bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass spectrometry of pancuronium bromide and related quaternary ammonium steroids using the moving belt LC/MS interface
Authors: Baker Timothy R. , Vouros Paul , Martyn Jeevendra A. J.
Published: May 2005

Pancuronium and vecuronium are members of a series of quaternary ammonium steroids used as neuromuscular blocking agents in anesthesiology. In this study the mass spectrometric properties of these bromide salts are examined and spectral features which permit their differentiation are evaluated. The relative merits of chemical ionization and fast atom bombardment using the moving belt liquid chromatography/mass spectrometry interface have been investigated. Fragmentation pathways for both ionization methods were determined with deuterium labeling and linked‐scan techniques. Cleaner spectra can be obtained via the matrix‐free belt introduction system as compared to conventional fast atom bombardment.
Gas chromatography/electron impact mass spectrometry applied to the differentiation of the positional isomers of long‐chain n‐alkylcyclohexanones
Authors: Rontani J.‐F. , Giusti G.
Published: May 2005

The influence of n‐butyl group position upon the fragmentation behavior of the three isomeric n‐butylcyclohexanones was studied. The different fragmentation processes are described and have been applied to the differentiation of the positional isomers of long‐chain n‐alkylcyclohexanones. In the case of the 4‐n‐alkyl isomers, an interesting mechanism involving a recyclization is proposed and substantiated by deuterium labelling.
FAB and chemical ionization in the production of [M+ H]+ and [M− H]− species from 2‐aryl‐2‐methyl‐1,3‐dithianes
Authors: Sturaro Alberto , Traldi Pietro , Paradisi Cristina
Published: May 2005

The unimolecular fragmentations of [M + H]+ and [M – H]− ions from four 2‐aryl‐2‐methyl‐1,3‐dithianes are described and clarified with the aid of deuterated derivatives. Comparison of the MIKE spectra of [M + H]+ species obtained under chemical ionization and fast atom bombardment (FAB) conditions reveals differences which are attributed to the different energetics involved in the two ionization processes. It is suggested that FAB is a ‘softer’ ionization technique but, at the same time, it provides, for the possibility of solvation, reaction sites not available in gas‐phase protonation. [M – H]− species and anionic fragments thereof were generally not obtained under FAB(−) conditions. [M – H]− ions are readily produced in gas‐phase reactions with OH− via proton abstraction from C(4) or C(5), and from the 2‐methyl substituent; and they fragment according to several reaction pathways.
Structural characterization of organic molecules by negative ions in laser microprobe mass spectrometry. Part 1—Neutral compounds
Authors: Van Vaeck L. , Bennett J. , Van Epsen P. , Schweikert E. , Gijbels R. , Adams F. , Lauwers W.
Published: May 2005

Laser microprobe mass spectrometry (LMMS) has been used to systematically study polyfunctional molecules, covering a wide range of structure and polarity. The knowledge about the mechanisms actually involved for desorption and ionization (DI) of organics by laser microbeam irradiation of solid samples at high‐power density is rather limited. Therefore we have elaborated a set of tentative hypotheses about DI in LMMS, permitting consistent rationalization of detected signals. The technique apparently combines desorption under mild conditions, shown by the release of intact thermolabiles, with extensive fragmentation. Structural data are typically distributed between cations and anions. Interpretation of negative‐ion detection mode mass spectra often represents intricate problems, partly due to the lack of sustaining background information from conventional mass spectrometry. Selected examples are presented to illustrate the occurrence of electron capture ionization, the role of heteroatoms in the formation of negative ions and the tendency to undergo complex skeletal rearrangements. Although LMMS was originally aimed at microprobe applications, it has been found to be a valuable tool in organic mass spectrometry.
Chemical ionization and collisional activation spectra of α,β‐unsaturated nitriles
Authors: Madhusudanan K. P. , Murthy V. S. , Fraisse D.
Published: May 2005

A study of the chemical ionization (CI) and collisional activation (CA) spectra of a number of α, β‐unsaturated nitriles has revealed that the even‐electron ions such as [MH]+ and [MNH4]+ produced under chemical ionization undergo decomposition by radical losses also. This results in the formation of M +˙ ions from both [MH]+ and [MNH4]+ ions. In the halogenated molecules losses of X˙ and HX compete with losses of H˙ and HCN. Elimination of X˙ from [MH]+ is highly favoured in the bromoderivative. The dinitriles undergo a substitution reaction in which one of the CN groups is replaced with a hydrogen radical and the resulting mononitrile is ionized leading to [M  CN + 2H]+ under CI(CH4) or [M  CN + H + NH4] and [M  CN + H + N2H7]+ under CI(NH3) conditions.
Rearrangements in aryl substituted α, β‐unsaturated nitriles. A collisional activation study
Authors: Madhusudanan K. P. , Murthy V. S. , Fraisse D.
Published: May 2005

The rearrangement reactions following electron ionization in a number of aryl substituted conjugated nitriles have been studied using labelled compounds and collisional activation (CA) spectroscopy. The results indicate that α‐phenyl cinnamonitriles and 9,10‐dihydro‐9‐cyanophenanthrene rearrange to a common intermediate which loses CH3˙ or CH2CN˙ to give the ions at m/z 190 and 165. The CA spectrum of the deuterated analogue (compound 2) shows that there is a complete hydrogen scrambling prior to the loss of the CH3˙ radical. The fluoroderivatives (compounds 5 and 6) behave similarly to the parent nitrile. The introduction of chlorine or bromine into the aromatic ring alters the fragmentation pattern and the only favoured decomposition pathway is the loss of a halogen radical. The CA spectra of the doubly charged ions at m/z 102 and 88 are also discussed. The CA spectrum of the M +˙ ion 1,1‐dicyano‐2‐phenyl ethylene is characterized by the presence of a rearrangement ion atm/z 103 (PhCN+ ˙).
Fragmentation of 1‐aryl‐5‐(2‐dialkylaminovinyl)‐1H‐tetrazoles upon electron impact
Authors: Herrmann Michael , Fischer Gerhard W.
Published: May 2005

