bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostatic quadrupole lens simulation in potential array relaxation programs
Authors: Jayaweera Palitha , Ramaley Louis , Boerboom A. J. H.
Published: May 2005

Lens and ion trajectory simulation programs, such as the popular program SIMION, which employ potential array relaxation methods, are very useful in designing and modifying ion lens systems. Unfortunately, these programs cannot simulate lenses of certain geometries such as quadrupoles. Several approaches for portraying static DC quadrupole lenses accurately in such programs have been investigated. These include user programming, an option in the latest version of SIMION, and array modification. The most convenient and accurate method involves modifications to the lens arrays employing relaxation techniques similar to those used in SIMION itself. These have been incorporated into a self‐contained computer program named QREFINE, which is available to interested parties.
Strategy for sequencing peptides as mono‐ and dilithiated adducts using a hybrid tandem mass spectrometer
Authors: Leary Julie A. , Williams Todd D. , Bott Geoffrey
Published: May 2005

A strategy for sequencing peptides using the mono‐ and dilithiated quasimolecular ions is proposed. Low energy collision‐induced dissociation (CID) of the monolithiated species produced primarily [An+LiH]+ and [Bn+H+OLi]+ ions while that of the dilithiated species produced [An+LiH]+ and [Yn+Li+H]+ ions. The precursor parent ion in the monolithiated adduct is proposed to be a mixture of lithiated neutral peptide (1) and protonated lithium salt (2). Mechanisms for the formation of the [An+LiH]+ and [Yn+Li+H]+ ions are proposed. Four peptides of known composition but unknown sequence were successfully sequenced using the combined data from the CID spectra of the mono‐ and dilithiated species.
Comparison of fast‐atom bombardment, thermal ionization and inductively coupled plasma mass spectrometry for the measurement of 64Zn/67Zn stable isotopes in human nutrition studies
Authors: Eagles J. , Fairweather‐Tait S. J. , Mellon F. A. , Portwood D. E. , Self R. , Götz A. , Heumann K. G. , Crews H. M.
Published: May 2005

Fast‐atom bombardment, thermal ionization and inductively coupled plasma mass spectrometry are contrasted in comparative measurements of 64Zn/67Zn isotope ratios on samples isolated in the course of a human mineral‐nutrition experiment. The data are evaluated with reference to the precision normally required in enriched stable‐isotope mineral‐nutrition studies, and the convenience of the mass spectrometric techniques is also compared.
Collisionally activated decomposition spectra of normal nucleosides and nucleotides using a four‐sector tandem mass spectrometer
Authors: Sakurai T. , Matsuo T. , Kusai A. , Nojima K.
Published: May 2005

Collisionally activated decomposition spectra derived from normal nucleosides and nucleotides have been studied using a four‐sector tandem mass spectrometer. The selectivity for a precursor ion has been improved by the use of the first two sectors as a double‐focusing mass spectrometer, and the mass resolution of daughter spectra has been enhanced using the next two sectors as a second double‐focusing mass spectrometer. Reliable and reproducible data with respect to the structure of nucleosides and nucleotides have been obtained.
Do ion trap and quadrupole lead to identical results in the analysis of terpenoic compounds?
Authors: Galletti G. C. , Traldi P. , Bonaga G. , Chapman J. R.
Published: May 2005

The ion trap detector (ITD) is effective in the analysis of terpenoic mixtures from essential oils. ITD spectra are compared in library searches with spectra from a quadrupole mass spectrometer. ITD generally leads to lower FIT values, although its efficiency in terms of structural identification is comparable to that of quadrupolar systems.
Isotope label scrambling in alkyl cations. A mechanistic proposal
Authors: Tuinman A. A. , Cook K. D. , Macfarlane Ronald D.
Published: May 2005

The observation of sharp limits to the chain lengths of alkyl cations derived by low energy collision‐induced dissociation of isotopically labelled trimethyltetradecylammonium cations, as well as the selectively limited scrambling of its isotope label, has prompted the proposal of a new mechanistic model for alkyl cation fragmentation. The model invokes protonated cyclopropane intermediates which may reopen to branched structures, or fragment (if suitably substituted) to form smaller alkyl cations and neutral olefins. The model accounts completely for the absence of daughter ions with fewer than three or more than six carbon atoms, while its semi‐quantitative application provides a reasonable match to the observed isotope scrambling.
Do the benzyl and silabenzyl anions show similar ion chemistry in the gas phase?
Authors: O'Hair Richard A. J. , Bowie John H.
Published: May 2005

The ion PhSiH undergoes a number of fragmentations upon collisional activation, including losses of H˙, H2 (mainly to form PhSi−), and SiH2, together with formation of HSi−. The ion/molecule chemistry of PhSiH is characteristic of silyl anion systems and bears no analogy to that of benzyl anion reactions; for example with N2O and CO2 it forms Ph(H)2SiO− as the sole ionic product, while with CS2 it yields Ph(H)2SiS−.
Cluster‐ion formation between solvent and matrix using fast‐atom bombardment mass spectrometry
Authors: Haskins N. J. , New A. P.
Published: May 2005

Fast‐atom bombardment ionization requires the sample to be in solution. This is often achieved by predissolving the sample in a suitable solvent. However, spectra can be obscured by solvent/matrix cluster ions. This work has examined a number of common solvents and their propensity for clustering with glycerol or other matrices.
Instrument‐independent database for collisionally activated dissociation in radiofrequency‐only quadrupoles. Single‐collision versus multiple‐collision conditions
Authors: Martinez Richard I. , Ganguli B. , Cooks R. G.
Published: May 2005

