the molecular transition from free base to protonated structure. A good correlation is observed between the degree of protonation indicated by the appropriate absorption bands and the abundance of the [M + H]+ ion in the FAB spectrum of the corresponding solution. Addition of certain non‐polar porphyrin molecules to thioglycerol does not result in the protonation of the molecule in solution; in these cases, analyses of the corresponding solutions by FAB do not yield [M + H]+ ions. Subsequent addition of trifluoroacetic acid to the solvent has proved sufficient to protonate the analyte molecule, as indicated by the visible absorption spectrum; FAB analyses of these non‐polar porphyins in acidified solvent result in the observation of [M + H]+ ions. These experiments demonstrate that analyses of these analyte molecules requires that they be present as ions in solution prior to analysis by FAB. This study provides experimental evidence for the presence of ions in solutions employed for FAB analysis, suggesting that these ions are essential for the generation of the protonated molecules observed during FAB mass spectrometric analyses.
The magic number nine‐atom alkali halide cluster ion. Is the nine‐atom planar structure the most stable?
Authors: Dunlap Brett I. , Campana Joseph E.
Published: May 2005

The question of whether the cubic structures proposed for the alkali halide cluster ions are the most stable has been re‐examined. Geometry/energy optimization calculations were performed on other candidate structures for the [M(MX)4]+ species. The square‐planar structure was found to be more than 3 eV lower in energy than a proposed quasi‐octahedral structure. The relative energies of the square‐planar and other structures for a series of nine‐atom alkali halide cluster ions are found to correlate with published experimental data.
Sulphonium ions: Collision‐activated dissociation using fast atom bombardment ionization and a triple quadrupole mass spectrometer
Authors: Mestdagh Hélène , Morin Nicole , Rolando Christian
Published: May 2005

The low‐energy collision‐activated dissociation of sulphonium cations, including symmetrical trialkyl R3S+, dimethylalkyl (CH3)2RS+, diphenylalkyl Ph2RS+ and cyclic (CH2)nS+R, has been recorded using fast atom bombardment ionization and a triple quadrupole mass spectrometer. The general trends are easy loss of sulphide to give [R]+, except for R  CH3, and loss of alkene to give protonated sulphide if β‐hydrogens are available. Loss of alkane, generally found in ammonium compounds, is not observed.
Intrinsic acidity and basicity of neutral and ionic species of some polyether‐ester compounds as shown by mass spectrometry
Authors: Podda Gianni , Corda Luciana , Maccioni Anna Maria , Traldi Pietro
Published: May 2005

The 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.
High energy collisional spectroscopy of [RCOO]− anions from negative ion chemical ionization of fatty acid methyl esters
Authors: Bambagiotti A. Massimo , Coran Silvia A. , Vincieri Franco F. , Petrucciani Tiziano , Traldi Pietro
Published: May 2005

Saturated and mono‐unsaturated fatty acid methyl esters as well as corresponding underivatized acids gave abundant carboxylate anions [RCOO]− under negative ion chemical ionization (OH− and NH2 −) and electron attachment conditions. B/E or mass‐analysed ion kinetic energy spectra of fragments arising from high energy collision activated dissociation (CAD) of these [RCOO]− species contained decisive information on the original structure of the neutrals. From an analytical point of view, the method can utilize the gas chromatographic mass spectrometric combination and, in the B/E mode, can be used in practice on any double‐focusing mass spectrometer.
Ion/molecule reaction inside the collision cell of a tandem quadrupole mass spectrometric system. 2. Energy dependence of ammonium ion formation
Authors: Schmit Jean‐Pierre , Beaudet Sylvie , Brisson Alain
Published: May 2005

The dependence of the protonation of neutral ammonia on the axial kinetic energy of protonated reactant ions has been studied in the gas phase, using various protonated carbonyl compounds, inside the collision cell of a tandem quadrupole mass spectrometric system. The hypothesis of two different and non‐competitive reaction channels has been proposed. The first is characterized by a very low (peaked at ±0.05 eVcm) and well‐defined axial kinetic energy of the reactant ion, while the second is more energy demanding (estimated threshold at ±0.2 eVcm) and expressed by a collisionally induced dissociation‐like energy curve. Fourier transform mass spectrometric experiments have shown that ammonium ion can be generated by direct proton exchange and fragmentation of the adduct ion obtained.
Mass spectral fragmentation pathways in nitroadamantanes. A tandem mass spectrometric collisionally induced dissociation study
Authors: Yinon J. , Bulusu S.
Published: May 2005