The mass spectrometric behaviour of 1‐aryl‐5‐(2‐dialkylaminovinyI)‐lH‐tetrazoles was studied, especially 1‐phenyl‐5‐(2‐dimethylaminovinyl)‐l H‐tetrazole as a typical example of D‐ and 15N‐labelled derivatives revealed a rearrangement via a carbodiimide‐like intermediate ion.
Influence of reversed‐ and normal‐phase liquid chromatographic eluents in the fragmentation of selected chlorinated herbicides in thermospray liquid chromatography‐mass spectrometry
Authors: Barceló Damià
Published: May 2005

The effect of two completely different mobile phase compositions, reversed‐phase acetonitrile‐water + ammonium acetate and normal‐phase cyclohexane, were compared in filament‐on thermospray liquid chromatography‐mass spectrometry (LC‐MS) for the determination of selected chlorinated herbicides such as chloroatrazines and chlorinated phenoxyacetic acids. By using acetonitrile‐water + 0.05 M ammonium acetate mixtures in positive ion mode thermospray LC‐MS, the chloroatrazine herbicides showed the acetonitrile adduct ion [M + (CH3CN)H]+ as the base peak, whereas the chlorinated phenoxyacetic acids showed no signal. In contrast, when cyclohexane, which is reported for the first time as an eluent in the thermospray technique, was used as the mobile phase the chlorinated phenoxyacetic acid herbicides exhibited [M – H]+, [M – Cl]+ and M+˙ as the main ions.

Negative ion mode thermospray LC‐MS showed [M – H]− as the base peak for the chloroatrazines in the different mobile phases, whereas the chlorinated phenoxyacetic acids exhibited [M + H]−, [M + Cl]− or [M – HCl]− as the base peaks in cyclohexane and [M + acetate]− in acetonitrile‐water‐ammonium acetate.
Electron impact induced fragmentation of β‐allenic and γ‐acetylenic alcohols
Authors: Arseniyadis Siméon , Maquestiau André , Flammang Robert , Guenot Pierre , Carrié Robert
Published: May 2005

The main fragmentation pathway of ionized hydroxyallenes (1) consists of a methyl loss. Extensive deuterium‐labelling experiments indicate that the terminal allenic carbon is implied in this fragmentation. Collisional activation spectra indicate a propenyl‐acylium structure (a) for these [M – CH3]+ ions which can originate from a 1,4‐hydroxyl migration followed by hydrogen rearrangements. Isomeric hydroxyacetylenes (2) behave similarly, also giving rise, by methyl loss, to acylium ions a. It is proposed that 2+ ˙ is irreversibly isomerized into 1+ ˙ by a 1,3‐hydrogen transfer ‘catalysed’ by the hydroxy group. The proposed internal proton‐bound complex justifies also the easier loss of water from 2+˙. Ethyl loss is also a prominent fragmentation for the hydroxyallene and hydroxy‐acetylene homologues.
The unimolecular fragmentation of steroidal amides under electron impact. The role of intermediary ion‐neutral complexes
Authors: Longevialle Pierre , And Guy Bouchoux , Hoppilliard Yannik
Published: May 2005

The neutral fragment produced in the main decomposition process of 3‐amido steroids after electron impact is shown, by thermochemical arguments, to have the amide structure rather than enolamide as would be expected from a simple McLafferty rearrangement. It is proposed that the enolamide to amide tautomerization takes place during the decomposition process involving ion‐neutral complexes, and is responsible for the lack of regioselectivity in the origin of the hydrogen transferred. An energy barrier of unknown origin is shown to exist in the formation of the accompanying [amide + H]+ ion.
Characteristic fragmentations of peptide derivatives containing proline in negative‐ion fast atom bombardment mass spectrometry
Authors: Tsunematsu Hideaki , Nakashima Shizuko , Yamamoto Magobei
Published: May 2005

Fragmentations of N‐benzyloxycarbonyl‐protected tripeptide ethyl esters containing proline were compared with those of the corresponding peptide derivatives not containing proline in negative‐ion fast atom bombardment mass spectrometry. The fragment ion [M – 109]− due to loss of the benzyloxy group followed by dehydrogenation from the peptide molecule was the base peak in the negative‐ion mass spectra for the peptides not containing proline, whilst it was a very weak fragment ion or not observed at all in those for the peptides containing proline. These results suggest that the fragmentations of the peptide derivatives in negative‐ion fast atom bombardment mass spectrometry depend on the conformational difference of the peptide derivatives owing to the existence of proline in the derivative.
MNDO study of fragmentations in mass spectrometry. Part I. The geometry and electron structure of [C3H6O] + ˙ systems and [C2H3O]+ ions
Authors: Hrušák Jan , Tkaczyk Martin
Published: May 2005

MNDO calculations of [C3H6O]+ ˙ predict the parallel existence of both structures of radical cations of acetone (1) and propen‐2‐ol (2) in electron ionization spectra. The calculated heats of formation of 1+ ˙ (ΔHfMNDO = 783.2 kj mol−1) and of 2+ ˙ (ΔHfMNDO = 649.8 kJ mol−1) are in very good agreement with the experimental results. A comparison with the results of ab initio calculations (3–21 G and 6–31 G) and experimental data for the individual structures of the main fragment [C2H3O]+ demonstrates a sufficient accuracy of MNDO results, suggesting the possibility of applying the method also in other cationic systems, especially in larger ones.
Chemical ionization mass spectrometry with amines as reactant gases. VII—Amine chemical ionization mass spectrometry of some iridoid and secoiridoid glucosides
Authors: Mollova N. N. , Handjieva N. V. , Popov S. S.
Published: May 2005