The collisionally actived dissociation (CAD) of the acetone cation (m/z 58) and of the acetyl cation (m/z 43) from acetone were studied under single‐collision and multiple‐collision conditions. A kinetics‐based measurement protocol developed at the National Institute of Standards and Technology was used to measure the CAD spectra (i.e., the product distributions (branching ratios) of the CAD fragment ions). A protocol is proposed for a second interlaboratory round robin to explore the feasibility (or lack thereof) of measuring standardized, instrument‐independent CAD spectra under multiple‐collision conditions.
A coordinated approach towards the molecular weight determination of peptides by gel electrophoresis and fast‐atom bombardment mass spectrometry
Authors: Camilleri Patrick , Haskins Neville J , Hill Andrew J , New Anthony P , Games D. E.
Published: May 2005

The molecular weight of peptides can be determined by fast‐atom bombardment mass spectrometry (FAB‐MS) following polyacrylamide gel electrophoresis (PAGE). Initial results combining the fast and efficient separation of peptides by PAGE and the unambiguous determination of molecular weights by FAB‐MS have been demonstrated for the three peptides bradykinin, neurotensin and gramicidin S. This method has also been applied to the determination of the molecular weights of two fragments from the tryptic digest of horse‐heart cytochrome c.
Isomer discrimination of polycyclic aromatic hydrocarbons in negative‐ion chemical ionization mass spectrometry using carbon dioxide
Authors: Elson C. M. , Sim P. G.
Published: May 2005

The negative‐ion chemical ionization mass spectra of a group of isomeric polycyclic aromatic hydrocarbons (PAH) have been studied using CO2 as reagent buffer gas. The spectra show reproducible and characteristic differences between members of the set, implying that this technique offers some potential for distinguishing among groups of PAH isomers.
Potential misidentification of trichlorophenylethanol in imported peppers
Authors: Cairns Thomas , Siegmund Emil G. , Barry Thomas L. , Petzinger Glenn
Published: May 2005

During regulatory analyses for the determination of pesticide residues on agricultural commodities, a frequently encountered trichlorinated compound was misidentified by the NBS library search routine. This case history illustrates the need for more rigorous confirmation criteria when dealing with multi‐chlorinated compounds where fragmentation can be dominated by methyl loss followed by loss of CO and HCl.
A terbody complex intermediate in [alkyl ether…︁\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm H}\limits^ + $\end{document}…︁alcohol] ions
Authors: Monteiro C. , Audier H. E. , Mourgues P. , Berthomieu D.
Published: May 2005

Ions of the form [alkyl ether…︁\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm H}\limits^ + $\end{document}…︁alcohol] have been generated in the ion‐source of a VG ZAB 2F mass spectrometer and studied in the 2nd field‐free region. The metastable ions only give the protonated alkyl ether fragment if there is no tertiary carbon in the α position of the oxygen atoms. If there is a tertiary carbon, the formation of protonated ether competes with other processes involving the elongation of the OCα (tertiary) bond(s). With tertiary alcohols and nontertiary ethers, this elongation leads to a terbody complex in which the tertiary carbocation is solvated by the ether and a molecule of water or, if the ether contains one tertiary group, a terbody complex is formed where the tertiary carbocation is solvated by two molecules of alcohol. Furthermore, a permutation between tertiary groups is observed when both ether and initial alcohol bear such substituents. Most probably, the formation of terbody complexes competes with other mechanisms, concerted processes, for instance.
Determination of the charge state of ions in thermospray mass spectra
Authors: Chan K. , Wintergrass D. , Straub K.
Published: May 2005

Analysis of the profiles of isotope clusters can be used to determine the charge state of ions in thermospray mass spectrometry. This observation was verified by comparison of experimental results with theoretical calculations. The applicability of this technique was illustrated by the characterization of peptides whose molecular weights were in the range of 500 to 5000 Da. Using thermospray ionization on a quadrupole mass spectrometer, [M + 2H]2+ and [M + 3H]3+ ions of the peptides were identified. These multiply charged ions enabled us to characterize molecules with molecular weights exceeding the normal mass range of the instrument.
Quadrature heterodyne method for fourier‐transform ion cyclotron resonance mass spectrometry
Authors: Fujiwara Makoto , Katakura Hisao , Inoue Masao
Published: May 2005

In Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectra resulting from the signals detected with a single pair of detection plates (i.e., real‐time‐domain signals), the foldback of spectral information about the Nyquist frequency occurs. In heterodyne mode FT‐ICR mass spectrometry, using quadrature reference signals, a complex ICR signal consisting of two quadrature reference signals, a complex ICR signal consisting of two quadrature signal components can be acquired easily. By Fourier transform of the signal, the reflection of peaks about the Nyquist frequency in the frequency‐domain spectrum can be eliminated. As a result, the available bandwidth of the spectrum is doubled. Validity of this quadrature heterodyne method is confirmed by the experimentally obtained spectrum of Xe+ ions.
Collision‐energy ramp. A modification to an RF‐only quadrupole collision cell
Authors: Bott Geoffrey , Ogden Sherri , Leary Julie A.
Published: May 2005

A modification to the electronics controlling the collision energy of an RF‐only quadrupole collision cell in a BEqQ geometry mass spectrometer is described. The modification allows the collision energy to be ramped from 0–500 eV while scanning the quadrupole mass analyser. The collision‐induced dissociation spectra generated using a ramped collision energy exhibit a 10%–100% increase in product‐ion abundance.
On‐line combination of supercritical‐fluid chromatography with fast‐atom bombardment mass spectrometry
Authors: Matsuura K. , Takeuchi M. , Nojima K. , Kobayashi T. , Saito T.
Published: May 2005