A collisionally induced dissociation study of adamantane, 1‐nitroadamantane, 1,3‐dinitroadamantane and 1,3,5,7‐tetranitroadamantane was carried out using tandem high‐resolution mass spectrometry. Fragmentation pathways of the compounds were determined in the electron impact mode. It was found that the fragmentation of all three nitroadamantanes begins with the consecutive losses of the NO2 groups followed by fragmentation of the hydrocarbon structure.
Low energy, low temperature mass spectra. 6—A synoptic view
Authors: Maccoll Allan
Published: May 2005

A review is presented of the low energy, low temperature mass spectra of a number of organic compounds, namely alkanes, alkanols, ethers, amines, alkanals, alkanones, alkanoic acids and alkanoic esters. The main fragmentation routes are described and the simplification of the mass spectra as compared with the 70 eV equivalents is emphasized.
Matrix effects in negative‐ion field desorption mass spectrometry
Authors: Röllgen F. W. , Dähling P. , Bramer‐Weger E. , Okuyama F. , Subhan M.
Published: May 2005

The negative ion mode of field desorption mass spectrometry is matrix dependent. The matrix is used to facilitate the desolvation of ions at field strengths below the onset of field induced electron detachment. The role of the matrix in the desolvation mechanism for negative ions is briefly described and the main properties of a matrix solution, such as viscosity, solubility for complex salts and acids, and adhesion to the emitter surface, on the ion formation are discussed. The application of matrix mixtures with strong adhesion to the emitter surface even at elevated temperatures and high field strengths are considered to be important for the further improvement of this ionization method.
A general soft ionization method for mass spectrometry: Resonance‐enhanced multi‐photon ionization of biomolecules
Authors: Grotemeyer Jürgen , Boesl Ulrich , Walter Klaus , Schlag Edward W.
Published: May 2005

We show here that ‘double‐barrelled’ laser desorption/resonance‐enhanced multi‐photon ionization mass spectrometry has many advantages over traditional single‐step desorption/ionization techniques, particularly if combined with Reflectron‐Time‐of‐Flight mass analysers. We demonstrate the effectiveness of this technique for large labile biomolecules, namely native chlorophylls, porphyrins and a peptide, as examples of structural and mass analysis.
Desorption ionization combined with tandem mass spectrometry: Advantages for investigating complex lipids, disaccharides and organometallic complexes
Authors: Cerny Ronald L. , Tomer Kenneth B. , Gross Michael L.
Published: May 2005

Combining desorption ionization with tandem mass spectrometry overcomes the disadvantage of limited fragmentation accompanying desorption and permits mixtures of closely related substances to be investigated directly. These features of the combination are illustrated by completing the structure‐proof of a minor component of an ornithine‐containing lipid mixture isolated from Thiobacillus thiooxidans. The minor component is a homolog of the major constituent and differs from the principal component owing to the presence of a double bond in lieu of a cyclopropyl ring in one of the constituent fatty acids. Another feature of the combined method is the potentially complementary nature of collision‐activated dissociation spectra of protonated and cationized biomolecules. This is illustrated by the differences in the collision‐activated dissociations of the [M + Na]+ of sucrose, desorbed by field desorption, and [M + H]+, desorbed by fast atom bombardment. A third illustration is the application of field desorption and tandem mass spectrometry to an organometallic compound. The combined approach allows the ligands to be identified and the relative ligand binding energies to be approximated.
Fragmentations of protonated benzaldehydes via intermediate ion/molecule complexes
Authors: Filges U. , Grützmacher Hans‐Fr.
Published: May 2005