The chemical ionization mass spectra of iridoid glucosides of the loganin type and secoiridoid glucosides of the gentiopicroside type were investigated. Triethylamine, diethylamine, ethylenediamine and ammonia were used as reactant gases. The possibilities of establishing the relative molecular masses and the masses of both the sugar residue and the aglycone and some structural and stereochemical features are discussed.
Electron ionization mass spectra of novel 2,3:4,5‐bis‐O‐(1‐methylethylidene)‐β‐D‐fructopyranose derivatives and related sugar sulfamates
Authors: Caldwell Gary W. , Sorgi Kirk L. , Scott Lorraine , Maryanoff Bruce E. , Maryanoff Cynthia A. , Masucci John A. , Nortey Samuel O. , Sisco William R. , Micheel Arthur , Ko Chan‐Yan
Published: May 2005

The electron‐impact (EI) mass spectral fragmentation of ten bis‐O‐ (1‐methylethylidene)fructopyranose derivatives and three related sugar sulfamates were investigated. In particular, 2,3:4,5‐bis‐O ‐ (1‐methylethylidene)‐β‐D‐fructopyranose sulfamate (topiramate), a potent anticonvulsant, was examined in greater detail. The fragmentation of the 2,3:4,5‐bis‐O‐(1‐methylethylidene) fructopyranose derivatives in general was not very dependent on the nature of substitution; the mechanisms of the common and unique fragmentation patterns are presented. These compounds showed characteristic peaks at m/z [M – 15]+, [M – 15 – 58]+, [M – 15 – 58 – 60]+, [M  CH2X]+ and [M  CH2X – 58]+ where X = OSO2NR2 (R  H, CH3, and/or Ph), OC (O)NHR, NH2, CI and OH. The fragmentation of isomeric bis‐O‐(1‐methylethylidene) derivatives of aldopyranose, ketopyranose and ketofuranose sulfamates was also investigated. The results indicate that isomeric sugar sulfamates can be easily distinguished in the EI mode. Key fragmentation pathways are discussed for these compounds.
Obtaining structural information on perfluorocarbons by mass spectrometry II‐charge‐exchange method
Authors: Huang Sunkwei
Published: May 2005

Structural and molecular ion information on perfluorocarbons (PFCs) can be obtained by charge‐exchange reactions of nitrogen or oxygen radical cations with PFCs; such information usually cannot be obtained by the electron impact or negative ion chemical ionization methods. Charge‐exchange reactions occurred when 0.5‐1.0 Torr (1 Torr as 133.3 Pa) of nitrogen, air or other gases was introduced into the chemical ionization source of a mass spectrometer, with electron energies ranging from 55 to 230 eV. Changing the repeller voltages and electron energies had little effect on the appearance of charge‐exchange mass spectra of PFCs. However, when air or nitrogen was introduced in the direction opposite to sample flow, more intense molecular ions and/or higher mass fragment ions were obtained at the cost of a small loss of sensitivity. The charge‐exchange mass spectrum of perfluoro‐1,3‐dimethyladamantane is very similar to the high‐energy collisionally induced dissociation spectrum of its molecular radical cation. This technique provides an important validation tool without the use of tandem mass spectrometry for the structure determination of PFC isomers.
Formation of negative ions of monosubstituted group VIB pentacarbonyls during fast atom bombardment mass spectrometry
Authors: Van Breemen Richard B. , Martin LeRoy B. , Schreiner Anton F.
Published: May 2005

The first negative‐ion fast atom bombardment mass spectra of a related series of monosubstituted Group VIB transition metal pentacarbonyls, M(CO)5L (M = Cr), Mo or W and L = P(Ph)3, As(Ph)3 or Sb(PH)3), have been obtained. Instead of molecular ion radicals, pseudomolecular adduct ions, [M + H]− and [M + 15]−, were detected, with the hydride species being much more abundant. High‐resolution measurements and comparison of observed isotope clusters with computer‐generated theoretical isotope patterns confirmed that ionization occurred by several mechanisms, including electron capture, charge dissociation and formation of adducts with charged species. Fragmentation consisted primarily of elimination of neutral ligands, i.e. ([MH ‐ L]−, [MH ‐ CO]−, [MH ‐ 2CO]−, etc. B/E and constant neutral loss linked scanning with collisional activation were used to confirm fragmentation pathways and characterize the site of hydride attachment on the transition metal complex. The information obtained demonstrates the utility of fast atom bombardment mass Spectrometry in the analysis of metal carbonyls.
Optimized production of the acylium diagnostic ions in the chemical ionization NO+ mass spectra of long‐chain monoolefins
Authors: Einhornt J. , Malosse C.
Published: May 2005

A recent reinvestigation of the reactivity of NO+ towards straight‐chain monoolefinic compounds revealed that the characteristic acylium ions, previously reported for alkenyl acetates and related compounds, could also be obtained from alkenes and alkenoic acids (or esters). In this study, the influence of the sample pressure and that of NO on the production of the acylium ions was investigated, leading to disappearance graphs indicative of a strong dependence on these experimental factors. This gives a further explanation for previous apparent discrepancies in the literature and the optimum conditions of use for double‐bond location in a variety of substituted or unsubstituted monoolefins.
Mass spectra of t‐butyloxycarbonyl (BOC)‐protected peptides
Authors: Vairamani M. , Srinivas R. , Rao G. K. Viswanadha , Nagaraj R. , Reddy G. Laxma , Saberwal G.
Published: May 2005

