bluuebunny/crossref_metadata_2025_split huggingface dataset:
Detection of nitrotoluene isomers by ion cyclotron resonance mass spectrometry using ion/molecule reactions with NO+ as reagent
Authors: Xu Guoying , Herman Jan A. , Harrison A. G. 
Published: May 2005

AbstractIon/molecule reactions in nitrotoluene/NO and nitroluene/OCS systems were studied in an ion cyclotron resonance mass spectrometer. The formation of an adduct ion between m‐nitrotoluene and NO (or OCS to a lesser extent) differentiates it from the o‐ and p‐nitrotoluene isomers can be distinguished by their different decomposition rates into C7H6NO+ and C7H6NO+ fragment ions.
Doubly ionized states of CH4 studied by double‐charge‐transfer and auger‐electron spectroscopies
Authors: Griffiths W. J. , Svensson S. , Naves de Brito A. , Correia N. , Langford M. L. , Harris F. M. 
Published: May 2005

AbstractHigh‐resolution double‐charge‐transfer spectroscopy has been used to measure the double‐electron‐capture reactions with CH4. Using kilo electron volt OH+, CI+ and F+ projectile ions it is possible in double‐electron‐capture reactions with CH4 molecules to populate the ground triplet state of CH. The energy of this state relative to the gound state of CH4 is found to be 38.2±0.4 eV, while the fiest excited triplet state is found at a double‐ionization energy of 46.7±0.8 eV. In double‐electron‐capture reactions involving H+ projectile ions and CK4 molecules, low‐lying singlet states of CH are populated. The energies of the four lowest singlet states in CH were measured to be 39.2±0.4, 40.5±0.4, 42.1±1 and 51.0±1 eV. High‐resolution photon‐induced Auger‐electron spectra of the CH4 molecule have been recorded. The KLL Auger Spectrum shows four distinct structures in the 30–70 eV double‐ionization evergy range centred at 40.3±0.1, 47.03, 53.2±0.3 and 6.9±0.3 eV. The previously published data on CH have been reviewed.
How are ions formed from electrosprayed charged liquid droplets?
Authors: Hiraoka Kenzo 
Published: May 2005

AbstractThe dependence of ion intensities on capillary position has been investigated for electrosprayed solutions of 5 × 10−6M (CH3)4 NBr and 10−3M CH3COOH in CH3OH+H2O+CCI4. It was found that the efficiencies for desorption from the charged liquid droplets into the gas phase are in thE order (CH3)>NH>CH3OH. The intensities of ions with higher desorption efficiencies become strong near the periphery of the spray cone, whereas those with lower desorption efficiencies have maxima in the central region of the spray cone. With increase of the vertical distance between the capillary tip and the sampling orifice, the distribution of the space‐charge density becomes nearly uniform in the spray cone due to the space‐charge field.
Probing vibrational modes in a neutral triatomic molecule by high‐resolution translational‐energy spectrometry
Authors: Mathur D. , Wilkins A. C. R. , Brenton A. G. 
Published: May 2005

AbstractHigh‐resolution translational‐energy spectrometry has been applied to study vibrational excitation in neutral CO2 in its ground electronic state by 3 ke V impact by O+, N+, Ne+, Ar+ and Xe+ projectile ions. Three quanta of asymmetric stretch mode are excited. Bending mode vibrational excitation also manifests itself in translational‐energy spectra obtained with the heavier projectile ions (Ne+, Ar+ and Xe+). In the case of the O+ projectiles, simultaneous electronic (O+,2D⇔︁2P) and vibrational (CO2, ν3=0→1) excitation is also observed.
Improved accuracy of mass measurement with a quadrupole ion‐trap mass spectrometer
Authors: Williams Jon D. , Cooks R. Graham 
Published: May 2005

AbstractMass Measurement accuracy of better than 0.015% on protonated gramicidin S (nominal chemical average molecular weight 1141.5 Da) and its first three isotopes has been achieved using reasonant ion ejection in the quadrupole ion‐trap mass spectrometer operated at unit resolution. Analyte and Calibrant ions are subjected to identical injection and trapping conditions when desorbed by Cs+ ions from a split prone‐tip and co‐injected into the trap. When the mass analysis scan rate is slowed, enhanced resolution is achieved for all ions but the mass range accessed in a single scan of the digital‐to‐analog converter, which controls the mass analysis scan, is limited making calibration difficult. A peak‐matching procedure is described for use at these higher resolution conditions in which the offset voltage which determines the origin of the RF amplitude ramp is adjusted in such a fashion that the analyte and calibrant ions occur at the same point in the mass analysis scan. This procedure gave an improved mass measurement accuracy of better than 0.007% for the protonated gramicidin S. ions.
On‐line isotachophoretic analyte focusing for improvement of detection limits in capillary electrophoresis/electrospray mass spectrometry
Authors: Tinke A. P. , Reinhoud N. J. , Niessen W. M. A. , Tjaden U. R. , van der Greef J. 
Published: May 2005