Ions ap and am corresponding to protonated p‐ and m‐methoxymethylbenzaldehydes have been generated in a mass spectrometer by electron impact fragmentation of the correspondingly substituted 1‐phenylethanols (1 and 2). Metastable ions ap and am (2nd FFR of a VG‐ZAB‐2F mass spectrometer) react by elimination of CH3OH, loss of HCOOCH3, formation of ions CH2=OCH3 and to a small extent by loss of CH2O and CH3OCH3, respectively. The mechanisms of these reactions have been studied by extensive D‐labelling, and it is shown that these fragmentations are initiated by a transfer of the proton located originally at the carbonyl group onto the aromatic ring. The formation of ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_2 = \mathop {{\rm OCH}_3 }\limits^ + $\end{document} and the loss of CH3OH occurs via π‐and σ‐complexes. The elimination of HCOOCH3 from ions ap and am corresponds to a functional group interaction between distal side chains and occurs via intermediate ion/molecule complexes formed by a protolytic cleavage of the formyl group. The loss of CH2O and CH3OCH3 proceeds also by intermediate ion/molecule complexes which are generated by a protolytic cleavage of the methoxymethyl side chain in ions ap and am.
Structure and formation of gaseous [C3H4N]+ ions
Authors: Heerma Wigger , Sarneel Maria M. , Dijkstra Geo
Published: May 2005

magnified imagegas phase has been established. This conclusion could be derived from a careful study of their collisional activation spectra, which show minor but characteristic differences. The ions studied were generated from various precursor ions in single or multiple fragmentation processes as well as via ion‐molecule reactions. Their heats of formation vary from 925 to 1085 kJ mol−1 according to MINDO/3 or from 925 to 1050 kJ mol−1 according to MNDO calculations.
Mass spectrometry of some dichloroacetamides of pharmacological interest. Evidence for an unusual skeletal rearrangement
Authors: Arlandini E. , Gioia B. , Pella E. , Tonani R. , Traldi P.
Published: May 2005

The mass spectrometric behaviour of six N‐(2‐ethoxyethyl)‐N‐p‐substituted benzyldichloroacetamides is described and discussed in detail with the aid of exact mass measurements, metastable analysis and mass‐analysed ion kinetic energy spectrometry. The presence of an unusual skeletal rearrangement is described.
Positive and negative ion fast atom bombardment mass calibration using concentrated H2SO4
Authors: Sharp Thomas R.
Published: May 2005

Concentrated H2SO4 has proved to be an extremely useful calibrant for both positive ion and negative ion FAB mass spectrometry. It is a single compound, commonly found in any laboratory, and presents a clean, simple spectrum, with only approximately 100 peaks needed to achieve calibration up to at least m/z 1500.
Application of low energy CID in the determination of structures of [M – halogen]+ ions obtained from diethyl halosuccinates under electron impact
Authors: Weisz A. , Mandelbaum A. , Blum W. , Domon B. , Muller D. , Richter W. J. , Shabanowitz J. , Hunt D. F.
Published: May 2005

Low energy collision induced dissociation (CID) spectra indicate that m/z 173 ions formed by the loss of a halogen atom from diethyl chloro‐ and bromo‐succinate under electron impact are mixtures of O‐protonated diethyl maleate (>90%) and fumarate (<10 %). Hydrogen migration precedes the C‐halogen bond cleavage in these cases. The low energy CID spectrum of the m/z 173 [MI]+ ion obtained from diethyl iodosuccinate shows that only a small fraction of the [MI]+ ions are the O‐protonated species formed by hydrogen migration. The results of this study demonstrate the potential of low energy CID in the determination of structure (including configuration) of gas phase ions.
Carbanion rearrangements. Collison induced dissociations of deprotonated alkyl acetoacetates
Authors: Eichinger Peter C. H. , Bowie John H.
Published: May 2005