Analytically useful mass spectra of t‐butyloxycarbonyl protected tetra‐ and pentapeptides can be obtained under chemical ionization conditions at a source temperature of 250‐270 °C without the use of a reagent gas. The mass spectrum of die thermally labile amino acid arginine could also be recorded under the same conditions.
Hydroxylation of selected hydrocarbon ions on reaction with methanol in the gas phase
Authors: Dolnikowski Gregory G. , Allison John , Watson J. Throck
Published: May 2005

The ion‐molecule reactions of selected hydrocarbon cations with methanol which lead to the production of hydroxylated odd‐electron molecular ions in the high‐pressure ion source of a mass spectrometer or in the central quadrupole of a tandem quadrupole mass spectrometer are described. A wide variety of hydrocarbon cations were investigated, including aliphatic and aromatic cations; of these, only those having a vacant site on an aromatic system appear to undergo the hydroxylation reaction in high yield. A mechanism is proposed for the formation of the molecular ion of phenol from the ion‐molecule reaction involving the phenyl cation with methanol. In addition, thermochemical data are provided which support the formation of the postulated species.
Influence of collision gas on doubly charged ion mass spectra
Authors: Regalado J. R. , Holbrook W. M. , Bostwick D. B. , Moran T. F.
Published: May 2005

The influence of the collision gas on doubly charged ion mass spectra of a selected number of hydrocarbons has been examined. Relative abundances of various product ions in 2E spectra, resulting from charge exchange collisions of doubly charged hydrocarbon ions, do not vary drastically as the collision gas is varied. However, the absolute intensities of these doubly charged ion mass spectra increase significantly when the collision gas is changed from argon to methane to isobutane. Tbese observations are rationalized in terms of a multichannel diabatic curve crossing model.
Tuning and calibration in thermospray liquid chromatography/mass spectrometry using perfluorinated alkyl acids and their ammonium salts
Authors: Stout Steven J. , daCunha Adrian R.
Published: May 2005

Of the several approaches used to interface liquid chromatography with mass spectrometry, the thermospray interface has evolved as the most popular and applicable for the analysis of polar and labile organic compounds. Since a separate ion source must be used for thermospray, separate tuning and calibration are required. Unfortunately, current approaches to tuning and calibration suffer from serious shortcomings, most notably rapid contamination of the ion source. Recent reports have shown that this shortcoming can be overcome by using acetic acid‐ammonia cluster ions or trifluoroacetic acid–ammonia cluster ions for tuning and calibration. In the latter approach, the tuning solution could also be used in the negative ion mode of operation but suffers from concentration of most of the ion current in one ion. The use of perfluorinated alkyl acids and their ammonium salts to generate intense high‐mass negative ions for tuning and calibration to m/z 2000 is reported. Additionally, the ammonium salts of the longer chain perfluorinated acids offer an enhanced high‐mass response in the positive ion mode of operation.
Thermospray mass spectrometry of N‐methylcarbamates
Authors: Saar Jacob , Salomon Avraham
Published: May 2005

The thermospray mass spectrometry (TSP/MS) of five N‐methylcarbamates is presented. This is the first time that ions other than [M + H]+ and [M + NH4]+ have been reported using positive TSP/MS. Protonation of ROCONHCH3 yields the [CH3NH2CO]+· ion, with formation of the ion–molecule adduct [ROCONHCH3 · CH3NH2CO]+· through elimination of CO+· from [CH3NH2CO]+·, and the adduct [M + 75]+·, [ROCONHCH3 · OCONH2CH3]+·, is also obtained.
Negative ion liquid secondary ion mass spectrometry of carbamate‐linked oligodeoxynucleosides. II
Authors: Laramée James A. , Arbogast Brian , Stirchak Eugene P. , Weller Dwight D. , Deinzer Max L.
Published: May 2005

Carbamate‐linked Oligodeoxynucleosides, in which the backbone consists of carbamate and N‐methylcarbamate linkages, have been analyzed by negative ion liquid secondary ion mass spectrometry. Bidirectional sequence‐determining fragmentations are postulated to occur from a common radical anion intermediate that is produced by capture of an ionizing electron by the neutral sample molecule. Fragmentation reactions appear to be related to whether a proton or methyl group is present on the amide nitrogen.
Collisionally induced dissociation mass spectrometric studies of perfluorinated 1H‐heptane, tert‐butanol, 2‐butyltetrahydrofuran and isopropyl bromobutyl ether
Authors: Huang Sunkwei , Tuinman Albert
Published: May 2005

High‐energy collision‐activated dissociation in connection with mass‐analyzed ion kinetic energy spectrometry (CAD/MIKES) was employed to probe the structures of some ions generated by methane chemical ionization (CI) and negative ion chemical ionization (NICI) of the title compounds. CAD/MIKES results show that the [M  H]− ion of lH‐perfluorobeptane and the [O(CF2)4Br]− ion of perfluoroisopropylbromobutyl ether are stable. The methane CI of these fluorocarbons also showed that the expulsion of HF molecules appears to be a major driving force for further fragmentations.
Differentiation of diastereoisomeric terpenoid alcohols by electron impact and negative ion chemical ionization associated with collision‐induced dissociation. A fourier transform ion cyclotron resonance study
Authors: Decouzon Michéle , Gal Jean‐François , Geribaldi Serge , Rouillard Michel , Sturla Jean‐Michel
Published: May 2005

