bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron impact ionization of H2O ice
Authors: Safvan C. P. , Raheja U. T. , Mathur D. 
Published: May 2005

AbstractElectron impact ionization and dissociative ionization of water in vapour and ice form has been studied using a newly developed apparatus comprising a well‐collimated beam of 700 eV electrons, a cryogenic target assembly and a quadrupole mass spectrometer. The target assembly consists of a liquid‐nitrogen cooled nickel foil upon which a thin layer of ice is formed. Comparison of the vapour‐phase mass spectrum with that obtained in the ice phase reveals significant differences in the dissociative ionization pattern which are of significance in modelling studies of cold astrophysical environments.
Doubly charged ions: Differentiation of flavanone and 2′‐hydroxy chalcone
Authors: Vékey Károly , Szabó Pál , Dinya Zoltán 
Published: May 2005

AbstractThe metastable and collision‐induced decompositions of the singly charged molecular ions of flavanone and of 2′‐hydroxy chalcone were obtained using mass‐analysed ion kinetic energy spectrometry. Using the same method, neutral losses from, and charge separation reactions of, the doubly charged molecular ions were also determined. The fragmentation characteristics of the doubly and singly charged ions were found to be completely different. Comparison of the spectra of the isomers indicated that both the reactive and unreactive singly charged molecular ions lose their structural identity by the time they reach the second field‐free region; flavanone ions probably isomerize to 2′‐hydroxy chalcone ions. The corresponding doubly charged molecular ions, on the other hand, do not isomerize, and their spectra are quite distinct. This result suggests that spectra of doubly charged ions may, in some cases, be more suitable for the characterization of isomers than singly charged ions.
Ion trap and quadrupole mass spectra of lignin pyrolysates: How well do they compare?
Authors: Galletti Guido C. , Reeves James B. , Francis Barry A. , Reeves Valerie B. 
Published: May 2005

AbstractLignin samples from wheat straw, orchard grass, red clover and a synthetic lignin were subjected to pyrolysis gas chromatography/mass spectrometry using both quadrupole (QMS) and ion‐trap detector (ITD). ITD mass spectra were comparable with those presented in the National Bureau of Standards (NBS) library and with those obtained by QMS as evaluated by discrepancy factors. Computer‐assisted library searches for ITD spectra were successful for 22 of 47 compounds. The other 25 compounds were not present in the library. A typical program and mass spectra are shown. Statistical data are discussed.
Fast‐atom bombardment mass spectrometric study of some N‐ and S‐glycosides of acetylated hexose isomers
Authors: Liptáak Miklós , Heerma Wigger 
Published: May 2005

AbstractVarious N‐aryl, S‐aryl and S‐alkyl glycosides of acetylated D‐glucose, D‐galactose and D‐mannose have been studied by fast‐atom bombardment mass spectrometry. It was found that the matrix used has a considerable effect on the relative peak intensities in the molecular mass region. Glycerol apparently promotes the formation of protonated molecules (MH+) whereas in 3‐nitrobenzyl alcohol both MH+ ions and M+· radical cations are abundant. The unimolecular decomposition spectra of the MH+ ions exhibit two significant peaks corresponding to losses of acetic acid and of the aglycon. The intensity ratios of these fragment ions are dependent on the nature of the aglycon and the hexose unit and can be used to identify the monosaccharides. It has also been established that acetic acid elimination occurs mainly from the C‐3 position.
Time‐base modulation for the correction of cyclotron frequency shifts observed in long‐lived transients from fourier‐transform ion‐cyclotron‐resonance mass spectrometry of electrosprayed biopolymers
Authors: Bruce James E. , Anderson Gordon A. , Hofstadler Steven A. , Winger Brian E. , Smith Richard D. 
Published: May 2005

AbstractThe occurrence of small shifts in the cyclotron frequency during the acquisition of very long transients (in excess of 80 s) has been observed to be a limiting factor for ultrahigh‐resolution mass measurements of protein ions performed with electrospray‐ionization Fourier‐transform ion‐cyclotron‐resonance mass spectrometry. Resolution measurements were restricted to values less than 106 because of the frequency shifts. Measurements of the frequency shifts, performed by sequentially transforming small segments of the transient, allowed the shift to be characterized and fitted to a 4th‐order equation. The sampling rate of the acquired transient was then modulated (at a rate equal to the reciprocal of the rate for the frequency shift) to allow ultrahigh resolution, greater than 2 × 106, and improved mass measurement and precision to be achieved for a small protein.
Reactions of low‐energy ions with ferrocene self‐assembled monolayer surfaces
Authors: Pradeep T. , Riederer D. E. , Ast T. , Cooks R. G. 
Published: May 2005