AbstractDetectability enhancement in capillary electrophoresis/mass spectrometry (CE/MS) has been realized using on‐line isotachophoretic (ITP) analyte focusing. This is demonstrated for the analysis of a mixture of anthracyclines, showing on at least 200‐fold improvement detectable concentration for ITP/CE/MS compared to CE/MS using an electrospray (ESP) interface.
Unequivocal discrimination between consecutive and competing collisionally induced decompositions in an ion trap
Authors: Paradisi Cristina , Todd John F. J. , Traldi Pietro , Vettori Umberto 
Published: May 2005

AbstractDiscrimination between consecutive and competing collisionally induced decomposition (CID) reactions can easily be obtained by a new pocedure consisting of the collisional activation of a parent ion and the simultaneous ejection of one of its daughter ions in an ion trap. This is done by applying, during a single storage phase, a DC voltage appropriate to induce fragmentation (‘boundary’ activation) of the parent and, at the same time, a ‘tickling’ RF potential, sufficient to eject a selected daughter ion rapidly from the trap. Several examples are reported which illustrate the capabilities of the procedure in establishing fragmentation pathways e.g., to determine whether a daughter ion is formed in a stepwise process involving an intermediate primary fragment rather than from the direct fragmentation of the parent ion. Salient features of this technique are discussed.
Analysis of pesticides using liquid chromatography/atmospheric‐pressure chemical ionization mass spectrometry
Authors: Doerge Daniel R. , Bajic Steve , Millington D. S. 
Published: May 2005

AbstractSeventeen pesticides in five chemical classes (triazines, phenylureas, carbamates, organophosphates, miscellaneous) from the US Environmental Protection Agency's National Pesticide Survey of groundwater contaminants were selected for analysis by atmospheric pressure chemical ionization (APCI‐MS). The spectra obtained from most compounds consisted solely of [M + H]+ in positive‐ion mode. One example, p‐nitrophenol produced only the [M − H]− ion in negative‐ion mode. Increasing the potential on the sampling cone effected voltage‐dependent fragmentation of all carbamates ad alachlor to form diagnostic daughter ions. Detection limits (Limit of detection (LOD), signal‐o‐noise ratio=3) in full‐scan or selected‐ion monitoring mode varied from 0.8–10 ng of 0.01‐1 ng, respectively, and calibration curves were highly linear from the LOD to 100 ng. Mobile phase composition (50–100% acetonitrile in water) and flow rate (0.24 and 1.25 mL/min) had small effects on sensitivity of response. These reslts suggest that the sensitivity of APCI‐MS is affected less than that for thermospray and particle beam LC/MS by chemical differences in analyte structure for the pesticide classes tested. The low detection limits, high degree of linearity, the ability t produce diagnostic fragment ions using cone voltage fragmentation and the inter‐class versatlity suggest that APCI is a valuable technique for multiresidue confrmations of pesticides in groundwater.
Ion detection limitations to mass resolution in matrix‐assisted laser desorption time‐of‐flight mass spectrometry
Authors: Brown R. S. , Gilfrich N. L. 
Published: May 2005

AbstractThe ion detection process in a discrete‐dynode electron multiplier can result in significant mass resolution losses in time‐of‐flight mass spectrometry (TOF‐MS) for higher mass‐to‐charge (m/z) ion species. This resolution loss is attributed to propagation time delays and signal broadening in the ion detector. This is presumed tobe due to the generation o a distribution of secondary ion species produced initially upon impact of a primary ion with the first ynoe surface of the ion detector. Comparisons are made between the signals produced by a standard discrete dynode ion detector (which amplified the negatively chqrged species produced by impact of a primry ion) and a detector modified to respond to only the positively charged secondary ion species produced by a primary ion impact. Ion signals for higher m/z ions with the standard detector geometry are see to be due to a narrow signal component, most likely due to the generation o secondary electrons and/or very low mass secondary ions (H−), and a broad signal component, apparently due to secondary ions which take signifiant amounts of time to traverse the low potential fields between the first and second detector dynode. This results in ion signal tailing for higher m/z ion species. Numerical subtraction of the ion signal obtained with the standard and modified detector geometries (singly protonated molecular ion species of equine myoglobin) results in an improvement in mass resolution, such that a new adduct ion species (from trifluoroacetic acid) can be resolved.
Thermally assisted electrospray interface for liquid chromatography/mass spectrometry
Authors: Lee Edgar D. , Henion Jack D. 
Published: May 2005