Studies on combined supercritical‐fluid chromatography (SFC) using a packed column, with fast‐atom bombardment mass spectrometry (FAB‐MS) are described. The interfacing was successfully carried out by simply coupling a frit interface between the liquid chromatograph (LC) and the mass spectrometer. The interface was equipped with a pneumatic splitter and post‐column addition device delivering FAB matrix material to a release valve which maintained a constant back‐pressure at the column outlet. Using a 1% glycerol solution as a matrix compound in the release valve, the SFC/FAB‐MS combination operates as well as a normal LC/MS instrument. The performance was demonstrated with a mixture of α‐, β‐ and γ‐tocopherol and Triton X‐100 (poly(ethylene glycol) p‐isooctylphenyl ether).
Reproducing daughter‐ion spectra using the transmission oscillation properties of quadrupole collision cells
Authors: Lamb John H. , Naylor Stephen
Published: May 2005

The transmission oscillation properties of parent ions through an RF‐only quadrupole are investigated as a function of collision energy, radicfrequency of the quadrupole, and type and pressure of target gas. It is shown that small variations of collision energy can result in substantial differences in daughter‐ion spectra obtained from the same parent ion. Since absolute values of collision energy are difficult to determine, reproducible daughter‐ion spectra are problematical to acquire.

In this work we show that reproduction of daughter‐ion spectra, using the transmission properties of the collision cell, is possible. The characteristics of an RF‐only quadrupole (Q*) are such that the parent ion intensity at the second detector varies as a function of collision energy and displays sinusoidal properties. By using the nodes and anti‐nodes of the parent‐ion transmission it is possible to achieve reproducible daughter‐ion spectra of a wide range of biopolymers. The tuning of Q* is mass‐dependent and not compound‐dependent. Hence it is possible to optimize and tune Q* using an isobaric (or almost) standard such as one of the ions of perfluorotri‐n‐butylamine (electron ionization) or a glycerol cluster ion (fast‐atom bombardment mass spectrometry) before subjecting valuable sample to tandem mass spectrometry.
Experience in the use of a 4‐sector instrument and array detector and its application in peptide analysis
Authors: Burlingame A. L. , Walls F. C. , Falick A. , Evans S. , Riddoch A. , Buchanan R.
Published: May 2005

A 4‐sector EBEB mass spectrometer, fitted with a liquid secondary‐ion mass spectrometer (Cs+) ion source and an array detector has been in use at UCSF for the past 18 months. Using this period, calibration procedures have been developed and operating software refined such that the instrument can now be operated in the tandem mass spectrometry (MS/MS) mode using the array on a routine basis and with a high sample throughput. The instrument has been applied successfully to the analysis of a wide range of peptides, up to molecular weights in excess of 2500. The array is usually operated with a mass resolution of about 1500 full width at half maximum (FWHM), and under these conditions a fragment ion dynamic range of 3000:1 is obtainable. Mass assignment is typically reproducible to within 0.1 u.
Electron‐ionization‐Induced fragmentation of N‐monosubstituted 2‐phenylacetamides
Authors: Jeremić Ljiljana A. , Kobilarov Nestor L. , Petrović Slobodan D.
Published: May 2005

Electron‐ionization‐induced mass spectra of N‐monosubstituted 2‐phenylacetamides were recorded and their fragmentation patterns were studied by metastable‐ion analyses. Representative deuterated analogues of these compounds have also been synthesized and their mass spectra compared with those of the unlabelled parent compounds. The most typical fragmentation for N‐alkyl‐, N‐isoalkyl‐ and N‐cycloalkyl‐2‐phenylacetamides is cleavage of the bond β to the carbonyl function, resulting in an ion fragment of m/z 92, following the transfer of hydrogen and elimination of a corresponding ketene. The primary fragmentation process for N‐aryl substituted 2‐phenylacetamides is the loss of an aromatic hydrogen atom from the molecular ion. The other principal fragmentation processes observed with these compounds are discussed.
Accurate mass measurement of positive ions produced by ammonia chemical ionization
Authors: Lawrence David L.
Published: May 2005

A technique is described which enables the accurate mass measurement of positive ions produced under ammonia chemical ionization (NH3‐CI) conditions using a mixture of perfluorinated alkanes (referred to commonly as perfluorokerosene or PFK) as the secondary mass reference even though these perfluorinated compounds do not form positive ions under NH3‐CI conditions. By creating a ‘composite’ spectrum of analyte under NH3‐CI conditions, and PFK under electron ionization (EI) conditions, while signal averaging in memory, mass measurement of the analyte peaks can be accomplished. Combined capillary gas chromatography/accurate mass measurements of components at sub‐part‐per‐million levels in environmental extracts are described as well as confirmation of novel eicosanoid structures.
A facile method for the localization of a double bond in aliphatic compounds
Authors: Schneider B. , Budzikiewicz H.
Published: May 2005

Olefinic aliphatic compounds can be transformed on a microscale into the corresponding epoxides by reaction with m‐chloroperbenzoic acid. The crude reaction mixture can be analysed without further work‐up, by gas chromatography followed by chemical ionization mass spectrometry or desorption chemical ionization mass spectrometry with nitric oxide as the chemical ionization gas.
Electron ionization mass spectrometry of synthetic C60
Authors: Luffer Debra R. , Schram Karl H.
Published: May 2005