AbstractCollisions of low‐energy Cr(CO) (n = 0, 2, 6) ions with self‐assembled monolayer surfaces bearing covalently bound ferrocene groups result in transfer of the cyclopentadienyl ligand into the gas phase as the Cr(C5H5)+ ion. High fluences of Cr+ ions lead to deposition of Cr at the surface and subsequent Xe+ collisions liberate the metal ion. The Cr atoms deposited on the surface appear to be chemically bonded to the cyclopentadienyl rings. The implications of these results for modification of surfaces using ion beams are discussed.
Multiple excitation collisional activation in Fourier‐transform mass spectrometry
Authors: Lee Samuel A. , Jiao Charles Q. , Huang Yongqing , Freiser Ben S. 
Published: May 2005

AbstractMultiple excitation collisional activation (MECA) has been examined using Fourier‐transform mass spectrometry. In analogy to recently reported multiple excitation detection schemes, MECA is a process in which ions are translationally excited to larger orbits by applying an RF signal over the desired mass range. Next, collisional cooling of the ions collapses them, spatially, back to the center of the cell, where the process can be repeated. Two examples of the utility of MECA are given. The first involves a novel way of growing cluster ions by sequential ion/molecule reactions followed by MECA. The second uses MECA to increase the energy deposition in a stable and difficult‐to‐fragment ion, thereby inducing fragmentation.
Bond activation by d0 metal carbene complexes in the gas phase
Authors: Wilson Kimber L. , Cooper Brian T. , Buckner Steven W. 
Published: May 2005

AbstractThe formation and bond activation reactions of the d0 carbene complexes MCHCN+ (M = Sc, Y) are presented. Sc+ and Y+ dehydrogenate acetonitrile to produce the metallocarbenes. The carbene complexes are less reactive towards hydrocarbons than their bare metal ion counterparts, but will activate CH, OH, and NH bonds through a four‐centered intermediate. Labeling studies indicate that reactions with olefins proceed by migratory insertion after initial CH activation, and that subsequent ligand coupling produces metal‐bound nitrite products. Oletin metathesis reactions are not observed due to the electron‐withdrawing characteristics of the CN substituent and the electrophilicity of the metal centers.
Metastable ion study of organosilicon compounds, part VII.1 Losses of C2H4 and CH4 from the metastable dimethylsilyl ion [(CH3)2Si+H]
Authors: Tabei Eiichi , Mori Shigeru , Kinoshita Takeshi , Kawazoe Kayoko , Tajima Susumu 
Published: May 2005

AbstractThe spontaneous unimolecular dissociative reactions of dimethylsilyl cations (CH3)2Si+H (1+; m/z 59) have been investigated by mass‐analyzed ion kinetic energy (MIKE) spectrometry and deuterium‐labelling studies. Excepting the losses of H and H2, the ions 1+ mainly eliminate C2H4 and CH4 to produce product ions at m/z 31 and 43, respectively. Almost complete hydrogen scrambling occurs prior to the C2H4 loss, but only a small degree of scrambling occurs in the CH4 loss. Predominantly, the hydrogen atom bound to Si participates in the latter reaction, contrary to the previously reported mechanism.
Mass spectra of some phenylphosphinosilanes
Authors: Kim Tae Wook , Jahng Woong Sang , Kim Chang Hwan , Lee Myong Euy 
Published: May 2005

AbstractThe 70 eV electron‐impact low resolution spectra of Me3SiPPh2, (Me3Si)3SiPPh2, and (Me3Si)2(Me)SiP(Me)(Ph) were investigated. The migration of two phenyl groups from phosphorous to a silicon site was observed and the unimolecular mass‐analysed ion kinetic energy spectra indicated that the migration occurred in [M  CH3]+ ions rather than in M+· ions. The benzene eliminations from the M+· and [M  CH3]+ ions of Me3SiPPh2 were observed not in the EI spectrum, but in their MIKE spectra.
Mass spectrometric sequencing of linear peptides by product‐ion analysis in a reflectron time‐of‐flight mass spectrometer using matrix‐assisted laser desorption ionization
Authors: Kaufmann R. , Spengler B. , Lützenkirchen F. 
Published: May 2005