Electron impact ionization‐collision‐induced dissociation (EI‐CID) and negative ion chemical ionization‐collision‐induced dissociation (NICI‐CID) experiments have been performed on the molecular or quasi‐molecular ions (M+· or [M ‐ H]−) of series of terpenoid alcohols, using a Fourier transform ion cyclotron resonance spectrometer. These terpenes belong to the p‐menthane family and bear a hydroxyl group in various positions relative to the isopropyl or isopropenyl substituent (positional or stereochemical isomers). In the case of positional isomers, different CID spectra were always obtained. Within a given diastereoisomeric series, stereochemical differences were also observed in both NICI‐CID and EI‐CID experiments.
Application of dicyandiamide as a matrix additive in fast atom bombardment mass spectrometry
Authors: Caldwell G. W. , Reitz A. B. , Masucci J. A.
Published: May 2005

Dicyandiamide (DCDA) is used as a chemical additive in the fast atom bombardment (FAB) matrix 3‐mercaptopropane‐l,2‐diol (thioglycerol) and propane‐l,2,3‐triol (glycerol). It is demonstrated that DCDA can be used to generate adduct ions [M + H + DCDA]+ for a variety of common organic functional groups to confirm the molecular ion [M + H]+. It is particularly useful for aromatic and alkyl amines and these compounds were therefore investigated in greater detail. Primary and secondary amines on heating react with DCDA to produce biguanides. DCDA can be used as a derivatizing reagent, but the reaction times are typically longer than 12 h and, therefore, it has limited utility. Biguanides can be detected at the nanogram level in full‐range FAB mass spectral analysis.
Spontaneous fragmentations of protonated benzaldimines mediated by intermediate ion‐neutral complexes
Authors: Grützmacher Hans‐Friedrich , Zalfen Ursula
Published: May 2005

4‐Methoxymethylbenzaldimmonium ions (a) and the corresponding N‐methylated ions (b) and N,N‐dimethylated ions (c) were easily generated in the ion source by electron impact‐induced dissociation from 1‐(4‐methoxymethylphenyl)ethylamine and its N‐methylated derivatives. The spontaneous fragmentations of metastable ions a‐c and of specifically deuterated derivatives in the second field‐free region of a VG ZAB‐2F mass spectrometer were studied by mass‐analysed ion kinetic energy Spectrometry. The formation of an amino‐p‐quinodimethane radical cation by loss of the methoxy group is observed for all ions. In the case of a and b carrying at least one proton at the immonium group, competing fragmentations are the loss of CH2O and CH3OH, respectively, and the formation of ions CH3OCH2 +, m/z 45, and C7H7 +, m/z 91. Deuterium‐labelling experiments indicated the migration of a proton from the protonated imino group of a and b to the aromatic ring followed by the loss of methanol from the methoxymethyl side‐chain or protolysis of the bond to either side‐chain to form ion‐neutral complexes, in close analogy with the reactions of the corresponding protonated benzaldehydes. The intermediate ion‐neutral complexes dissociate eventually by internal ion‐neutral reactions resulting in the loss of CH2 O and the formation of C7H7 +, respectively.
Location of double‐bond position in tetradecenols without chemical modification by mass spectrometry
Authors: Horiike Michio , Gu Yuan , Hiranio Chisato
Published: May 2005

Twelve positional isomers of tetradecenol were analysed by conventional combined gas chromatography/mass Spectrometry without any chemical derivatization for the elucidation of the double‐bond position. The spectra were interpreted in terms of similarity of mass spectral patterns based on a fuzzy reasoning method, in which the relative abundances of selected predominant fragment ions were chosen as standard parameters and similarity indices were devised. The method was tested with pure alcohols and enabled the double‐bond position to be located with acceptable accuracy.
Experimentally determined and calculated values of the energies required to form doubly charged ions of the bromomethanes CH3Br, CH2Br2 and CHBr3
Authors: Griffiths W. J. , Harris F. M. , Parry D. E. , Reid C. J. , Ballantine J. A.
Published: May 2005

Two experimental techniques were used to determine the double ionization energies of CH3Br, CH2Br2 and CHBr3. In one, these energies were measured directly by double‐charge‐transfer spectroscopy. In the other, charge stripping of [CH3Br]+, [CH2Br2]+ and [CHBr3]+ ions was investigated and the ionization energies of the singly charged ions were measured. The double ionization energies of the molecules obtained by adding known single ionization energies of the molecules to the single ionization energies of the ions were in good agreement with those determined by double‐charge‐transfer spectroscopy. The relevant mean values from the two techniques were 28.9 ± 0.5, 27.5 ± 0.5 and 29.1 ± 0.5 eV for the double ionization energy of CH3Br, CH2Br2 and CHBr3, respectively. The results of ab initio calculations using second‐order Møller‐Plesset perturbation theory were in good agreement with the observed double ionization energies; they were consistently slightly lower than the experimental values.
Assigning structures to isomeric [C5H10]+ ions: The generation of ionized ethylcyclopropane from pentan‐1‐ol and 1‐chloropentane
Authors: Harnish D. , Holmes J. L. , Lossing F. P. , Mommers A. A. , Maccoll A. , Mruzek M. N.
Published: May 2005

The charge‐stripping mass spectra of the ten C5H10 isomers and of cyclopropane and propene have been re‐evaluated. Oxygen is the preferred collision gas for the former group and helium for the latter pair. A con bined study of the low‐energy mass spectra, charge‐stripping mass spectra and appearance energy measurements had to the conclusion that loss of H2O from ionized pentan‐1‐ol and loss of HCl from ionized 1‐chloropentane both predominantly produce ionized ethylcyclopropane as the fragment ion. For the alcohol, a 1,4‐elimination followed by an energetically favoured 1,2‐H shift is involved, whereas for the halide a direct 1,3‐elimination obtains.
Determination of the isomeric composition of an ionic mixture using collision cross‐sections
Authors: Yoon Bo Un , Kim Myung Soo
Published: May 2005