Novel carbon clusters isolated in the solid phase have been characterized by electron ionization (EI) mass spectrometry. The crystalline material contains the C60 and C70 molecules in a ratio of 37:1. Both of these molecules form singly charged ions that appear at m/z 720 and 840, respectively, and doubly charged ions that appear at m/z 360 and 420, respectively. Only the C60 molecule produces the triply charged species, at m/z 240. C60 undergoes fragmentation by losing successive multiples of C2 through C16. The C70 molecule only loses the fragments C2 and C4. Collisionally activated decomposition of these molecules in the first field‐free region did not reveal any more extensive fragmentation than was observed under EI conditions.
Mass spectrometric investigation of 2‐aminopropiophenones and some of their metabolites
Authors: Pokrajac M. , Miljković B. , Bisailović B.
Published: May 2005

Complex metabolic mixtures of 2‐aminopropiophenones, obtained both after in vitro and human in vivo metabolism of these compounds, have been investigated using both mass spectrometry and gas chromatography/mass spectrometry. The mass spectrometric fragmentation schemes of the compounds have been proposed and verified. The schemes are based on the characteristic fragments obtained by alpha‐cleavage of these compounds using direct inlet mass spectrometry or gass chromatography/mass spectrometry. these findings were confirmed with chemical ionization mass spectrometry, when quasi‐molecular (MH+) ions were obtained as the highest relative abundane ions for all the compounds investigated, and were used in metabolic investigations of 2‐aminopropiophenones.
Matrix/sample interactions in ultraviolet laser‐desorption of proteins
Authors: Doktycz Stephen J. , Savickas Philip J. , Krueger Duane A.
Published: May 2005

Examination, by optical microscopy, of the matrix/analyte morphology of a sample propared from a droplet in matrix‐assisted UV laser‐desorption mass spectrometry (MUVLDMS) reveals that the matrix crystallizes to a large extent, thus altering the concentration of the material in regions on the surface from that of the bulk applied solution. Microscopy reveals that vanillic acid and to a lesser extent nicotinic acid matrices form prominent crystalline rings around the dried sample spot while sinapic acid forms a more uniform dispersion of the crystallized matrix. Insulin analyte investigated in this report tendss to form a thin isotropic phase in the center of the drops. The first reported use of a KrF excimer laser (249 nm) in MUVLDMS is also discussed.
Modification of a commercially available thermospray interface and its use for the analysis of sulfonated azo dyes by liquid chromatography/mass spectrometry
Authors: Groeppelin A. , Linder M. W. , Schellenberg K. , Moser H.
Published: May 2005

A standard commercial thermospray interface was modified by replacing the stainless‐steel capillary by another stainless‐steel capillary with a larger internal diameter. A fused‐silica capillary was then placed within the whole length of the stainless‐steel capillary and connected to the liquid chromatograph. A thermospray interface modified in this way exhibits a more inner surface, resulting in an increased sensitivity for analysing sulfonated azo dyes. Analysis of sub‐microgram quantities is possible only with the modified interface.
Molecular weight determination of a polyamidoamine Starburst polymer by electrospray ionization mass spectrometry
Authors: Kallos G. J. , Tomalia D. A. , Hedstrand D. M. , Lewis S. , Zhou J.
Published: May 2005

Electrospray ionization mass spectrometry has been demonstrated to be a useful technique for the molecular weight determination of a Starburst polymer. Mass spectra of multiply charged ions are deconvoluted to provide molecular weight information of many components in a non‐separated mixture. These data may also be used for determining a polydispersity value for this systhetic polymer system.
Suitability of fast‐ion bombardment mass spectrometry for the investigation of 1,4‐dihydropyridine derivatives
Authors: Hamdan M. , Scandola M. , Franchi D. , Tarzia G. , Gaviraghi G.
Published: May 2005

Positive/negative fast‐ion bombardment (FIB+/FIB−, negative‐ion chemical ionization (CI−) and positive‐ion electron ionization (EI+)mass spectrometry are used to investigate a number of 1,4‐dihydropyridine derivatives. The FIB+ mass spectra presented, acquired at fixed Cs+ ion‐gun voltage as well as at different voltages ranging from 1–16 kV, display a close resemblance to their EI+ mass spectral counterparts. Comparison of the FIB− data with data acquired in ammonia CI− demonstrates that for the type of compound investigated in this work, the latter ionization technique yields a superior molecular anion signal and negligible fragmentation. Some of the FIB+ mass spectra presented display a number of unmistakeable qualitative differences which are tentatively attributed to the isomeric stereo‐chemistry of the compounds investigated.
Cationization of destruxins (cyclodepsipeptides) under fast‐atom bombardment
Authors: Lange C. , Mulheim C. , Vey A. , Pais M.
Published: May 2005

Cationization ability is presented using fast‐atom bombardment mass spectrometry and fast‐atom bombardment tandem mass spectrometry. The sodium cation has the best potential for cationizing A‐ and E‐destruxins (cyclodepsipeptides), E‐destruxin having a greater ability to cationize with Na+ than A‐destruxin.
Formation and decay of doubly charged ions from polycyclic aromatic hydrocarbons and related compounds
Authors: Hagan D. A. , Eland J. H. D.
Published: May 2005

Coincidence techniques have been used to investigate double photoionization and subsequent decay of a series of polycyclic aromatic hydrocarbons (PAHs) from benzene to perylene. At fixed photon energy (40.8eV) the total yield of double ionization relative to single photoionization for both PAHs and for aliphatic compounds increases asthe same function of the excess energy above the double ionization energy. The ratio of double to single ionization for a given compound at different photon energies varies linearly with the excess energy. The fraction of dissociative double photoionization falls with increasing size in the PAH series; the ejection of characteristic neutral species (H˙, H2 and C2H2) is the main dissociation pathway in the larger PAHs while charge separation is important for smaller species. Partial hydrogenation or aliphatic substitution results in decreasing stability of the doubly charged ions and increasing dissociation.
Fast‐atom bombardment mass spectrometry of oligomeric dicyanobis(polypyridine) ruthenium (II) complexes
Authors: Bignozzi C. A. , Bortolini O. , Traldi P.
Published: May 2005

