bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrospray mass spectrometry on a magnetic sector instrument applied to heteropolyacids
Authors: Tuoi Jérémie Le Quan , Muller Etienne 
Published: May 2005

AbstractElectrospray mass spectrometry has been applied to ionic inorganic systems such as heteropolyacids in methanol + water (1/1) or acetonitrile + water (1/1) solutions. Negative‐ion mass spectra were obtained on four different heteropolyacids. Heteropolymolybdates H3PMo12O40 and H4PMo11VO40 and heteropolytungstates H3PW12O40 and H4SiW12O40 gave ions with different charges. H3PMo12O40 gave ions of m/z 1822, 912 and 608 which correspond respectively to [PMo12O + 2H+], [PMo12O + H+]2− and [PMo12O40]3− ions. Resolution of 1:2200 has demonstrated the charge of each ion acquired. Furthermore, the isotope distribution of the observed ions was in good agreement with theory. Thus, electrospray mass spectrometry has become a powerful soft ionization technique for the analysis of such ionic compounds, provided they are soluble and stable in the solvent system used.
Ultramark 1621 as a calibration/reference compound for mass spectrometry. II. Positive‐ and negative‐ion electrospray ionization
Authors: Moini Mehdi 
Published: May 2005

AbstractElectrospray ionization of solutions of Ultramark 1621, a commercially available mixture of fluorinated phosphazenes, in solution of 50:23:23:4 v/v of acetonitrile+water+methanol+acetic acid, produced a series of intense singly charged peaks in the m/z range of 900 to ca. 2200 in both positive‐ and negative‐ionization modes. The chemical compositions and accurate masses of ions in both positive‐ and negative‐ion spectra have been reported. An accuracy of approximately 2 ppm has been achieved for the average molecular weight of bovine insulin using Ultramark 1621 peaks as reference standards.
Mass and charge assignment for electrospray ions by crown ether adduction
Authors: Cunniff John B. , Vouros Paul , Desiderio Dominic M. 
Published: May 2005

AbstractThe introduction of 18‐crown‐6 into the liquid sheath during the electrospray ionization mass spectrometry (ESI‐MS) of peptides leads to the formation of crown ether/peptide complexes. The nominal mass spacing of the peaks from these complexes allows an unambiguous determination of the charge state of the ions and thus of their actual mass. The 264 Da mass shift is much larger than what is achieved by either Na+ or Cu2+ adduction, and is thus potentially more useful for the determination of charge states, especially for multiply charged high‐molecular‐weight species. The addition of an uncharged crown ether does not appear to interfere with the ESI process. Because the crown ether is added to the liquid sheath and not to the original solution, the method should be particularly amenable to chromatographic or electrophoretic techniques because it is essentially a post‐column noncovalent derivatization procedure. Finally, because the complex formation constants are relatively large, the peptide/crown ether complex yields high intensity ions, normally the base peak in the spectrum when analyzing pure peptide samples. Finally, as the crown ether is neutral and noncovalently complexed, a constant‐neutral‐loss scan of their collision‐induced dissociation spectra yields a simplified spectrum that is free of chemical noise.
Detection of 500‐nucleotide DNA by laser desorption mass spectrometry
Authors: Tang K. , Taranenko N. I. , Allman S. L. , Cháng L. Y. , Chen C. H. , Lubman D. M. 
Published: May 2005

AbstractWe report the first detection of DNA segments as large as 500 nucleotides by matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry, using picolinic acid and 3‐hydroxypicolinic acid mixtures as desorption matrices. The successful detection of 500‐nucleotide DNA indicates that laser mass spectrometry is now emerging as a new biotechnology tool for DNA‐related research. It should be possible to utilize fast detection of large DNA segments by laser mass spectrometry for rapid human genome sequencing.
Peptide ladder sequencing by mass spectrometry using a novel, volatile degradation reagent
Authors: Bartlet‐Jones Michael , Jeffery William A. , Hansen Hans F. , Pappin Darryl J. C. , Cottrell John 
Published: May 2005

AbstractA conceptually novel approach to protein sequencing involves the generation of ragged‐end polypeptide chains followed by mass spectroscopic analysis of the resulting nested set of fragments. We report here on the synthesis and development of a volatile isothiocyanate (trifluoroethylisothiocyanate) that allows the identification of several consecutive residues starting with a few picomoles of peptide. The nested set of peptides is generated simply by adding equal aliquots of starting peptide each cycle and driving both the coupling and cleavage reactions to completion. No additional reagents are required to act as chain terminators and retention of the peptide terminal amine allows for subsequent modification with quaternary ammonium alkyl NHS esters to improve sensitivity. Complex washing procedures are not required each cycle, as reagents and by‐products are efficiently removed under vacuum, eliminating extractive loss. Multiple peptide samples can be processed simultaneously, with each degradation cycle completed in 35–40 min. The inherent simplicity of the process should allow for easy automation and permit rapid processing of samples in parallel.
Detection limits for matrix‐assisted laser desorption of polypeptides with an external ion source Fourier‐transform mass spectrometer
Authors: Li Yunzhi , McIver Robert T. , Chait Brian T. 
Published: May 2005