AbstractAn electrospray interface for liquid chromatography/mass spectrometry (LC/MS) is described that combines the direct heating of High‐performance liquid chromatography (HPLC) effluent that is characteristic of thermoooospray‐type interfaces. This interface is called the thermally assisted electrospray interface for LC/MS. The device can accept the total effluent from a liquid chromatograph at flow rates ranging up to 500 μL/min. The HPLC effluent is nebulized into charged droplets by a combination of heat and an applied electric field. Ions emitted from charged droplets are mass‐analyzed by a triple quadraupole mass spectrometer equipped with an atmospheric pressure ion sampling orifice. Singly or multiply charged ions, indicating the molecular weight of a sample, are observed with minimal fragmentation. The extent of multiple charging observed in electrospray and ion spray mass spectrometry is decreased somewhat in thermally assisted electrospray. Labile compounds which undergo thermal decomposition by conventional thermospray show no decomposition with thermally assisted electrospray.
A novel derivatization method for peptides to increase sensitivity and backbone fragmentation in liquid secondary‐ion mass spectra
Authors: Kiplinger Jeffrey P. , Contillo Leonard , Hendrick W. Lee , Grodski Alex 
Published: May 2005

AbstractDerivatization is used to increase both negative‐ion sensitivity and positive‐ion sequence information in the liquid secondary‐ion mass spectra (LSIMS) of a series of peptides. The derivatization method involves acylation with pentafluorobenzyl fluoride in a single‐step reaction, and the reaction mixture is applied directly to the probe tip for analysis. Acylation takes place at the unprotexted N‐terminus, tyrosine, and lysine. The derivatives exhibit increased signal‐to‐noise ration for [MH]− ions, especially where there is not already an acidic amino acid residue in the peptide. In positive‐ion LSIMS, the N‐terminal group acts to retain the charge at the N‐terminus, simplifying the fragmentation by producing N‐terminal fragment ions. It also increases positive‐ion fragmentation, sometimes very dramatically, making sequence determination more straightforward. The simplicity of the process, together with the enhancements it provides, make3 this a generally useful method for obtaining peptide structural information.
An investigation into the electron‐ionization‐induced mass spectrometric behaviour of some trans‐ and cis‐substituted cycloalkylamines of pharmaceutical interest
Authors: Anchisi Carlo , Fadda Anna Maria , Maccioni Anna Maria , Maccioni Elias , Favretto Donata , Traldi Pietro 
Published: May 2005

AbstractThe electron‐ionization‐induced mass spectrometric behaviour of eight cyclopentylamine and cyclohexylamine derivatives, recently synthesized, has been investigated by means of accurate mass measurements and metastable ion studies. These approaches allowed an easy structural characterization of the title compounds. In particular, mass‐analyzed ion kinetic energy spectroscopy proved effective for the differentiation of cis‐ vs trans‐isomers.
Improved methodology for liquid chromatography/continuous flow secondary‐ion mass spectrometry: Quantitation of abscisic acid glucose ester using reaction monitoring
Authors: Hogge Lawrence R. , Balsevich John J. , Olson Douglas J. H. , Abrams Garth D. , Jacques Suzanne L. 
Published: May 2005

AbstractImprovements in methodology for liquid chromatography/continuous flow secondary‐ion mass spectrometry (LC/CFSIMS) are described. Practical procedures have been developed for the preperation of packed fusedsilica capillary liquid chromatography columns and the coupling of these columns to the CFSIMS probe. A modified probe tip is described that significantly reduced ion beam instability arising from acceleration voltage discharge, changes in mobile phase composition during gradient elution, and uneven tip wettability. Interfering matrix background ions in LC/CFSIMS experiments are eliminated by reaction monitoring: the detection limit of the plant hormone metabolite, abscisic acid glucose ester, ABAGE is below 100 pg (235 fmol) with this technique. Reproducibility for quantitation is achieved by parallel reaction monitoring of the analyte and an added internal standard, ABAGE‐d6. The d6/d0 ABAGE response ratio for the monitored transitions is linear over the range 100 pg to 10 ng of injected ABAGE.
Matrix‐assisted laser desorption mass spectrometry of cytochromes P450
Authors: Lewis Sydell , Korsmeyer Katy Kuo , Correia Maria Almira 
Published: May 2005