The positive‐ion fast‐atom bombardment (FAB) mass spectra of the biniclear [CNRu(L2)CNRu(L'2)CN]+ and trinuclear [CNRu(L2)CNRu(L2CNRu(L2)CN]2+ complexes (L=2,2′‐bipyridine; L' = 2,2′‐bipyridine or 1,10‐phenanthroline) have been investigated and compared with those of the mononuclear NCRu(L'2CN species. The FAB fragmentation patterns of the mononuclear species are interpreted by a combination of simple losses of neutral polypyridine ligands andHCN molecules and provide useful information for the understanding of the gas‐phase decomposition of the oligimeric species.
Measurement of gas‐phase binding energies of crown ethers with metal ions by Fourier‐transform ion cyclotron resonance mass spectrometry
Authors: Katritzky Alan R. , Malhotra N. , Ramanathan R. , Kemerait R. C. , Zimmerman Jaffrey A. , Eyler John R.
Published: May 2005

Complexes of the type [crown+M]+ were observed following laser desorption ionization of 18‐crown‐6 molecules ‘doped’ with K+, Cs+, and Ba+. Laser desorption ionization of 15‐crown‐5 and 12‐crown‐4 ‘doped’ with the same metals gave [(crown)]2+[M]+ type sandwich complexes. Binding energies of crown ethers with different metal ions in all such complexes have been estimated from appearance energies obtained in the collisionally‐activated dissociation of the corresponding laster desorbed complexes.
Dissociation of positively‐charged apliphatic epoxides. III. [C4H8O]+˙ eposides and α, β unsaturated ethers
Authors: Berruyer‐Penaud Florence , Bouchoux Guy , Tortajada Jeanine
Published: May 2005

Unimolecular dissociation of the molecular cations of 1,2‐expoxybutane (1), 1‐methoxypropene (2), 2,3‐epoxybutane (3), ethyl‐vinyl ether (4), 1,2‐epoxy‐2‐methylpropene (5), and 2‐methoxypropene (6)have been investigated. Different behaviour of pairs of [C4H8O]+˙ isomers (1+˙/2+˙), (3+˙/4+˙) and (5+˙/6+˙) have been demonstrated. Isomerization by epoxide ring opening and 1,4‐hydrogen migration is suggested to explain the similar unimolecular chemistry observed for the two partners of each pair of isomers.
Investigation of singly charged dihalomethanes by collision spectroscopy
Authors: Bortolini O. , Hamadan M. , Traldi P.
Published: May 2005

Translational energy spectrometry (TES) and collision‐induced dissociation (CID) experiments on the singly charged ions, CH2CI2+˙, CH2Br2+˙ and CH2I2+˙ have been performed on a double‐focusing mass spectrometer. No TES peaks could be seen from CH2CI2+˙ due to inadequate sensitivity. The measured energies of a number of non‐dissociative electronic states of the incident ions of CH2ID2+˙ and CH2Br2+˙ are in agreement with energies reported by photoelectron spectroscopy. The latter technique indicates the presence of a weak band in the photoelectron spectrum kof CH2Br2 lying 8.4–9.4eV above its ground state. This band is evident in the TES spectrum of CH2Br2+˙ incident ions. Other electronic ststes are also observed and tentatively assigned.
Are gas‐phase processes really responsible for the ionization of cyclic acetals by fast‐atom bombardment?
Authors: Paul Gary J. C. , Bourg Serge , Bertrand Michel J.
Published: May 2005

The mass spectral behavior of a series of substituted 2‐phenyl‐1,3‐dioxolanes has been studied by several ionization techniques in order to gain further insight into the basic ionization mechanisms occurring in the fast‐atom bombardment mass spectrometry. The results obtained show that in chemical ionization, ions of the type [M+H]+ are predominant while [MH]+ ions are observed as important species in electron ionization and fast‐atom bombardment. Comparison of the gas‐phase hydride‐ion affinities of thr chemical ionization reagent gases ammonia and isobutane with those of the loquid matrices glycerol and dithiothereitol/dithioerythritol indicates that the predomionant formation of the [MH]+ ion observed in fast‐atom bombardment by hydride abstraction in the gas phase is improbable. Furthermore, comparison of the electron ionization behavior of the cyclic acetals with that observed under fast‐atom bombardment suggests that the origin of [MH]+ in the latter is not related EI gas‐phase processes.
Analysis of saxitixin in urine by continuous‐flow fast‐atom bombardment mass spectromety
Authors: Mirocha Chester J. , Cheong Wonjo , Mirza Urooj , Kim Young Bae
Published: May 2005

An improved method of saxitoxin analysis in urine using continuous‐flow fast‐atom bombardment mass spectrometry was developed. Parameters studied were matrix composition, matrix flow, temperature of probe tip, probe‐tip design and sample extraxtion. Optimal detection was obtained using the following matrix composition: 5% glycerol, 0.5% acetic acid, 0.025% sodium dodecylsulfate, 0.1% polyethylene glycol (PEG) 400 and 0.5% PEG 300; probe‐tip temperature: (∼55°C); flow rate: 5 or 8μL per min.; probe tip: Olson‐Hogge design. The STX standard was detected at 200pg with signal‐to‐noise ratio of 11. The percent recovery of saxitoxin from human urine after clean‐up on a weak cation exchange column was 75%.
Characterization of [C6H7N]+˙ radical cations by tandem mass spectrometry
Authors: Flammang Robert , Thoelen Olivier , Quattrocchi Calogero , Bredas Jean‐Luc
Published: May 2005

