bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resolution enhancement and parameter estimation in fourier analysis
Authors: Balcou Y. 
Published: May 2005

AbstractResolution in Fourier spectra can be significantly enhanced by displaying magnitudes of the complex peak derivatives with respect to frequency. These derivatives are computed by the judicious application of a new kind of windows, which reduce peak widths. When thus sharpened peaks are purely Lorentzian, then simple linear or parabolic regressions allow one to compute their parameters. A Fourier‐transform ion cyclotron resonance mass spectrometric example of such an improvement is presented.
Screening and characterization of atrazine metabolites by liquid chromatography/tandem mass spectrometry
Authors: Nélieu Sylvie , Stobiecki Maciej , Kerhoas Lucien , Einhorn Jacques 
Published: May 2005

AbstractThe ability of liquid chromatography combined with positive‐ion low‐collision‐energy tandem mass spectrometry for screening and characterization of atrazine metabolites in aqueous solutions is examined. The strategy used was defined after investigations on the structure and origin of the main daughter ions through experiments done by desorption chemical ionization with NH3 or ND3 as reagent gas. Following this, a three‐step procedure was proposed which included parent‐ion spectra based on [XCNC(NH)NH2]+ (with X  Cl or OH) ions apparently formed via ion‐dipole complexes and found to be highly diagnostic for chlorotriazines and hydroxytriazines respectively.
Isotope ratio mass spectrometry: Analysis of wines from different european countries
Authors: Bréas Olivier , Reniero Fabiano , Serrini Giorgio , Martin G. J. , Rossmann A. 
Published: May 2005

AbstractNatural stable isotope ratios for carbon, hydrogen and oxygen depend on the origin of the studied chemical compound. Such a precept is the basis of the control of the authenticity of food and especially alcoholic beverages. 13C/12C analysis of ethanol as well as 18O/16O determination of water contained in wines from different European countries underline the importance of the photosynthetic pathway as well as of the environmental and climatological conditions of the vine. Interesting results in agreement with isotopic fractionation rules for the geographical origin of the samples were obtained. That encouraged us to propose the establishment of a database for isotopic parameters in wines.
Effect of resolution on the shape of mass spectra of proteins: Some theoretical considerations
Authors: Werlen Raymond C. 
Published: May 2005

AbstractA small computer program has been written to investigate the effect of increasing the mass resolution to very high values (106) on the shape of mass spectral peaks of small to medium‐sized proteins. Previous work in this area has generally limited discussion to mass resolutions of a few thousand. Now that mass spectra of proteins are obtainable with a mass resolution exceeding one million, it is important to be able to conveniently generate theoretical spectra at the same resolution.
Mass spectrometric investigations of fullerenes. I. Vapour pressure over the C60/C70 binary system
Authors: Popović Arkadij , Dražič Goran , Marsel Jože 
Published: May 2005

AbstractThe absolute vapour pressures over pure C60, C70, fullerite and over the binary C60/C70 system are calculated from ion intensities vs. temperature up to 800 K using the Knudsen effusion mass spectrometric method. The vapour pressures (Pa) of C60 and C70 are given as a function of temperature (K) by the equations:

Corresponding Second Law enthalpy and entropy changes for sublimation are:

Results are discussed in terms of sample purity and pretreatment and correlated with data obtained by other authors. Fullerenes containing residual organic solvents (fullerite) partly decompose upon thermal treatment to amorphous carbon.
Control of internal proton transfers on ion‐dipole complexes from [MH]− ions of diphenol esters
Authors: Fournier F. , Perlat M.‐C. , Tabet J.‐C. 
Published: May 2005

AbstractThe behaviour of 3′,4′‐dihydroxybenzyl fatty acid ester towards the NH3/NH system has been investigated under negative‐ion chemical ionization (NICI) conditions. Under NICI, proton abstraction takes place regioselectively at one phenol site rather than from the enolizable position. Analysis of specific fragmentations of the isotopically labelled phenoxide species prepared in the gas phase by ND3 indicates that isomerization into an ion‐dipole intermediate (via charge‐promoted cleavage) takes place prior to fragmentation. Its dissociation provides fatty acid carboxylate ions (the charge is stabilized by coiling of the side chain). The acidity of the phenol group must be enhanced by the presence of a second group at the position ortho to the first. This explains why the previous ion‐dipole complex isomerizes by proton transfer into a second isomeric form which decomposes yielding the phenoxide species, as shown by labelling experiments. Stabilization of the negative charge by hydrogen bonding (ArO−…︁H+…︁O−Ar) from the phenoxide form is possible. A similar situation characterizes 3′,4′‐dihydroxybenzyl phenyl ethyl ester and 3′,4′‐dihydroxybenzyl benzyl ester. Their behaviour was also studied to find the influence of the side chain structure on the pathway of ion‐dipole dissociation under low‐energy collision conditions.
Utility of organic bases for improved electrospray mass spectrometry of oligonucleotides
Authors: Greig Michael , Griffey Richard H. 
Published: May 2005