Deprotonation of methyl acetoacetate yields two enolate ions MeCOC̄HCO2Me (a) and C̄H2COCH2CO2Me (b). On collisional activation, ions a and b fragment differently. The major fragmentation of a is specific loss of MeOH through a four‐centred transition state to form −O(Me)CCCO. In contrast, ion b eliminates CH2CO to give −CH2CO2Me. Some rearrangement of b to a is also noted. Rearrangement of a to b is very minor under single collision conditions but at high collision gas pressure rearrangement of a to b is strongly promoted. Similar effects are observed in the collisional activation spectra of MeCOC̄(Me)CO2Me (c) and −CH2COC(Me)CO2Me (d). The loss of MeOH from (c) proceeds via a six membered transition state to −CH2COC(Me)CO; this is a stepwise process in which the deprotonation (step two) is not rate determining. A number of other decompositions occur, these have also been studied by deuterium labelling.
Reaction of ammonia with accelerated benzoyl ions under multiple‐collison conditions in a triple quadrupole instrument
Authors: White Earl L. , Tabet Jean‐Claude , Bursey Maurice M.
Published: May 2005

The reaction of benzoyl ion with ammonia in multiple‐collision conditions in the second quadrupole assembly of a triple quadrupole mass spectrometer at (laboratory) ion kinetic energies from 0 to 20 eV produced the even‐electron ions [C6H5]+, [C6H5NH3·(NH3)m]+ (m = 0, 1) and [C6H5CONH3·(NH3)n]+ (n = 0, 1, 2, 3) and the odd‐electron ions [C6H4NH3·(NH3)p]+· (p = 0, 1). Thermochemical information could not be obtained under multiple‐collision conditions: both exothermic and endothermic reactions were observed, with no translational‐energy onset measurable for the endothermic processes, nor decrease in the yield of the exothermic processes at high energies. The behaviour of cluster‐ion intensities as pressure varied was qualitatively as expected. There are pressure and energy regions where spectra change little; if this feature were to be general, it would point to some utility for these conditions in qualitative analysis.
Electron impact mass spectrometry of some macrocyclic polyether lactones
Authors: Podda Gianni , Corda Luciana , Anchisi Carlo , Pelli Beatrice , Traldi Pietro
Published: May 2005

Electron impact mass spectrometry has been used together with linked scans, exact mass measurements and mass‐analysed ion kinetic energy spectrometry to study nine inacrocyclic polyether lactones in detail. The presence of abundant hydrogenated oxirane ions has been observed for all the compounds examined, and confirmed by kinetic energy release measurements.
On the unimolecular loss of acetylene from metastable C11H9]+ ions
Authors: My Nguyen Kieu , Schwarz Helmut
Published: May 2005

Extensive 13C labelling experiments demonstrate that loss of acetylene from metastable [C11H9]+ ions is a complex process, which can be described quantitatively in terms of a four‐parameter model. The major reaction path (77.8%) involves scrambling of all 11 carbon atoms. Insight into the reaction details is provided neither by the kinetic energy release associated with the reaction [C11H9]+ → [C9H7]+ + C2H2 nor by the analysis of the collisional activation mass spectra of the resulting [C9H7]+ ions.
Fractional mass values of large molecules
Authors: Pomerantz Steven C. , McCloskey James A.
Published: May 2005

From the standpoint of relative molecular mass (RMM) determination by mass spectrometry, the average relative molecular masses of organic molecules in the range over 2000 daltons are significantly influenced both by the fractional masses of the constituent elements and by natural variations in isotopic abundance. Differences between monoisotopic RMM and relative atomic mass (RAM) based RMM tend characteristically to differ between major classes of biomolecules primarily because of molar carbon content, the difference between polypeptides and nucleic acids being about 4 daltons at Mr = 25 000. Considering terrestrial sources alone, variations in the isotopic abundance of carbon lead to differences of about 10–25 ppm in average molecular mass, which is significant with respect to present mass measurement capability in the region up to several thousand daltons. Comments are made concerning the calculation of average RMM values horn isotopic probability profiles versus those from RAMs.
Gas‐phase derivatization of [C3H5]+ ions using tandem mass spectrometry methods A13C labelling study
Authors: My Nguyen Kieu , Schilling Marita , Schwarz Helmut
Published: May 2005