Collisional Activation, charge‐stripping and neutralization/reionozation mass spectra allow the identification of six [C6H7N]+˙ isomers, namely the molecular ions of the three isomeric picolines, 1+˙–;3+˙, ionized 2‐ and 4‐methylene dihydropyridines, b—c, and ionized pyridinium methylide, a. The implication of the distonic forms a and b in some fragmentation reactions of funct of onalized (position 2) pyyridines is briefly discussed. Molecular orbital calculations indicate the b>a>1+˙ stability sequence.
Negative‐ion chemical ionization—collision‐induced dissociation study of unsubstituted cycloalkanols, alkanones and alkenones at low collisional energy
Authors: Decouzon M. , Géribaldi S.
Published: May 2005

The collision‐induced dissociation reactions of the [M1]− and [M3]− ions of cyclopentanol, cyclohexanol, cyclopentanone, cyclohexanone, cyclopent‐2‐en‐1‐one and cyclohex‐2‐en‐1‐one have been studied under lowenergy collisional activation using a Fourier‐transform ion cyclotron resonance mass spectrometer, and compared to literature data obtained at lhigh‐energy and under single‐collision conditions. Some significant differences appear in these data, which are discussed. Moreover, a general scheme of fragmentations appears between the alcohol, ketone and enone functions.
Dyanmic ion trapping for Fourier‐transform ion cyclotron resonance mass spectrometry: Simultaneous positive‐ and negative‐ion detection
Authors: Gorshkov Michael V. , Guan Shenbeng , Marshall Alan G.
Published: May 2005

The conventional static electric potential used to trap ions fro fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry has been replaced by a low‐amplitude [as low as Vac≈︁0.5 V for N] alternating (17.5kHz) electric field applied to the end caps of an ICR ion trap. Ionz‐motion is then governed by a Mathieu equation, whose solution leads to az‐stability diagram for which optimal results are obtained atz‐stability parameter, qz= 4qλVac/(mω2)≈︁0.5, in whichm/qis the ion mass‐to‐charge ratio, Ω is the RF frequency, and λ=2.7737/d2for a cubic trap of edge length, d. A triangular waveform appears to be more effective than sinusoidal modulation. We demonstrate experimentally three major additional advantages of RF trapping for FTICR mass spectrometry: (a) both positive and negative ions may be trapped and detected simultaneously; (b) Magnetron motion is eliminated, along with the electrostatic radial field‐induced ICR frequency shift and sidebands; and (c) mass calibration follows a simpler law (m=a/v, in whichais a constant andvis the measured ICR orbital frequency) than for electrostatic trapping (m=a/v+b/v2, in whichaandbare constants). All prior FTICR mass spectrometric capabilities are preserved, except that (as in an RF‐only quadrupole ion trap) optimal sensitivity is observed only for 0.4⩽qz⩽0.7, so that the mass‐to‐charge ratio range for a single FTICR mass spectrum is limited accordingly.
On‐line liquid chromatography/thermospray mass spectrometry in the analysis of oligosaccharides
Authors: Niessen W. M. A. , van der Hoeven R. A. M. , van der Greef J. , Schols H. A. , Voragen A. G. J.
Published: May 2005

The analysis of intact neutral oligosaccharides by on‐line liquid chromatography/thermospray mass spectrometry is described. Molecular‐weight information on oligomers up to a degree of polymerization of 10 is obtained using an aqueous mobile phase containing 10−4 mol/L sodium acetate, which was found to be compatible with thermospray interfacing and ionization. Ions due to sodiated and disodiated oligosaccharides are observed under these conditions without fragmentation. The aqueous 10−4 mol/L sodium acetate mobile phase is demonstated to be applicable in the separation of mixtures of oligosaccharides on a reversed‐phase octadecyl‐modified silica column.
Matrix‐assisted laser desorption mass spectrometry of oligodeoxythmidylic acids
Authors: Huth‐Fehre T. , Gosine J. N. , Wu K. J. , Becker C. H.
Published: May 2005

Ferulic acid, sinapinic acid and 2,5‐dihydroxybendoic acid (DHBA) have been tested as matrix materials for matrix‐asserted laser desorption of the pure oligonucleotide pd(T)12 and a mixture of oligonucleotides pd(T)12 through pd(T)18 using pulsed 337 nm radiation combined with reflecting time‐of‐flight mass spectrometry. The three matrix materials are compared with respect to obtainable mass resolution, degree of fragmentation, and adduct formation, as well as the highest mass resolution.
Observation of the fullerene anions C and C by electrospray ionization
Authors: Hiraoka Kenzo , Kudaka Ichiro , Fujimaki Susumu , Shinohara Hisanori
Published: May 2005

Mass spectsrometric investigation on the fullerence C60 and C70 was performed using electsdrospray ionization. C, C60O, C, and C70O ions were detected by reducing C60 and C70 using Nak amalgam in benzene + dimethoxyethane solvent. C was found to be much more reactive than C in solution.
Evidence for a lysine‐specific fragmentation in fast‐atom bombardment mass spectra of peptides
Authors: Ackermann Bradley L. , Barbuch Robert J. , Coutant John E. , Krstenansky John L. , Owen Thomas J.
Published: May 2005