AbstractThe sensitivity and accuracy of the mass spectrometric analysis of oligonucleotides using electrospray ionization can be compromized when the oligomer is adducted in the gas phase to cations such as sodium or potassium. We have evaluated the addition of mM concentrations of a series of organic bases with solution pKb values ranging from 11.5 to 5.5 and gas‐phase proton affinities ranging from 213 to 232 kcal/mol as a method for suppression of signals from alkali‐adducted ions. Stronger bases such as triethylamine and piperidine reduce the signals from bound sodium most effectively, but also decrease the total ion current from oligonucleotide. Imidazole, with a solution pH of ∼8.0, provides modest suppression of sodium/potassium adduct ions, but up to a four‐fold improvement in sensitivity. Co‐addition of imidazole and triethylamine or piperidine produces high ion abundance and good suppression of cation‐adducted species for samples of phosphodiester or phosphorothioate oligomers which have not been desalted via preliminary precipitation or by high‐performance liquid chromatography. Addition of high concentrations of imidazole generates a bimodal distribution of charge states, which may reflect different gas‐phase conformations for single‐stranded oligomers.
Collision‐induced dissociation of C: Effect of energy‐coupling processes on the dissociation dynamics
Authors: Mathur D. , Brink C. , Hvelplund P. , Jensen N. , Yu D. H. 
Published: May 2005

AbstractDissociation of C ions induced in 30 keV collisions with atomic and molecular gases has been studied. The pattern of negativeion formation from C precursors is found to be distinctly different from that obtained for positive‐ion fragments from C precursors in that the collision‐induced dissociation spectrum in the former case is dominated by small negative clusters, presumably of linear geometry, Simple arguments utilizing the relationship of electrostatic properties of different molecular structures to their electron affinities and ionization energies have been invoked to rationalize these observations. The difference in the dissociation dynamics of C and C ions is discussed in terms of competition between different energy‐coupling schemes involving either electronic degrees of freedom or nuclear (vibrational) degrees of freedom.
Application of two‐step laser mass spectrometry to the chemical analysis of aerosol particle surfaces
Authors: Zhan Qiao , Voumard Pierre , Zenobi Renato 
Published: May 2005

AbstractTwo‐step laser mass spectrometry (L2MS) was applied to study the chemical nature of adsorbates on aerosol particles which were collected from different sites, e.g. in the countryside, in an industrial zone, by a downtown road, and in a tunnel. The method combines infrared laser desorption from the particle surfaces followed by ultraviolet laser post‐ionization of the desorbed neutral molecules. Because of the high sensitivity and optical selectivity of L2MS, virtually no sample preparation is needed, and mass spectra can be recorded in a very short time. Qualitative and quantitative comparisons of polycyclic aromatic hydrocarbons in different sampling areas were carried out. By scanning the ionization laser wavelength, two‐dimensional UV/MS spectra can be generated for better identification of the adsorbed species.
A study of protonated molecules of crown ethers containing two thiourea segments by collision‐induced dissociation mass analysed ion kinetic energy spectrometry
Authors: Kralj Bogdan , Timofeev Oleg S. , Žigon Dušan , Kirichenko Tatjana I. , Marsel JožE 
Published: May 2005

AbstractFast atom/ion bombardment mass spectrometry was used to investigate the structures of protonated molecules of macrocyclic nitrogen‐containing crown ethers with two polyoxyethylene chains linked by two thiourea groups. The collision‐induced dissociation (CID) of their MH+ ions, using the mass analysed ion kinetic energy (MIKE) spectrometry method reveals four clearly defined competitive fragmentations. The product‐ion intensities clearly show that, in the MH+ ions of asymmetric crown ethers, the proton is preferentially located in the region of the longer polyoxyethylene chain. The characteristics of CID MIKE spectra of isomeric crown ethers are discussed.
Spin‐coated samples for high resolution matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of large proteins
Authors: Perera Indral K. , Perkins John , Kantartzoglou Stamatina 
Published: May 2005