The study of specifically 13C‐labelled precursors sheds further light on the gas‐phase chemistry of allyl and 2‐propenyl cations. It is demonstrated that both species are formed from allyl and 2‐propenyl bromide upon 70 eV electron impact ionization without skeletal reorganization. Gas‐phase derivatization of the [C3 H5]+ ions with benzene facilitates, as suggested and observed earlier, the distinction of the two isomers using collision‐induced dissociation of the Wheland complexes (or isomers thereof). The 13C labelling data clearly demonstrate that 64% of allyl cations survive the derivatization while 36% isomerize to 2‐phenylpropyl cations; the latter are also formed via the reaction of 2‐propenyl cation with benzene, protonation of α‐methylstyrene and water loss from protonated 2‐phenyl‐2‐propanol, respectively. Unimolecular loss of C2H4 from protonated allylbenzene proceeds via two competing reaction channels: one involves heterolysis of 1‐phenylpropyl cations (∼30%); the major pathway (∼70%), however, involves decomposition via propylene benzenium ions.
Stereochemical applications of mass spectrometry 4. Energy‐resolved study of the fragmentation of esters of maleic and fumaric acids
Authors: Harrison Alex G. , Nacson Sabatino , Mandelbaum Asher
Published: May 2005

The fragmentation of the dimethyl and diethyl esters of maleic and fumaric acids have been studied as a function of the internal energy of the molecular ions using charge exchange techniques and metastable ion studies in combination with isotopic labelling. The dimethyl ester molecular ions show distinctive behaviours at both low and high internal energies, indicating that interconversion of the molecular ions does not occur. The fumarate molecular ion fragments by elimination of CH2O and (CO2 + CH3) in the metastable ion time‐frame, while the maleate ester fragments primarily by loss of CH3O. At higher internal energies both molecular ions fragment primarily by loss of CH3O but the fragment ion from the maleate ester shows a greater stability, presumably because it assumes the cyclic cationated maleic anhydride structure. The diethyl maleate and diethyl fumarate molecular ions show identical metastable ion characteristics; in addition the [COS]+· charge exchange mass spectra are very similar. These results indicate that low‐energy molecular ions interconvert. At higher internal energies interconversion does not occur, and, although both moiecular ions fragment by loss of C2H5O, the resultsint fragment ions show different stabilities and fragmentation reactions.
A study of the electron capture induced decompositions and charge separation reactions of the doubly charged isomeric ions of the methylpyridines and aniline
Authors: Curtis J. M. , Vékey K. , Brenton A. G. , Beynon J. H.
Published: May 2005

The doubly charged isomeric ions [C6H7N]2+ formed from 2‐, 3‐ and 4‐methylpyridine and aniline were investigated via their unimolecular charge separation reactions and by electron capture induced decompositions (ECID). The ECID spectra were compared with the collision induced decomposition (CID) spectra of the singly charged ions in an attempt to investigate the structure of the doubly charged ions. The four isomers could be unambiguously identified by their unimolecular charge separations. These differences were greater than in the mass spectra, ECID spectra or CID spectra of singly charged ions.
The reaction intermediate spectrum. A new type of experiment in tandem mass spectrometry
Authors: O'Lear John Raymond , Wright Larry Gene , Louris John Nathan , Cooks R. Graham
Published: May 2005

A new scan is described which responds to ions that are intermediates in the dissociation of a mass‐selected parent ion (mp) to give a mass‐selected daughter ion (md). The scan gives a simple mass v. abundance output for ions which satisfy this condition. It is implemented here on a BEQQ hybrid mass spectrometer using, in sequence, collision‐induced dissociation occurring at high energy in the first reaction region, and low‐energy collisional activation in the collision quadrupole. The experiment provides information on reaction sequences not available from single scans of other types. In the several cases examined, it is demonstrated that, among many conceivable fragmentation routes connecting a parent ion with a particular fragment ion, only a few are significant. Examination of reaction intermediate spectra also appears to be a fruitful new approach to mechanistic questions, as illustrated by consideration of the behavior of several isomeric octanones. These new spectra also have analytical value: they show good signal‐to‐noise ratios and allow ready distinction between isobaric and isomeric ions. A comparison of the reaction intermediate spectrum with a daughter spectrum obtained by the B/E linked‐scanning technique reveals the contributions of artifact peaks which result from poor parent ion mass resolution in the latter. Reaction intermediate spectra combine information from the daughter spectra of mp and the parent spectra of md and, as a specified portion of this data domain, have unique characteristics.
Nucleophilic substitution in certain bicyclic sesquiterpene alcohols under chemical lonization conditions
Authors: Madhusudanan K. P. , Srivastava Rashmi , Kulshreshtha D. K. , Fraisse D.
Published: May 2005