A fragmentation proccess observed for peptides that contain lysine, or other amino acids which possess a free amino group on their sidechain, is reported. The ions generated by this process are found 16 Da below the acylium‐type B ions that result from fragmentation at the C‐terminal side of lysine or other amine‐containing residues in fast‐atom bombardment (FAB) mass spectra. These ions, which are referred to as (B—16) ions, permit differentiation between the isobaric amino acids lysine and glutamine in peptide mass spectra. High resolution measurements indicate that (B—16) ions differ in composition from the corresponding B ions by the removal of one oxygen atom. Formation is believed to occur through a cyclization process initiated by nucleophilic attack by the free amino group of the lysine sidechain at the carbon of the acylium ion (B ion). A similar process initiated derectly from the protonated peptide may also occur. Analogous cyclization processes are restricted for glutamine because this residue is comparatively less nucleophilic than lysine (i.e., amide vs amine). Although (B—16) ions have been detected under high energy collisionally induced dissociation, they are formed less readily than by FAB mass spectrometry. A mechanism consistent jwith this observation as well as other experimental evidence is presented to account for the formation of (B—16) ions.
Electrospray‐ionization mass spectrometry for the detection of discrete peptide/metal‐ion complexes involving multiple cysteine (sulfur) ligands
Authors: Allen Mark H. , Hutchens T. William
Published: May 2005

Conditions have been developed to characterize the reversible interaction of one or more Zn(II) ions with cysteine (sulfur) ligands on metal‐binding peptides by electrospray‐ionization (ES) mass sspectrometry. A 71‐residue peptide with two separate clusters of four cysteine residues was selected as a model to optimize both the solution and electrospray variables most likely to affect the detection of stable cysteine (sulfur) ligland/Zn interactions. By infljusing peptide in water alone, stable elelctrospray and ion signals were produced in both the absence and presence of up to 100 uM zinc sulfate. In the absence of Zn(II), the callculated mass of the fully reduced peptide (8248.5 Da) was observed (8248.4±0.4 Da). In the presence of Zn(II), peptides with zero, one and two bound Zn atoms were detected; all three species were prelsent in several different charge states. The overall charge envelope was typically unchanged in the presence of Zn; the chaarge‐state optimum (10+) observed for this peptide dwas apparently unaffected by the dpresence dsof bound Zn. The interaction of Zn(II) ions with sulfur lilgands in this peptide appeared to result in tetracoordinate covalent bonds. In summary, these data suggest that (i) stable electrospray signals can be generated form high conductivity aqueous solutions of meltal ions; (ii) peptides with sulfur ligand/Zn complexas are stable to the ES ionization prolcess; (iii) bound Zn is not the primary source of charge and does not alter the observed charge‐envelope optimum; (iv) the relative distribution of peptide without bound Zn, with one bound Zn, and with two bound Zn atoms can be fully resolved in each of several different charge sltates; and (v) various solution factors affecting peptide/metal‐ion interaction stoichiomeltry can be investiged by ES. In conclusion, we believe dthat ES mass spectrometry is a powerful new method of evaluating a wide variety of specific biomolecular polymer/metal‐ion interactions.
Usefulness of fast‐atom bombardment and collision‐activated dissociation linked scan (B/E) mass spectrometry for structural investigation of indole alkaloids
Authors: Laprévote Olivier , Girard Christian , Das Bhupesh C. , Mukherjee Rabindranath
Published: May 2005

Positive‐ion fast‐atom bombardment (FAM) mass sspectrometry was used to ionize two indole alkaloids, namely trinervine and its quaternary metho‐salt venecurine containing a hemiketal ring system. Analysis of collision‐activated dissociation spectra by the technique of linked scanning at consltant B/E gave sturcturally useful information. Addition of concentratedf acid to the glycerol matrix yielded glycoside‐type derivatives from both compounds. These studies Provide further examples of an ‘acid effect’ on the protonation site of polyfunlctional molecules along with the possibility of their undergoing chemical mokification in the FAB matrix.
A method for uniform optimization of quadrupole pre‐filters
Authors: Trajber Csaba , Simon Miklós , Bohátka Sándor
Published: May 2005

Novel aspects of utilizing RF‐only pre‐filters in a quadrupole mass spectrometer are presented. Theoretical considerations converning the optimization of the spectrometer by means of the pre‐filter length and the ion entrance velocity are given and are given and are compared with the results of model calculations. Experimental results are shown to illustrate the advantages of the setup constructed according to the proposed optimization method over both the single mass filter and one with a pre‐filter of conventional length range. The most effectively focusing pre‐filters are shown to have integer multiples of an elementary length. The predictions have only been verified experimentally for helium. Apoproximeately 150% improvement was measured for helium transmission with respect to the single analyser with the suggestede parameters. Since the resolution always inporoves with length at a certain ion velocity, it is preferable to make use of some of the higher local minima of the suggestede optimizing function.
The components of the venom of a spider Scodra griseipes. 2. Structural information on biogenic amines using tandem mass spectrometry
Authors: Lange C. , Paris C. , Celerier M.‐L.
Published: May 2005

Biogenic amines, which are components of tarantula Scodra griseipes venom, are studied using tandem mass spectrometry. Their heptafluoropropionic (PFP) derivatives are ionized under electron impact and isobutane‐chemical ionization. Daughter‐and parent‐ion mass spectra under collisionally activated dissociation conditions provide a more detailed study of such derivatives. Discrimination of di(PFP)amines and tri and tetra(PFP)amines is possible because of the presence of diagnosis ions induced by collision.
Sequential product‐ion spectra (MS3 and MS4) with array detection and reaction‐intermediate scanning on a four‐sector mass spectrometer
Authors: Ballard Kevin D. , Gaskell Simon J. , Jennings Richard K. C. , Scrivens Jim H. , Vickers Richard G. , Boyd R. K.
Published: May 2005