AbstractThe preparation of near homogeneous samples of large biomolecules, based on the method of spin coating sample substrates, and their use in matrix‐assisted laser/desorption ionization mass spectrometry, for generating spectra with highly reproducible ion signals of analyte molecules with mass extending up to about 150 000 u, are reported. These samples, which could easily be reproduced, consisted of a uniform distribution of matrix/analyte microcrystals over the entire sample surface. Upon laser irradiation, they provided enhanced molecular ion yields and thereby allowed the acquisition of good quality mass spectra over a few (∼1–5) laser pulses. Methods for improving the mass resolution of the molecular ion signals were examined, and a spectrum of bovine insulin obtained from a linear time‐of‐flight instrument with a mass resolution in excess of 1450, together with one of chicken egg lysozyme displaying a resolution of about 450, are presented. The influence of the matrix/analyte molar ratio on the molecular ion yield has also been studied.
Automated liquid chromatography/mass spectrometry for chromatographers
Authors: Pullen Francis S. , Richards Donald S. 
Published: May 2005

AbstractAutomated ‘open access’ mass spectrometry with liquid interfaces is now considered routine in our laboratories at Sandwich, UK. Synthetic chemists log samples into a queue on the mass spectrometer and return a short time later to take the mass spectrum and the sample away. The whole process occurs without any intervention by a mass spectroscopist (D. V. Bowen, M. Dalton, G. Perkins, F. Pullen and D. Richards, Rapid Commun. Mass Spectrom. Vol. 8, p. 632 (1994)). Fast response liquid chromatography/mass spectrometry is a further development in ‘open access’ mass spectrometry driven by the needs of chromatographers, for whom it is important that the identity of each component present in a high‐performance liquid chromatographic separation is known. This Communication describes the development of such a system for our laboratories.
Atomization energy of Au5: Dissociation of stored gold cluster ions
Authors: Kuznetsov Sergei V. 
Published: May 2005

AbstractExperimental data on collision‐induced dissociation of stored gold cluster ions have been interpreted and binding energies have been calculated for small gold clusters Aun(n = 2–5). On the basis of experimental results on the collision‐induced dissociation and photodissociation of gold clusters and the known binding energies for neutral gold dimer and trimer the atomization energy of gold pentamer Au5 has been obtained as 8.7±0.3 eV.
Contribution of mass spectrometry to the determination of basic sites in solid catalysts
Authors: Aramendía María Angeles , Borau Victoriano , Jiménez César , Lafont Fernando , Marinas José María , Porras AndréS , Urbano Francisco José 
Published: May 2005

AbstractThis paper reports a new thermal programmed desorption–mass spectrometry (TPD‐MS) method for determining the number and relative strength distribution of basic sites in solid catalysts using CO2 as titrant. The overall desorbed CO2 area is proportional to the total basicity, while the number of peaks and their maximum temperature (Tmax) are related to the particular type of basic site and its strength. The activation energy for CO2 desorption from various basic sites in each catalyst was calculated via TPD‐MS experiments conducted at a variable heating rate for each catalyst, using the Kissinger equation. Diffuse reflectance infrared analysis of the bands at 2000–1000 cm−1 for CO2 adsorbed on various catalysts allows one to elucidate the nature of the chemical species involved, which depends on the particular type of site. The total basicity results obtained are compared with those provided by an existing spectrophotometric method using benzoic acid (pKa=4.19) as titrant.
Photodissociation of mass‐selected ions in a BEqQ sector mass spectrometer using a pulsed laser
Authors: Aben Ilse , Pinkse Frans A. , Nibbering Nico M. M. , Kistemaker Piet G. 
Published: May 2005

AbstractPhotodissociation of mass‐selected ions in a crossed‐beam setup with a pulsed excimer laser (248 nm) is described. The mass‐to‐charge ratios of the photodissociation products are determined using the mass analyzing quadrupole Q of a hybrid mass spectrometer consisting of a double‐focusing (BE) part followed by two quadrupoles to give BEqQ geometry. Technical aspects of the experiment, as well as experimental results of the photodissociation of the radical cations of toluene, norbornadiene and cycloheptatriene, are presented.
Secondary ion emission from frozen argon by 252Cf fission fragments
Authors: Wien Karl , Spieth Axel 
Published: May 2005