AbstractMatrix‐assisted laser desorption ionization on a time‐of‐flight (MALDI/TOF) mass spectrometer provides a rapid and accurate method for molecular weight determination of hydrophobic cytochrome P450 proteins (P450s). A mass accuracy of 0.075% was achieved by analysis of dialyzed P450 2B1 using bovine serum albumin (BSA) as an internal standard. The measured mass of cytochorme P450 2B2 with MALDI/TOF resulted in an average molecular weight which was higher than reported values. Immobilization procedures proved extremely effective on samples containing high concentrations of phosphate buffers.
The use of hydrogen‐deuterium exchange to facilitate peptide sequencing by electrospray tandem mass spectrometry
Authors: Sepetov Nikolai F. , Issakova Olga L. , Lebl Michal , Swiderek Kristine , Stahl Doughas C. , Lee Terry D. 
Published: May 2005

AbstractThe utility of hydrogen‐deuterium exchange for sequencing peptides by mass spectrometry is demonstrated. The number of exchangeable hydrogens in a peptide is readily obtained by electrospray analysis of the peptide dissolved in deuterated solvents. This information can be used, in conjunction with published computer algorithms for interpreting peptide mass spectra, to reduce significantly the number of candidate sequences that fit the experimentsl data. This information, when combined with fragment‐ion information in the mass spectrum, greatly increases the reliability of sequence determination.
Stereospecific Retro‐Diels‐Alder reactions in the negative‐ion mass spectra of Diels‐Alder adducts of substituted p‐benzoquinones and glucofuranodienes
Authors: Madhusudanan K. P. , Dhami T. S. , Rani A. , Suryawanshi S. N. 
Published: May 2005

AbstractThe negative ions of cis‐ and trans‐Diels‐Alder adducts of p‐benzoquinones and glucofuranodienes enable these stereoisomers to be differentiated because the cis‐ isomers undergo a highly‐favoured retro‐Diels‐Alder reaction.
Vaporization processes of borosilicate coatings studied by high temperature mass spectrometry and using an induction plasma generator
Authors: Stolyarova V. L. , Archakov I. Yu. , Gordeev A. N. , Yakushin M. I. , Shultz M. M. 
Published: May 2005

AbstractA new approach has been applied to study processes which take place during the thermochemical action of air (or other) plasma on heat protection materials. Vaporization processes of the borosilicate coating of ‘Buran's’ heatprotective tiles, both the initial state and after rf‐entry simulation testing (up to 100 landings), were investigated by the Knudsen mass spectrometric effusion method. Modelling of the thermochemical action of the shock‐layer plasma onto the front surfaces of real‐scale tiles was carried out by using an induction plasma genetor of 500kW power. It was established that the thermochemical action of the plasma causes, essentially, a decrease of vapour pressure over the coating. However, despite this decrease, the pressures observed are significantly higher than those over the SiO2–B2O3 system at the same temperature, due to gas‐phase SiO production by reaction between boron and silicon oxides and SiB4, which are contanied in the coating. The data available aiiow one to postulate the presence of the SiBO molecule in the gas phase. Data on mass‐loss rates obtained by direct measurments after re‐entry simulation compared nwell with the values calcuted from mass spectrometric data. It is suggested that the difference observed is caused by thermochemical action of atomic oxygen on the coating.
Structural investigation of the hydroxy‐propynal molecular ion
Authors: Pandolfo L. , Paiaro G. , Somogyi Á. , Catinella S. , Traldi P. 
Published: May 2005

AbstractA formyl ketenyl platinum derivative, trans‐μ1‐(PCy3)2(H)Pt[C(CHO)CO] (where Cy represents a cyclohexyl group), when reacted with HCl, gives a C3H2O2 species among the reaction products. The structure was investigated mass spectrometrically by study of the reactions of metastable ions, and the information gained was combined with data from theoretical calculations to rationalize the structure of the C3H2O2 molecule.
An ion‐trap mass spectrometric study on electron impact and collisionally induced decomposition pathways of some phenothiazine S‐oxides
Authors: Guidugli F. , Curcuruto O. , Traldi P. , Hegedus‐Vajda J. , Tamas J. , Taulov I. G. 
Published: May 2005