A theory has been developed for the determination of the isomeric composition of an ionic mixture. The probability theory describing the collisionally activated decomposition (CAD) which was developed previously provided a general foundation for the present theory. Quantification was based on the cross‐sections for the collisional production of daughter ions as observed in the mass‐analysed ion kinetic energy Spectrometry (MIKES). Experimental details for the implementation of the theory have also been developed. The method has been applied to the case of C2H4O+· generated from butane‐l,3‐diol, which is known to be a mixture of more than one isomeric structure. The results seem to be far superior to those based on previous methods, as evidenced by the excellent internal consistency.
Matrix effects on the fast atom bombardment mass spectra of palladium complexes
Authors: Mallis Larry M. , Scott William J.
Published: May 2005

In an attempt to identify and characterize the intermediates involved in multi‐step palladium catalyzed coupling reactions, under fast atom bombardment (FAB) conditions, the selection of a matrix to enhance ion formation without degrading the palladium complex is critical. In general, it is observed that the analysis of tetrakis(triphenylphosphine)palladiurn(0) using glycerol, m‐nitrobenzyl alcohol or o‐nitrophenyl octyl ether as the FAB matrix compound produces several ions which correspond to complexes of the type PdxLyOz+ (L = PPh3; x = 1‐4; y = 1‐4; z = 0‐2), in addition to clusters containing one or more matrix molecules. FAB mass spectra generated using triethanolamine‐ or tetramethylene sulfone (sulfolane) are observed to contain ions related to the palladium(0) complex with little or no interference from ions related to the oxidation or reduction processes.
Metastable ion study of organosilicon compounds. Part III—trimethoxyphenylsilane
Authors: Tajima Susumu , Iida Hiroyuki , Tobita Seiji , Okada Fumio , Tabei Eiichi , Mori Shigeru
Published: May 2005

The unimolecular decomposition of trimethoxyphenylsilane (1) was investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry, deuterium‐labelling studies and from high resolution data. The characteristic fragmentations of metastable molecular ion of 1 were losses of C6H6 and C7H7· with rearrangements. Almost complete H/D scrambling occurred in the molecular ion prior to these decompositions. The other important fragmentation routes corresponded to expulsions of CH3O· and C6H5·. These fragmentations were followed by consecutive elimination of an H2CO molecule, as commonly observed in the mass spectra of alkoxysilanes. In these fragmentation processes, H/D scrambling increased as the internal energy of the molecular ion was lowered. The fragmentations of 1 were compared with those of its carbon analogue, α,α,α‐trimethoxytoluene.
Charge‐Reversal mass spectra of enolate ions of some open‐chain and cyclic ketones for structure identification
Authors: Sürig Thomas , Grützmacher Hans‐Friedrich
Published: May 2005

The charge‐reversal (CR) mass spectra of the enolate ions of heptanal and ten isomeric heptanones, of cyclohexanone, of cycloheptanone, of isomeric methylcyclohexanones, of isomeric ethylcyclohexanones and of the iso meric monoterpene ketones camphor, fenchone, pulegone and thujone were obtained by deprotonation using OH− under chemical ionization conditions followed by collision of the [M − H] − ions with helium in the second field‐free region of a VG ZAB 2F mass spectrometer. The CR mass spectra were evaluated by similarity index (SI) values. Characteristic of the CR mass spectra of the open‐chain enolates are fragment ions formed by α‐cleavage. However, the CR mass spectra are dominated by peaks of small hydrocarbon ions, particularly in the case of cyclic and bicyclic enolates. The CR mass spectra of enolates of linear heptanones differing in the position of the carbonyl group can be easily correlated with the structure of the parent ketone. The CR mass spectra of enolates of isomeric heptan‐2‐ones differing only in the degree of branching of the alkyl group are similar, but can be distinguished by the SI values. The CR mass spectra of the enolates of the isomeric cyclic and bicyclic ketones studied are more or less identical and cannot be used for structural assignment.
Benzene as a selective chemical ionization reagent gas
Authors: Allgood Charles , Lin Yi , Ma Yee‐Chung , Munson Burnaby
Published: May 2005

Dilute mixtures of C6H6 or C6D6 in He provide abundant [C6H6]+· or [C6D6]+· ions and small amounts of [C6H7]+ or [C6D7]+ ions as chemical ionization (CI) reagent ions. The C6H6 or C6D6 CI spectra of alkylbenzenes and alkylanilines contain predominantly M+· ions from reactions of [C6H6]+· or [C6D6]+· and small amounts of MH+ or MD+ ions from reactions of [C6H7]+ or [C6D7]+. Benzene CI spectra of aliphatic amines contain M+·, fragment ions and sample‐size‐dependent MH+ ions from sample ion‐sample molecules reactions. The C6D6 CI spectra of substituted pyridines contain M+· and MD+ ions in different ratios depending on the substituent (which alters the ionization energy of the substituted pyridine), as well as sample‐size‐dependent MH+ ions from sample ion‐sample molecule reactions. Two mechanisms are observed for the formation of MD+ ions: proton transfer from [C6D6]+· or charge transfer from [C6D6]+· to give M+·, followed by deuteron transfer from C6D6 to M+·. The mechanisms of reactions were established by ion cyclotron resonance (ICR) experiments. Proton transfer from [C6H6]+· or [C6D6]+· is rapid only for compounds for which proton transfer is exothermic and charge transfer is endothermic. For compounds for which both charge transfer and proton transfer are exothermic, charge transfer is the almost exclusive reaction.
Mass spectra of heterocyclic compounds VI. 3,4‐dihydro‐1H‐2,3‐benzothiazine 2,2‐dioxides
Authors: Zinczuk Juan , Bravo Rodolfo D. , Orazi Orfeo O. , Corral Renée A.
Published: May 2005