Frangmentation yields during high‐energy collisionally activated decomposition (CAD) tandem mass spectrometie experiments are often low, due in part to the short time‐period available for the fragmentations. Consequently, attempts at multi‐stage mass spectrometry undeer high‐energy CAD conditions can give unsatisfactory result when a conventional point detector is used. Arry detection dramatically improves the detection of ion currents of low abundance; we therefore incorporated arry detection in a variety of sequential product‐ion ‘scanning’ experiments, including MS3 and MS4, using a BEBE instrument. The corresponding experiments were previously established on a BEqQ hybrid instrument. where the final stage of decomposition occurred under low‐energy CAD conditions. The results from the hybrid were used as a basis of comparison for the results under high‐energy CAD with array detection. On the BEBE instrument, the use of the array greatly enhanced the signal‐to background ratio for second‐and third‐generation product‐ion spectra, as compared to the use of the point detector on the instrument in several instances, the use of the array was criticaL to the success of the experiment on the four‐sector instrument. For the peptides analyzed, the fragmentation patterns observed in the sequential product spectra were similar on the four‐sector instrument and on the hybrid instrument, although the relative abundances differed between the high‐and low energy CAD regimes. Reaction‐intermediate scanning, involving two sequential decomposition step occurring on the microsecond high energy time scale, has also been implemented on the BEBE instrument. A New mode of reaction‐intermediate scanning has also been implemented on the BEqQ hybrid instrument, permitting it to access sequential fragmentation when both occur under high‐energy CAD conditions.
Differentiation between isomeric methylated purine derivatives by means of chemical ionization and collision‐induced dissociation
Authors: Curcuruto O. , Tarzia G. , Hamdan M.
Published: May 2005

A number of commercially available purine derivatives were investigated by means of chemical ionization in ammonia and methane reagent gases. The protonated molecules of the compounds investigated were mass selected and their collision‐induced dissociated (CID) spectra monitored using 100 eV collision energy. Competition between the protonation and addition reaction channels which yield MH+ and [M + NH4]+ ions and the major fragment ions observed in the CID spectra reflect certain stereochemical differences between the isomeric precusors investigated. The present work is an attempt to contribute to the continuous search for first and effective means of distinguishing between the various isomers of biomedically important classes of compounds.
Thin layer chromatography/mass spectrometry: The advantages of tandem mass spectrometry
Authors: Monaghan J. J. , Morden W. E. , Johnson T. , Wilson I. D. , Martin P.
Published: May 2005

The results of thin layer chromatography/mass spectrometry (TLC/MS) and thin layer chromatography/tandem mass spectrometry (TLC/MS/MS) experiments are described. Spectra from the analytes were obtained directly from the absorbent without the need for extraction prior to analysis by mass spectrometry. These results illustrate the added specificity that the tandem mass spectrometer can afford in the detection and characterization of a range of compounds separated by TLC.
Association of the acylium ion of acids with alcohols as an esterification mechanism in chemical ionization
Authors: Tu Ya‐Ping , Chen Yao‐Zu
Published: May 2005

The reactions between aliphatic acids and alcohols in the gas phase were investigated by chemical ionization (CL) mass spectrometry. The association of the acylium ion of acids with alcohols is suggested as an esterificaion mechanism under CI conditions in addition to the classical nucleophilic addition—elimination pathway.
Charge promotion of low‐energy fragmentations of peptide ions
Authors: Burlet Odile , Orkiszewski Ralph S. , Ballard Kevin D. , Gaskell Simon J. , Bertrand M. J.
Published: May 2005

We have examined the hypothesis that structural features which predispose to localization of charge at a strongly favored site are not conducive to the low‐energy fragmentation of peptide ions via a multiplicity of pathways. Consistent with this proposal, it is demonstrated that the formation of N‐ or C‐terminal pre‐charged derivatives is detrimenal to the formation of sequence‐specific product ions following low‐energy collisional activation. Protonation of pre‐charged derivatives (yielding doubly charged ions) restores favorable fragmentation properties; the effect is attributed to the fragmentation‐directing properties of the proton whih may occupy one of several sites. Similarly, a doubly protonated peptide which incorporates a C‐terminal arginine residue as a single strongly favored site of protonation exhibits favored low‐energy fragmentations attributable to locaton of he second proton at one of several sites remote from the C‐terminus.
Determination of active hydrogen in organic compounds by electron‐impact mass spectrometry
Authors: Dinya Zoltán , Lipták Miklós , Szabó Pál , Sztaricskai Ferenc , Vékey Karoly
Published: May 2005

We report here detailed studies of Bose et al.'s (J. Org. Chem. 47, 4008 (1982)) simple method for obtaining electron‐impact (EI) mass spectra from non‐volatile and/or thermolabile organic compounds by using ammonium salts. Good quality mass spectra can be obtained by mixing the analyte with different ammonium salts (mainly with NH4Cl) in a given ratio, the mixture being introduced through a conventonal direct probe. A wide variety of ammonium salts has been used to study the effect of the anion and to determine the optimum analyte:NH4X ratio and the other experimental parameters (i.e., electron energy, source temperature etc). A very simple and cheap means of determination of active hydrogen in hydroxyl, carboxyl, sulfhydryl, amino and amido etc groups by EI mass spectrometry using deuterated ammonium chloride (ND4CI) is described. The method is based on exchange of active hydrogen for deuterium occurring in situ in the ion source. This technique allows drect comparison of spectra before and after deuteration and the number of active hydrogens can be identified in most cases. The applicability of this method is demonstrated on different model compounds.
Relative affinities of alkylnitriles for the CoCl+ ion in the gas‐phase
Authors: Chen Lin‐Zhi , Miller Jack M. , Murthy Vemisetty S.
Published: May 2005

The relative CoCI+ ion affinities of six alkylnitriles have been estimated using Cooks' kinetic method in mass spectrometer using fast‐atom bombardm ent ionization. An approximate ordering for the relative affinities is given and discussed.