AbstractThe electron ionization (EI) mass spectra and the daughter‐ion spectra of the EI‐generated main fragments of phenothiazine S‐oxides and its two N‐substituted derivatives have been studied by means of ion‐trap mass spectrometry (ITMS). Interesting differences with the data already published on the same molecules as obtained by a magnetic sector instrument have been rationalized by considering how, under ITMS conditions, charge exchange or self‐chemical‐ionization phenomena can take place, leading to molecular species with low energy content.
Mass spectrometric studies of some new hafnocene dialcoholates
Authors: Grafov Andrèi V. , Favretto Donata , Traldi Pietro , Battiston Giovanni A. , Porchia Marina , Rossetto Gilberto , Zanella Pierino 
Published: May 2005

AbstractThe electron ionization mass spectrometric behaviour of a new class of hafnocene dialcoholates, and, for comparison, of hafnocene dichloride, is discussed. They are also compared on the basis of mass‐analysed ion kinetic energy spectrometry. Fragmentation patterns of oxygen‐containing species give relevant information on their potential as precursors for the deposition of HfO2 thin films via metal‐organic chemical vapour deposition.
Randomization in the fragmentation of benzophenone
Authors: Srzić Dunja , Martinović Suzana , Vujanić Predrag , Meić Zlatko 
Published: May 2005

AbstractThe hydrogen and carbon randomization in the mass spectrometric behaviour of benzophenone has been studied by deuterium and 13C‐labelling. Hydrogen scrambling is involved only in the reactions of primary loss of hydrogen from molecular ions, as well as in secondary elimination of two hydrogen atoms from [MCO]+· ions. The carbon randomization does not feature in benzophenone upon electron impact.
Antisense DNA oligonucleotides I: The use of ionspray tandem mass spectrometry for the sequence verification of methylphosphonate oligodeoxyribonucleotides
Authors: Baker Timothy R. , Keough Thomas , Dobson Roy L. M. , Riley Timothy A. , Hasselfield Jody A. , Hesselberth P. Eric 
Published: May 2005

AbstractThe sequences of synthetically prepared methylphosphonate oligodeoxyribonucleotides have been verified using ionspray tandem mass spectrometry with sample introduction via flow injection. The technique involves the use of product‐ion scans from multiply protonated (4+ and 5+) precursors. Among the ions detected are several series of fragments of different charge states that indicate the base sequence of the intact molecule. Oligomers as large as 18 bases have been successfully characterized.
Antisense DNA oligonucleotides II: The use of matrix‐assisted laser desorption/ionization mass spectrometry for the sequence verification of methylphosphonate oligodeoxyribonucleotides
Authors: Keough Thomas , Baker Timothy R. , Dobson Roy L. M. , Llacey Martin P. , Riley Timothy A. , Hasselfield Jody A. , Hesselberth P. Eric 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization (MALDI) mass spectrometry has been used to measure accurately the molecular masses of synthetic methylphosphonate oligodeoxyribonucleotides, up to 18 nucleotides in length. A simple method has been developed for the complete sequence verification of these compounds, which are intractable by classical means. Sequencing from the 5′ end of the molecule is possible because of inefficiencies in the synthetic procedure. Complementary information from the 3′ end can be obtained by partial hydrolysis of the methylphosphonate backbone.
Determination of sulfated peptides via prompt fragmentation by UV matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Talbo Gert , Roepstorff Peter 
Published: May 2005

AbstractDetermination of sulfation on peptides is difficult by biochemical methods if only a few picomoles of sample are available. By varying the laser irradiance, matrix‐assisted laser desorpiion/ionization mass spectra were obtained containing fragment ions diagnostic of sulfation.
A novel differentially pumped design for atmospheric pressure ionization‐ion trap mass spectrometry
Authors: Mordehai Alex V. , Henion Jack D. 
Published: May 2005

AbstractA novel differentially pumped design for atmospheric pressure ionization (API)‐ion trap mass spectrometry is described. The vacuum system consists of three stages of pumping: API interface stage (1060 L/min), ion trap vacuum region (520 L/s) and electron multiplier region (60 L/s). The ion trap vacuum chamber has been specially designed to implement differential pumping of the ion trap and electron multiplier regions thus allowing ion trap operation with unit mass resolution at pressures up to 6 × 10−3 Torr of helium while maintaining high vacuum in the electron‐multiplier detector region. Trapping efficiency for accumulating externally produced ions was studied at unusually high pressures of the damping gas (helium) up to a pressure of 7 × 10−3 Torr (medium vacuum region). The trapping efficiency for externally produced ions and hence the overall mass spectrometric sensitivity is significantly improved by the introduction of helium damping gas into the ion trap region up to 6 × 10−3 Torr.