AbstractIn matrix‐assisted laser desorption ionization (MALDI) a large fraction of analyte ions undergo post‐source decay (PSD) during flight in the field‐free drift path. By means of a modified two‐stage reflectron, product ion time‐of‐flight spectra of medium‐sized linear peptides (up to 2800 u) were recorded, containing full sequence information. Precision, accuracy and mass resolution of fragment ions were almost as good as obtained in high‐energy collisionally activated dissociation (CAD) studies performed in four‐sector instruments. Instrumental sensitivity was better by at least one order of magnitude. In reflectron time‐of‐flight mass spectrometry (RETOF‐MS) the cleavage pattern of PSD products is different from that obtained by high‐energy and low‐energy CAD. Activation mechanisms of PSD were found to be largely determined by collisional events (ion/neutral) occurring in the acceleration field during early plume expansion. Future potentials of PSD analysis after MALDI are discussed.
Selected‐ion accumulation from an external electrospray ionization source with a fourier‐transform ion cyclotron resonance mass spectrometer
Authors: Bruce James E. , Anderson Gordon A. , Hofstadler Steven A. , van Orden Steven L. , Sherman Michael S. , Rockwood Alan L. , Smith Richard D. 
Published: May 2005

AbstractThe coupling of an electrospray ionization (ESI) source to a Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometer provides a facility for the high resolution, accurate mass analysis of large biopolymers. Typically the m/z range of the electrosprayed ions injected and trapped in the FTICR cell is between m/z 500 and 2500 (but can vary considerably with solution conditions). Recent reports on quadrupole excitation have demonstrated the ability to cool the magnetron motion of ions trapped in the FTICR mass spectrometer cell by converting this motion to cyclotron motion which, under appropriate pressure conditions, damps readily to the center of the cell. The use of a broadband waveform (swept frequency or stored waveform inverse Fourier‐transform) for the quadrupole cooling pulse was shown to provide cooling of a wide range of m/z ions, while implementation of a single frequency demonstrated a much narrower m/z response. This report demonstrates the successful combination of single‐frequency quadrupole cooling with external injection of electrosprayed ions into an FTICR mass spectrometer for m/z selected‐ion accumulation. This capability is particularly significant with electrospray ionization since it allows ions of only one charge state to be accumulated in the cell, and greatly increases the potential dynamic range of ESI‐FTICR.
Jet separator/membrane introduction mass spectometry for on‐line quantitation of volatile organic compounds in aqueous solutions
Authors: Dejarme L. E. , Bauer S. J. , Cooks R. G. , Lauritsen F. R. , Kotiaho T. , Graf T. 
Published: May 2005

AbstractA new technique is described for the direct detection of volatile organic compounds present in aqueous solutions at levels in the parts per trillion range. The sample is enriched in analyte in two consecutive stages; one utilizes a semi‐permeable membrane interface and the other a jet separator. The analyte solution is sampled as it flows coaxially over a semi‐permeable capillary membrane, the interior of which is continuously purged by helium. The permeate is pneumatically transported to the mass spectrometer via a jet separator, which is used to remove excess helium and 'vater from the analyte vapor strean. Data are reported for two instruments; in one the membrane/jet separator system is interfaced to a single ijuadrupolc mass spectrometer via a custom‐built metal jet separator with a variable capillary gap. In the second, an ion‐trap mass spectrometer is used in conjunction with a conventional fixed‐gap quartz jet separator. Typical analyte response times are 2–5 min at ambient temperature, and Mow injection methods are used for sample delivery. Direct comparisons, made under identical instrumental conditions, show that the jet separator system displays even lowsr detection limits than a conventional direct‐insertion membrane probe. Detection limits in the range 30 parlis per trillion to a few parts per billion are observed for selected volatile organic compounds and the response is linear over 3 orders of magnitude.
Analysis of the squalestatins by on‐line packed capillary liquid chromatography combined with electrospray mass spectrometry
Authors: Lane S. J. , Brinded K. A. , Taylor N. L. , Watkins P. J. F. , Harrison M. E. 
Published: May 2005