The mass fragmentation behaviour of 3,4‐dihydro‐1H‐2,3‐benzothiazine 2,2‐dioxides was studied. The rationalizations suggested are supported by accurate mass measurements, metastable evidence and deuterium labelling.
Stable γ‐distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction
Authors: Milliet Arielle , Sozzi Georges
Published: May 2005

The γ‐distonic radical ions R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}CHR′CH2ĊHR″ and their molecular ion counterparts R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{{\rm + } \cdot } $\end{document}CHR′CH2CH2R″ have been studied by isotopic labelling and collision‐induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊHCH3, C2H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊHCH3, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊH2, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH2CH2ĊHCH3 and C2H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH2CH2ĊHCH3, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ‐distonic ions, the 1,4‐H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.
Intermediate ion structures in the fragmentation of metastable 3‐methylbutan‐2‐ol radical cations
Authors: George M. , Holmes John L.
Published: May 2005

Ionized 3‐methylbutan‐2‐ol displays four low‐energy fragmentations, loss of CH3· and C3H7· and loss of CH4 and C3H8, the latter pair being produced by metastable ion decompositions. The electron‐impact, metastable‐ion and collision‐induced dissociation mass spectra of 13C and 2H‐labelled isotopomers have been recorded, together with appearance energy measurements. It was found that the fast (ion source) losses of CH3· and C3H7· involved only simple bond cleavages between C(1) and C(2) and between C(2) and C(3), respectively, and without any positional interchange of isotopes. The loss of C3H8 produces ionized vinyl alcohol containing only C(l) and C(2). The H atoms involved are only those attached to C(1) and C(3). In deuterium‐labelled analogues, the deuterium is preferentially located in the propane, e.g. metastable CD3CH(OH)CH(CH3)2 yields predominantly C3H6D2. On the basis of all the observations, it is proposed that low‐energy molecular ions can form a stable proton‐bridged molecule‐radical complex, , and that this key intermediate is responsible for the isotope distribution in propane loss and also for the relatively low importance of the lowest energy dissociation, the simple C(1)C(2) bond cleavage.
New rules concerning the formation of protonated amino acids from protonated dipeptides using the proton affinity order determined from collisionally activated decomposition spectra
Authors: Isa Kimio , Omote Toshiko , Amaya Mitsutaka
Published: May 2005

The use of the order of the proton affinities of natural α‐amino acids for the explanation of the sequence of dipeptidcs using the collisionally activated decomposition mass spectra of protonated dipeptides ions is discussed. New rules are given concerning the formation of protonated amino acid ions from protonated dipeptide ions using the proton affinity order determined by means of fast atom bombardment tandem mass spectrometry for Gly * M2, M1 * Gly, Leu * M2, and M, * Leu systems, where M1 and M2 are the N‐terminal and C‐terminal sides of the dipeptide, respectively.
Fast atom bombardment mass spectra of stibonium salts
Authors: Yu Lu , Fu Gui‐xiang , Liao Yi , Xu Chao‐Wei , Huang Yao‐Zeng
Published: May 2005

The positive‐ion fast atom bombardment (FAB) mass spectra of stibonium salts have been studied. The spectra exhibit an abundant intact cation (C+) and fragment ions resulting from the loss of R, R′ or stable neutral species from the cation. The principal fragment ions in the FAB mass spectra of stibonium salts are [R3Sb]+·, [R2Sb]+, [R2SbH2]+, [RSbR′]+, [RSbH]+, [RSb − H]+ and [R2SbR']+·. In most cases, [ M + C] + cluster ions were detected. When the anion was bromine, the adduct ions [M + (R − H)Sb]+, [C + (R‐H)]+ and [ C + (R′ − H)]+ were also observed, whereas when the anion was [BPh4]−, interesting cluster ions such as [M + (BR′ ‐ H)]+ and [M + (BR′ − 3H)]+ appeared.
Chemical ionization mass spectrometry of bifunctional compounds. The behaviour of bifunctional compounds on protonation
Authors: Nakata Hisao , Suzuki Yumi , Shibata Miyuki , Takahashi Konomi , Konishi Hideyuki , Takeda Naohito , Tatematsu Akira
Published: May 2005

Positive‐ion chemical ionization mass spectra were measured for simple bifunctional aromatic compounds of the type p‐XCH2C6H4CH2Y, where X = NH2, NH(CH3) and N(CH3)2 and Y = OH and OCH3. For each compound, essentially only three peaks of ions, [MH]+, [ MH ‐ XH] + and [MH ‐ YH] +, appeared. The B/E con stant linked‐scan spectra showed that the stable non‐decomposing [MH]+ had the proton only on the nitrogen‐containing functional group. From these data, the relative amounts of total protonation, the ratio of N‐and O‐protonation and the fraction of fragmenting [MH]+ can be calculated. The ease of protonation (protonation susceptibility) and the reactivity (fragmentation capability) of the respective functional groups are discussed.
Evidence for ion‐neutral complex‐mediated reactions well above the threshold for dissociation of the complex
Authors: McAdoo David J. , Hudson Charles E.
Published: May 2005

The possibility that ion‐neutral complex‐mediated eliminations occur well above the threshold for simple dissociation of the partners in the complex was explored. This was accomplished by determining whether daughter ions of probable complex‐mediated dissociations undergo metastable decompositions. All six complex‐mediated decompositions examined formed metastable ions. Therefore, a very small fraction of ion‐neutral complex‐mediated fragmentations may occur several hundred k J mol−1 above the threshold for dissociation of the partners.
Mass spectra of some α‐substituted phenyl‐α,α′‐dimethoxyl ketones and their derivatives
Authors: Chen Guoqiang , Zhang Pang
Published: May 2005