AbstractSensitivity in the low‐femtomole range with mass resolution greater than 20 000 is demonstrated for several polypeptides analyzed by a mass spectrometer that pairs matrix‐assisted laser desorption/ionization (MALDI) and Fourier‐transform mass spectrometry (FTMS). The compounds investigated were substance P, renin substrate, melittin, the B‐chain of bovine insulin, and bovine insulin. Standard solutions of the polypeptides were prepared with 30% acetonitrile + water, and micropipettes were used to transfer small amounts (1–20 fmol) to a sample probe. The samples were embedded in a large excess of matrix material (2,5‐dihydroxybenzoic acid) and ionized by a pulse from an excimer laser. The FTMS instrument used for these experiments has the MALDI source in a separate chamber outside the magnetic field. Ions are extracted from the source and transported by an RF‐only quadrupole ion guide to an FTMS analyzer cell mounted in the homogeneous region of a 6.5 T superconducting magnet. The high sensitivity of MALDI‐FTMS is due, in part, to the high transfer efficiency of the ion guide, even for ions with a wide range of kinetic energies. The ion guide is easy to use because there are only two adjustments (RF amplitude and DC offset voltage), and unlike electrostatic ion transport means, alignment of it with the axis of the magnetic field is not critical. The mass resolution and sensitivity of MALDI‐FTMS is compared with that of MALDI done with time‐of‐flight, magnetic sector, and quadrupole iontrap mass spectrometers.
A PC‐based integrating data acquisition system
Authors: Sägesser Martin , Friedli Felix , Schlunegger Urs Peter 
Published: May 2005

AbstractA data acquisition system for mass spectrometers has been developed based on an IBM PC plug‐in board equipped with a TMS320C25 processor. The processing unit, programmed in Assembler language, acquires analog signals from the detector of a mass spectrometer and converts it into an array of digital data. The communication software, written in Pascal language, controls the processor, handles the spectra and stores the data. The system requirements and its properties are discussed and some applications are shown.
Linear mass calibration in the quadrupole ion‐trap mass spectrometer
Authors: Doroshenko Vladimir M. , Cotter Robert J. , Lubman D. M. 
Published: May 2005

AbstractA new method of operation of the quadrupole ion‐trap mass spectrometer in the resonance ejection mode is introduced, that enables one to obtain accurate, linear mass calibration. The method employs linear modulation of the excitation voltage applied to the end‐caps while scanning the RF trapping field on the ring electrode. Calibration lines can be defined by a single calibration point because they converge near the reference point where the mass and trapping voltage are equal to zero. Mass assignment accuracy is achieved which is within, or of the order of, errors usually associated with the space‐charge effect. The method was implemented on a modified ion‐trap detector for ions formed by matrix‐assisted laser desorption, but can be used with other ionization techniques and applied to both external and internal calibration routines.
Gas‐phase basicities and proton affinities of lysine and histidine measured from the dissociation of proton‐bound dimers
Authors: Wu Zhuchun , Fenselau Catherine , Graham Cooks R. 
Published: May 2005

AbstractGas‐phase basicities and proton affinities of lysine and histidine were measured by the kinetic method. Using low‐energy collisional activation to change the effective temperature in the dissociation of proton‐bound dimer, proton affinities of lysine and histidine were determined to be 235.3 and 234.0 kcal/mol respectively. A large entropy effect was found for lysine, and thus at temperatures above 300 K, histidine is slightly more basic than lysine. Peptides that contain lysine or histidine are more basic than lysine or histidine. The basicities of these peptides depend on their structures and the internal hydrogen bonding.
A curved field reflectron time‐of‐flight mass spectrometer for the simultaneous focusing of metastable product ions
Authors: Cornish Timothy J. , Cotter Robert J. , Todd Peter J. 
Published: May 2005