AbstractIn order to study sputtering of Van‐der‐Waals solids by MeV ion impact, films of solid argon condensed onto a metallic substrate at a temperature of 10 K were irradiated by 252Cf fission fragments. The secondary ions emitted from the surface were investigated by a time‐of‐flight technique. The mass spectra are dominated by a cluster series Ar with n ranging from 1 to about 30. Comparatively high absolute ion yields were determined; the yield of Ar+ was 48 ions/impact. The mass line of Ar+ was broadened due to ejection energies of up to 50 eV. The line shape of the cluster ions indicates delayed particle emission. Some of the observed phenomena are not typical for electronic sputtering at MeV energies; they are briefly discussed. These are the first and preliminary results of a systematic exploration of high energy sputtering from solid rare gases.
Recovery of peptides and proteins following matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Cerpa‐Poljak Anne , Jenkins Arthur , Duncan Mark W. 
Published: May 2005

AbstractOnly attomole quantities of polypeptide are consumed during analysis by matrix‐assisted laser desorption/ionization, despite the need to load picomole quantities of these analytes onto the target. By using radioimmunoassay we have demonstrated that the balance of the material (i.e., effectively all that was loaded onto the slide) can be recovered from the target and remains in an immunoreactive form. The bulk of the material, once recovered from the target, can be examined by other analytical techniques including sodium dodecyl sulphate polyacrylamide gel electrophoresis.
Laser desporption Fourier‐transform mass spectrometry of lignins
Authors: Srzić D. , Martinović S. , Tolić Lj. Paša , Kezele N. , Shevchenko S. M. , Klasinc L. 
Published: May 2005

AbstractThe several types of lignin samples (birch, spruce and ‘model’ lignin) were investigated by laser desorption (LD) Fourier‐transform mass spectrometry. In the vapor phase under LD conditions, the investigated lignins prefer to form negative ions of the individual oligomers at well defined mass spacings. Three sequences with Δm=444 confirm the existence of the stable trimer building blocks in the spruce and ‘model’ lignin.
Fast‐Atom bombardment mass spectrometry of the organometallic parasiticide, meglumine antimonate
Authors: Headley J. V. , Yong M. S. , Brooks P. W. , Phillips A. 
Published: May 2005

AbstractThe mass spectrometry of an organometallic parasiticide used for treatment of leishmaniasis was studied using primarily fast‐atom bombardment with complementary studies conducted using electrospray ionization. The positive‐ion mass spectrum of meglumine antimonate contained ions with characteristic antimony isotope ratios (57:43) at m/z 627/629, 507/509, 406/408 and 314/316. There was also evidence of ion clusters containing antimony atoms (Sb1–3), which decompose to the mass 507/509 species under acid pH conditions. For meglumine antimonate, an empirical formula C14H30O10N2Sb (molecular weight 507) is proposed with a structure containing four SbO bonds in a symmetrical geometry.
Secondary ion mass spectrometry measurements of silver isotope ratios in gold‐bearing minerals
Authors: Didenko Petro 
Published: May 2005

AbstractAn ion microprobe unit was used to study silver isotope ratios in gold‐bearing ores. It was found that for ores formed under high‐temperature conditions the light isotope 107Ag is enriched. Low‐temperature deposits are enriched in the heavy isotope 109Ag.
High resolution electrospray mass spectrometry with a magnetic sector instrument: Accurate mass measurement and peptide sequencing
Authors: D'Agostino P. A. , Hancock J. R. , Provost L. R. , Semchuk P. D. , Hodges R. S. 
Published: May 2005

AbstractThe accurate molecular weights for a series of 37 unknown synthetic peptides, used in research studies involving synthetic vaccines, antibacterial peptides or the de novo design of helical peptides and proteins, were determined with a magnetic sector instrument. All data were obtained with external calibration over a wide mass range during magnetic scanning. Errors between observed and theoretical monoisotopic molecular weights were typically in the 5–60 ppm range for the unknowns at sector resolutions between 2500 and 9000 (10% valley). Isotopic clusters for charge states up to 10+ were resolved through the use of high resolution. Collisionally activated dissociation (CAD) in the electrospray interface resulted in product ions that enabled either full or partial sequencing of most unknown peptides of molecular weights below 2000 Da. The complete primary sequence for one peptide was determined and the importance of high resolution was demonstrated by the differentiation of lysine from glutamine, two amino acids differing in residue mass by only 0.0364 Da. Two other peptides, with identical monoisotopic masses, but different primary sequences, were differentiated based on CAD‐MS data.
Chemical ionization mass spectrometry of some nitro‐containing bifunctional aromatic compounds. Location of protonation site
Authors: Tu Ya‐Ping , Lu Kui , Liu Shu‐Ying 
Published: May 2005