The mass spectra of some α‐substituted phenyl‐α,α′‐dimethoxyl ketones (compounds 1) and their 2,4‐dinitrophenylhydrazones (compounds 2) and semicarbazones (compounds 3) have been studied. The characteristic fragments at m/z (M − 73) from compounds 1, m/z (M − 253) from compounds 2 and m/z (M − 130) from compounds 3 are abundant and proposed to be [ArCROCH3]+. Fragmentations yielding [M+ − 49] from compounds 2 are abnormal and probably involve the methoxyl and nitro groups. The intense peak at m/z 130 due to [CH3OCH2CNNHCONH2]+ from compounds 3 corresponds to α‐cleavage of the molecular ion. Some other fragments from these new compounds are interpreted in this paper.
Determination and enhancement of stereospecific decompositions via triple mass spectrometry: Formation of untypical protonated precursor molecules
Authors: Cole Richard B. , Tabet Jean‐Claude
Published: May 2005

A tetraquadrupole mass spectrometer with consecutive surface‐induced dissociation/collisionally activated dissociation (SID/CAD) capability has been used to investigate the decompositional behaviour of bifunctional terpenes. SID and CAD yield similar daughter‐ion spectra of protonated molecules generated by ammonia chemical ionization. These collision mass spectra of MH+ contain diagnostic daughter ions which can be used to distinguish diastereomeric terpenols. Pronounced stereochemical effects underlying specific decompositions of the ammonium adduct and protonated molecule forms of the bifunctional terpenes have been attributed to the formation of protonated molecules of lower stability produced via decomposition of [M + NH4]+. Evidence supporting the existence of such unusual protonated molecules formed via collision is given in the grand‐daughter spectra of [M + NH4]+. Triple mass Spectrometry is shown to promote the Stereospecific formation and subsequent diagnostic decomposition of these singular protonated forms, thus improving the ability to differentiate the diastereomers.
A combined theoretical and experimental approach to the unimolecular loss of molecular hydrogen from protonated formaldehyde: Determination of the average internal energy of metastable [CH2OH]+ ions
Authors: Hvistendahl Georg , Uggerud Einar
Published: May 2005

Ab initio quantum chemical calculations (MP2/4–31G**) were performed for the dihydrogen elimination reaction from protonated formaldehyde. The energy difference between reactants and products and the activation energies were found to be in good agreement with the corresponding experimental quantities. Theoretical rate vs. energy curves were computed for a series of isotopic variants of the reaction using the Rice–Ramsperger–Kassel–Marcus (RRKM) method. The vibrational frequencies used in these calculations were taken from the 4–31G** geometry‐optimized transition state and reactant structures. Quantum mechanical tunnelling was introduced to explain the existence of metastable CH2OH ions, and a negative kinetic shift of about 0.1 eV was found. The intramolecular kinetic isotope effect for loss of HH/HD and DH/DD was calculated and compared with the experimental data. The result is consistent with the assumption that the average internal energy of metastable [CH2OH]+ ions is very close to the critical energy for H2 loss.
Mass spectra of liquid crystals. III—phenylpyrimidine derivatives
Authors: Leclercq P. A. , van den Bogaert H. M.
Published: May 2005

The 70 eV electron impact mass spectra of 34 1‐phenyl‐2,5‐pyrimidine derivatives are presented. Based on the observed mass shifts by the various substituents, the nature of the main fragment ions is rationalized.
Production of metal atoms, clusters and complexes in pulsed discharge‐excited jets : Studies via mass‐resolved laser multiphoton ionization
Authors: Buntine Mark A. , McGilvery Don C. , Morrison Richard J. S.
Published: May 2005

A pulsed, high‐voltage, discharge‐excited nozzle source has been developed and exploited to study the possibility of sputtering and entraining various metal atoms into the gas expansion from the discharge electrodes. By appropriate choice of electrode materials, atomic beams of copper, silver, tin and lead have been generated and spectroscopically characterized by 2 + 1 laser multiphoton ionization with mass analysis. Sufficiently high atomic densities are achieved with this nozzle system that metal clustering also takes place, producing dimers such as Ag2, species of mixed composition such as AgSn and trimers, Ag3. In addition, chemical reactions have been observed which can be initiated in the discharge and which lead to the formation of metal–ligand complexes when suitable molecules are seeded into the carrier gas. Mass spectral evidence for two such silver complexes is presented.
Repeller‐Induced dissociation of alkyl alcohols in thermospray mass spectrometry
Authors: Saar Jacob , Haimberg Marcela , Chenier Claude
Published: May 2005

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 + NH4]+, above that potential [M + H]+ and fragment ions appeared. The fragments observed were largely due to hydrogen release from alkyl ions ([CnH2n+1]+ – H2 → [CnH2n‐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.
Linear dependence of the intensity of the [M + H]+ ion peak in fast atom bombardment mass spectrometry on the basicity of meso‐substituted octaethylporphyrins
Authors: Van Lin , Fang Yi‐Wei , Liang Xi‐Yun , Wu Guo‐Zhang , Leung Hiu‐Kwong
Published: May 2005

A fast atom bombardment mass spectrometric study of the meso‐substituent effect of Octaethylporphyrins (OEPX, X = NH2, CH3, H, CHO, Cl, CN, NO2) is reported. The intensity of the [M + H]+ ion peaks was estimated quantitatively using an external standard, which was observed to be correlated linearly with the basicity (pK3) of the OEPX. The pK3 value of the OEPXs was obtained by titration with perchloric acid and it was observed to be correlated linearly with Hammett's σp value, with a ρ value of 1.38.