AbstractA mixture of four squalestatins was separated anil characterized by gradient packed capillary liquid chromatography combined with electrospray collision‐induced dissociation mass spectrometry (ESI/CID/MS). Negative‐ion ESI was found to afford spectra typified by strong pseudo‐molecular ions but providing little structural information. Structural information was obtained using an ion‐focusing RF‐only octapole lens to provide conditions for CID. The new method showed improvements in sensitivity when compared to existing thermospray and dynamic liquid secondary‐ion mass spectrometry methods.
Application of a parallel computer to simulation of ion trajectories in an ion cyclotron resonance spectrometer
Authors: Miluchihin Nickolay V. , Miura Kenji , Inoue Masao 
Published: May 2005

AbstractA parallel computer was used to calculate ion trajectories in the cell of an ion cyclotron resonance spectrometer. Computation was carried out 512 ions simultaneously. Ion‐cloud evolution in a non‐uniform electric field and ion/neutral collision processes were introduced to demonstrate the capability of parallel computation. The performance evaluation of a parallel computer was fulfilled.
Electron affinities of higher fullerenes
Authors: Boltalina O. V. , Sidorov L. N. , Ya. Borshchevsky A. , Sukhanova E. V. , Skokan E. V. 
Published: May 2005

AbstractKnudsen cell mass spectrometry has been used for the investigation of ion‐molecule equilibria between gaseous neutral species and negative ions in fullerenc vapors at 800–900 K. Equilibrium constants of one‐electron exchange reactions between C60 and the higher fullerenes C70, C76, C78 and C84 have been measured. Electron affinities of C70, C76, C78 and C84 were found to be 2.72 ± 0.05, 2.88 ± 0.05, 3.01 ± 0.07, and 3.05 ± 0.08 eV respectively. Negative ions of C86, C90, and C92 were observed, and the lower limit of electron affinities for these species was estimated as ≥3.0eV.
Small volume and low flow‐rate electrospray lonization mass spectrometry of aqueous samples
Authors: Gale David C. , Smith Richard D. 
Published: May 2005

AbstractA new electrospray ionization source (emitter) has been developed which allows the effective utilization of very small sample volumes at much lower flow rates than previously demonstrated. A small diameter etcched‐tip capillary has been incorporated into a pressure‐infusion electrospray ionization source. The ability to electro‐spray aqueous solutions without the use of an ancillary sheath flow is demonstrated with several biopolymers. High signal intensities and stable signals are observed for this source in a comparison with a standard methanol‐sheath source.
A curved‐field reflectron for improved energy focusing of product ions in time‐of‐flight mass spectrometry
Authors: Cornish Timothy J. , Cotter Robert J. 
Published: May 2005

AbstractA new type of curved‐field reflectron has been developed for the energy focusing of ions formed after initial acceleration in time‐of‐flight (TOF) mass spectrometers. These include ions generated in the dissociation region of a tandem TOF, as well as metastable decay products formed in the field‐free drift region prior to their reflection. Unlike conventional linear‐field reflectrons, which focus product ions to different focal lengths that are proportional to the mass (energy) of the fragment, the new curved‐field reflectron energy focuses all ions to within a small region near the exit of the reflectron. Thus, the collection of resolved fragment peaks is possible without scanning or stepping the potential gradient of the reflectron, enabling faster acquisition of the production spectrum and, more importantly, true multiplex recording of the spectra from each ionization event. Theoretical considerations of the design are discussed along with an evaluation of collision‐induced dissociation data, demonstrating the performance of the new reflectron in a tandem TOF instrument.
Facile identification by electrospray mass spectrometry of the insulin fragment A14–21‐B17–30 produced by insulin proteinase
Authors: Vu Lan , Stöcklin Reto , Rose Keith , Offord Robin E. 
Published: May 2005

AbstractWe confirm the cleavage at position B16–17 of porcine insulin which occurs during in vitrio digestion by insulin proteinase. The fragment A14–21‐B17–30 was purified by reversed‐phase high performance liquid chromatography and characterized by electrospray ionization mass spectrometry. Fast‐atom bombardment mass spectrometry, on the other hand, failed todetect the presence of this fragment.
Characterization of succinimide‐type dehydration products of recombinant hirudin variant 1 by electrospray tandem mass spectrometry
Authors: Grossenbacher H. , Märki W. , Coulot M. , Müller D. , Richter W. J. 
Published: May 2005

AbstractTwo congeners Q4 and Q5 inferred in earlier analyses to be cyclic succinimide‐type dehydration product; of recombinant hirudin (variant 1) were structurally fully characterized. After isotopic labeling by ring‐opening with H218O, the suspected anhydro‐positions Asp53 and Asp33 were confirmed by tandem mass spectrometry (MS/MS) sequencing of relevant smaller peplides directly in the enzymatic hydrolysates (V8 protease) using electrospray MS/MS. The chosen strategy proved highly efficient and sensitive.
Direct peptide mapping of sickle‐cell hemoglobin using electrospray mass spectrometry
Authors: Sakairi Minoru 
Published: May 2005