AbstractThe ability to simultaneously focus a wide mass range of metastable fragment ions formed after the initial ionization event in a matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometer has been made possible by the development of a new type of ion reflector. This coaxially designed time‐of‐flight instrument employs a modified single stage reflector whose axial voltage gradient rises differentially in order to produce an alignment of energy focal points for product ions. In contrast, product‐ion focusing in conventional constant field reflectors occurs over a broad range of distances from the reflectron exit. Approximately 90% of the product‐ion mass spectrum can be collected without adjustment, thereby eliminating the need to scan the reflector voltage. Design considerations of the curved field reflectron, its calibration properties and representative metastable spectra of several peptides are discussed.
Collision energy effects on the collision‐induced dissociation of multiply charged melittin
Authors: Fabris Daniele , Kelly Michele , Wu Zhuchun , Fenselau Catherine , Jennings K. R. 
Published: May 2005

AbstractThe fragmentation of the inelittin 4+ ion has been studied over a range of collision energies from 28 eV to 12 keV in a four‐sector mass spectrometer. Patterns of fragmentation and energy conversion were found to be analogous to those observed for singly charged peptides. High numbers of collisions were not required for activation at low energies.
Charge‐remote fragmentation of peptides derivatized with 4‐aminonaphthalenesulphonic acid
Authors: Lindh Ingemar , Griffiths William J. , Bergman Tomas , Sjövall Jan 
Published: May 2005

AbstractA series of small peptides has been studied by negative‐ion fast‐atom bombardment mass spectrometry with collision‐induced dissociation. It has been found that by derivatizing peptides with 4‐aminonaphthalenesulphonic acid in a peptide linkage at the C‐terminus, negative‐ion formation can be enhanced and fragmentation in collision‐induced dissociation reactions controlled. The peptide‐naphthalenesulphonates show charge‐remote fragmentations and the resultant spectra give sequence information.
Characterization of kerogens by matrix‐assisted laser desorption ionization mass spectroscopy
Authors: Li Chun‐Zhu , Herod Alan A. , John Phillip , Johnson Chris A. F. , Parker John E. , Smith Gerry P. , Humphrey Paul , Chapman John R. , Rahman Mukhlis , Kinghorn Robert R. F. , Kandiyoti Rafael , Games D. E. 
Published: May 2005

AbstractTwo kerogen samples from shales of different geological age, selected from each of Types I, II and III, have been characterized by matrix‐assisted laser desorption ionization mass spectroscopy (MALDI‐MS). A Kratos Kompact MALDI III time‐of‐flight mass spectrometer equipped with a nitrogen laser operated at 337 nm was used on samples mounted in a matrix of sinapinic acid. The spectrometer was used in linear mode with a mass range up to 270 000 u and an ion extraction voltage of 20 kV. Individual spectra from 50 laser shots at low laser fluence were summed for each spectrum. The present study is a first attempt at characterizing kerogens by MALDI‐MS. At low mass (200–500 u) families of peaks consisting of overlapping homologous series of apparently polar compounds have been observed: these peaks appear to be distinct from those due to the matrix material. In higher mass regions of the spectra, continua of masses extending from 1000 u up to around 10 000 u were observed; ions at higher masses were separated to baseline up to masses of 50 000 u. Evidence was found for a relationship between the minimum laser power sufficient for activating the MALDI‐ionization process and the geological age of the kerogens; the laser power decreased as the geological age increased. In the case of one kerogen, a high laser fluence was used to generate molecular ions up to the detection limit of the mass spectrometer, in excess of 260 000 u. This paper presents results from a preliminary study of kerogens which requires an in‐depth examination of the desorption process in complex mixtures.
Formation of atomic hydrogen in matrix‐assisted laser desorption ionization
Authors: Scott C. T. J. , Kosmidis C. , Jia W. J. , Ledingham K. W. D. , Singhal R. P. 
Published: May 2005

AbstractDespite the widespread use of matrix‐assisted laser desorption ionization, the processes involved in ion formation have yet to be satisfactorily explained. Several protonation processes have been suggested as possible methods for the creation of the analyte ions. In this work the existence of neutral hydrogen atoms in the ablation plume is reported. These are selectively ionized from the ground state through a (2+1) multiphoton resonant excitation scheme. The mass spectra at different delay times between the ablation and the post‐ablation‐ionization lasers have demonstrated the existence of hydrogen atoms with high velocities in the ablated plume.
Conjugation reactions of cyclodepsipeptide to glutathionyl adducts by direct ‘in‐beam’ synthesis under negative‐ion fast‐atom bombardment conditions
Authors: Loutelier C. , Cherton J.‐C. , Lange C. 
Published: May 2005

AbstractThe conjugation products of E‐destruxin (cyclodepsipeptide) with glutathione have been identified by fast‐atom bombardment mass spectrometry. Appropriate conditions were developed for cyclodepsipeptide substrate, which enabled the direct, dynamic mass spectra analysis of spontaneous as well as glutathione‐s‐transferase catalyzed conjugation reactions. Application to the most active cyclopeptide in the series of destruxins yielded glutathionyl adduct.
A potential problem in the analysis of toxaphene by electron‐capture negative‐ion mass spectrometry
Authors: Lau Benjamin P.‐Y. , Weber Dorcas , Andrews Paul 
Published: May 2005