AbstractIt is found that the nitro substituent of some aromatic bifunctional compounds shows unusual reactivity towards protonation. In the chemical ionization mass spectra of nitrobenzoic acids and their esters and amides, and of nitrophenols and their ethers, protonations on the carboxyl, ester, amide, hydroxyl or alkoxyl groups are highly suppressed by that on the nitro group. As a result, fragmentations based on protonation on these groups unexpectedly become negligible. Ortho effects were observed for all the ortho isomers where the initial protonation on the nitro group is followed by an intramolecular proton transfer reaction, which leads to the expected ‘normal’ fragmentations. Protonation on the nitro substituent is much more favourable in energy than on any of the other substituents. The interaction of the two substituents through the conjugating benzene ring is found to be responsible for this ‘unfair’ competitive protonation. The electron‐attracting nitro group strongly destabilizes the MH+ ions formed through protonation on the other substituent; although the COR (R  OH, OMe, OEt, NH2) groups are also electron‐withdrawing, their effects are weaker than that of NO2; thus protonation on the latter group produces more‐stable MH+ ions. On the other hand, an electron‐releasing group OR (R  H, Me, Et) stabilizes the nitro‐protonated species; the stronger the electron‐donating effect of this group the more stable the nitro‐protonated ions.
Characterization of underivatized tetrapeptides by negative‐ion fast‐atom bombardment mass spectrometry
Authors: Bradford Adrian M. , Waugh Russell J. , Bowie John H. 
Published: May 2005

AbstractThe [M  H]− ions derived from tetrapeptides generally show two different collision‐induced backbone cleavages which allow the determination of the amino acid sequence of the peptide. The first of these involves the formation of the carboxylate anions of either constituent amino acids or fragment peptides. In the second, amino acids or fragment peptides are eliminated as neutrals. There are a number of residues which undergo characteristic sidechain fragmentations irrespective of their position in the tetrapeptide, e.g. Ser, Thr, Cys, Met, Phe and Tyr. However, there are also some residues which, when situated at the C‐terminal end of the peptide, promote pronounced fragmentation at the C‐terminal position which occurs to the exclusion of the normal backbone cleavages. We conclude that the data obtained from these negative‐ion cleavages are analytically useful, and complement those provided by the cognate positive‐ion technique.
Characterization of oligomers in poly(ethylene terephthalate) by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Weidner St. , Kühn G. , Just U. 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization mass spectrometry was used for the characterization of extracted and synthesized oligo(ethylene terephthalate)s. Generally, cyclic oligomers [GT]n could be found in technical yarns and tiles, whereas our synthesized model oligomers mainly consisted of linear chains H[GT]nG. In addition, some other distributions could be identified as H[GT]nOH and H[GGT]1[GT]n−1G linear oligomers and H[GGT]1[GT]n−1 cyclic oligomers, where G is an ethylene glycol unit, GG is a diethylene glycol unit, caused by impurities of ethylene glycol, and T is a terephthalic acid unit. NMR and IR investigations were carried out to verify these results.
Structural characterization of a new class of penem β‐lactam antibiotics by triple quadrupole tandem mass spectrometry
Authors: Triolo A. , Bonelli F. 
Published: May 2005

AbstractA series of new penem β‐lactam antibiotics, having at position 2 of the thiazoline ring an amido‐substituted amino acid moiety spaced by a methylene group, was analyzed by collisionally activated dissociation (CAD) tandem mass spectrometry on a triple‐quadrupole mass spectrometer, after ionization by cesium ion bombardment. This approach allowed complete structural characterization without any matrix interferences. All the compounds investigated underwent β‐lactam ring cleavage through a typical retro‐Diels–Alder reaction, as well as cleavage of the 2‐side chain at two different points, with charge retention on both sides of the molecule. Subsequent fragmentation reactions essentially involved combinations of the above processes.