Substitution of amino for hydroxyl groups in certain sesquiterpene alcohols has been studied by chemical ionization mass spectrometry using ammonia and ammouia‐d3 as the reagent gases, and by mass‐analysed ion kinetic energy spectrometry and collision‐induced decomposition mass‐analysed ion kinetic energy measurements. Depending upon the source conditions and the nature of the substrates, both SNi and SN1 mechanisms have been found to operate. No evidence is obtained for an SN2 mechanism in these compounds. In centdarol and isocentdarol, addition of NH3 to the double bond, followed by elimination of H2O, also contributes to the substitution process. Attack of [NH4]+ on the epoxide function, followed by loss of H2O, appears to lead to the substitution ions in epoxycentdarol, epoxyisocentdarol and epoxyhimachalol.
Unimolecular dissociations of the [2‐hexanone]+˙ metastable ion
Authors: Bouchoux Guy , Tortajada Jeanine , Dagaut Jacques , Fillaux Joëlle
Published: May 2005

The metastable molecular ion of 2‐hexanone loses a methyl radical mainly (∼80%) from positions C(4) and C(6), in equal proportions, as indicated by 13C labelling. The necessary skeletal rearrangement of the butyl chain is interpreted in terms of a 1,2‐[enol‐olefin] +˙ shift. The results and the mechanisms concerning the minor eliminations of C2H4, C2H5˙, C3H5˙ and C3H6 neutrals are also discussed.
Mass spectral fragmentation of benzofurazan‐1‐oxide
Authors: Dyall Leonard K.
Published: May 2005

Fragmentations in the mass spectrum of benzofurazan‐1‐oxide have been studied using linked scan, accelerating voltage scan and mass‐analysed ion kinetic energy spectrometric techniques. Major pathways involve NO·+ NO· and NO·+CO loss, these double losses occurring in such rapid succession as to appear ‘concerted’ in some experiments. Minor pathways are loss of CO2, C2N2O2, or C2HN2O2 from the molecular ion. The major fragment ion, m/z 76, in the conventional mass spectrum is not detected in a mass‐analysed ion kinetic energy spectrometric experiment with the molecular ion until collision activation is provided. The conventional electron impact spectrum invariably includes ions from benzofurazan which is produced by thermal deoxygenation in the source.
Average mass approach to stable isotope dilution mass spectrometry
Authors: Blom Karl F.
Published: May 2005

The application of the fundamental equation for isotopic dilution mass spectrometry to real samples often requires using approximations which can lead to significant errors. A new approach relating the composition of isotopic mixtures to the average mass of the mass spectral pattern is presented. The fundamental equations are completely general; they should be applicable to a wide range of problems and may provide improved accuracy and precision in some cases.
Energy dependence of the fragmentation of ester enolate ions
Authors: Young Alex B. , Harrison Alex G.
Published: May 2005

The energy dependence of the fragmentation of a selection of ester enolate ions has been studied by variable, low‐energy collision‐induced dissociation experiments in the quadrupole collision cell of a hybrid BEQQ mass spectrometer. The dominant fragmentation reactions observed are
equation image
where ΔH1 − ΔH2=PA([RCCO]−) − PA([ŔO]−) (PA=proton affinity). The anion of lowest proton affinity is formed preferentially at low internal energies with the yield of the anion of higher proton affinity increasing with increasing internal energy. The [CH3OCOCOCH2]− anion derived from methyl pyruvate forms [CH3OCO]− by reaction (2); this anion readily fragments to [CH3G]−+ CO consistent with a structure represented by a dipole‐stabilized cluster of [CH3O]− and CO.

Comparison of the 8‐keV with the 50‐eV collision‐induced dissociation mass spectra indicated that the average internal energy of the fragmenting ions is considerably lower in the high‐energy collisional experiments than it is in the low‐energy collisional experiments.