AbstractDirect peptide mapping of sickle‐cell hemoglobin (Hb S) using electrospray mass spectrometry is demonstrated to be a rapid, sensitive and useful technique for providing information concerning the location of variation. By fully comparing electrospray mass spectra of digests of sickle‐cell and normal hemoglobins, using L‐l‐tosylamide‐2‐phenylethyl chloromeihyl ketone (TPCK)‐treated trypsin, the point mutation of B1 fragment of β‐chain in Hb S can be confirmed, taking into consideration that all the other fragments are completely identical in the two proteins.
Identification of double‐bond position in the sex pheromone of china corn borer by mass spectrometry
Authors: Yuan Gu , He Meiyu , He Xiaoran 
Published: May 2005

AbstractThe female sex pheromone of the China corn borer, Ostrinia furnacalis (Lepidoptera: Pyralidae), was confirmed as Δ12‐tetradecenyl acetate by a ‘fuzzy’ similarity analysis of gas chromatograph/mass Spectrometry data.
Mass spectral fragmentation reactions of some stereoisomeric cyclic β‐amino acids under electron and chemical ionization
Authors: Partanen Tuula , Vainiotalo Pirjo , Stájer Géza , Bernáth Gábor , Göndös György , Pihlaja Kalevi 
Published: May 2005

AbstractMass spectral fragmentations of two cyclopentane, four cyclohexane/ene and four norbornane/ene ß‐amino acids were studied under electron ionization by low‐resolution, high‐resolution, metastable ion analysis and collision‐induced dissociation techniques. All stereoisomeric compounds gave rise to identical 70 eV electron‐ionization mass spectra. The major fragmentation pathway for the saturated compounds began as an α‐cleavage reaction with respect to the nitrogen atom. For the unsaturated compounds, a retro‐Diels–Alder reaction was favoured. In addition to a normal retro‐Diels‐Alder fragmentation reaction, the norbornene compounds underwent a retro‐Diels‐Alder fragmentation reaction accompanied by the migration of one hydrogen atom. In the case of the chemical ionization mass spectra, differences between stereoisomers were observed only under methane chemical ionization, where monocyclic trans isomers decomposed more readily than the corresponding cis isomers. All the [M + H]+ ions decomposed mainly by dehydration and deamination reactions. The fragmentation in the chemical‐ionization ion source resulted in the same elimination ratio [M + H  H2O]/{[M + H  H2O] + [M + H  NH3]} as observed under kinetic control in the collision region.
Computer‐Designed waveform technique for reducing chemical noise in atmospheric‐pressure ionization/ion‐trap mass spectrometry
Authors: Mordehai Alex V. , Henion J. D. 
Published: May 2005

AbstractThis paper describes implementation of a storage waveform technique for manipulation of ions in a quadrupole ion trap. The technique is similar to the well established storage waveform inverse Fourier‐transform (SWIFT) technology for controlling ion motion in Fourier‐transform ion cyclotron resonance (FT‐ICR). These techniques allow one to manipulate ions stored in the trap through computer control. The focus of this paper is the application of the storage waveform technique to the chemical noise problems associated with the analytical applications of atmospheric‐pressure ionization/ion‐trap mass spectrometry. In particular, the wave function described results in selected‐ion accumulation in the trap in a mass window of ∼︁ 100 u. The position of the mass window can easily be adjusted across the mass range, thus providing selective accumulation in the trap only for ions of interest, while removing all others. The technique is easily implemented for routine use with on‐line separations, resulting in improved sensitivity by significantly reducing ion current from interfering chemical background.
Mass spectrometric studies on azasqualenes, a class of 2,3‐oxidosqualene cyclase inhibitors
Authors: Ceruti Maurizio , Seraglia Roberta , Traldi Pictro 
Published: May 2005

AbstractThe mass spectrometric behaviour of a series of azasqualenes and azasqualanes has been studied by two different instruments, a double focusing machine and an ion‐trap mass spectrometer (ITMS). The high abundances of fragmentation products obtained using the former indicate that with ITMS, processes additional to electron ionization must be present, leading to molecular species with lower internal energy contents.