AbstractOn analyzing 11 pure individual toxaphene congeners, it was noted that a nonachloro congener (2,2,5,5,8,8,9,10,10‐nonachlorobornane, Parlar's No. 62) failed to produce a reasonable [M–Cl]− response under our electron‐capture negative‐ion (ECNI) chemical ionization conditions. On the other hand, this congener gave a stronger response than other nonachlorobornane congeners in electron impact (EI) mode. Based on EI mass spectra data as well as electron capture gas chromatographic results, this congener is one of the major components in commercial toxaphene and is also present in fish and cod liver oil samples. This congener‐specific discriminatory effect raises concern about possible false negative results from the ECNI/selective‐ion monitoring analyses.
Improving the resolution of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry by exploiting the correlation between ion position and velocity
Authors: Colby Steven M. , King Timothy B. , Reilly James P. , Lubman D. M. 
Published: May 2005

AbstractBy taking into account the correlation between the positions and velocities of desorbed ions in the source region of a time‐of‐flight mass spectrometer and by including this relationship in the equations used to determine spacefocusing conditions, it is predicted that matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectral resolution can be improved significantly. Experiments involving MALDI of two proteins, insulin and ubiquitin, demonstrate the validity of this concept. Adduct formation does not limit mass spectral resolution in these two cases.
Characterization by electrospray tandem mass spectrometry of a novel series of synthetic difuranic diamine dihydrochlorides containing the bis(5‐aminomethyl‐2‐furyl) unit
Authors: Gentil Emmanuel , Lesimple Alain , Bigot Yves Le , Delmas Michel , Banoub Joseph 
Published: May 2005

AbstractElectrospray mass spectrometry has aided the structural characterization and differentiation of a novel series of synthetic difuranic diamine hydrochlorides. As expected, these compounds generally afforded the protonated molecules minus two molecules of HCI to yield the abundant [M + H − 2HCI]+ pseudomolecular ions, which are equivalent to the [M + H]+ ions obtained from the corresponding free difuranic diamine compounds. Possible fragmentation routes were first obtained by controlled collisionally activated dissociation (CAD) initiated by cone‐voltage fragmentation. Low‐energy CAD tandem mass spectrometric analyses of the [M + H − 2HCI]+ ions confirmed the characteristic fingerprint patterns obtained by cone‐voltage fragmentation for all the difuranic diamine compounds investigated. MS/MS product‐ion spectra of selected intermediate fragments provided additional structural data and confirmed the fragmentation routes of their precursor ions. Electrospray mass spectrometry has been proven to be a specific and very sensitive method for detection and characterization of these novel difuranic diamine hydrochlorides.
C60‐assisted laser desorption/ionization mass spectrometry in the analysis of phosphotungstic acid
Authors: Hopwood Femia G. , Michalak Leszek , Alderdice David S. , Fisher Keith J. , Willett Gary D. 
Published: May 2005

AbstractAn application of C60‐assisted laser desorption/ionization mass spectrometry to a heteropoly inorganic system: phosphotungstic acid, H3PO4(WO3)12, is presented. A nitrogen laser (337 nm) on a linear tandem time‐of‐flight mass spectrometer is used for the observation of the laser‐power dependence of mass spectra of this material.
Ion/molecule reactions in the gas phase: Comparison of the enantioselectivity of two chiral gases
Authors: Sellier Nicole M. , Bouillet Christine T. , Douay David L. , Tabet Jean‐Claude E. 
Published: May 2005

AbstractStereochemistry study has always been a very important subject, but the determination of chirality has become potentially possible with the emergence of chemical ionization. In this study, mass spectrometry and tandem mass spectrometry (MS/MS) were used as a tool for distinguishing the isomers of (+) and (−) isopinocampheols and (+) and (−) menthols by ion/molecule reaction in the gas phase using two different chiral gases, G. The reactive plasma is made up of the ion GH+. Interactions between the plasma and the isomer M of (+) and (−) isopinocampheols and (+) and (−) menthols lead to the formation of the ions [M‐M2O+H]+, [M‐H2O+GH]+, [M+GH]+ and [2M+H]+. In mass spectrometric analysis, their relative intensities differ because of the absolute configuration of M. In MS/MS the relative intensities of the daughter ions of [M‐H2O+GH]+ ions enable a positive determination of (+) and (−) isomers. The susbtitution ion [M‐H2O+GH]+ arises via an SN2 pathway that is regioselective and sterospecific.
Peptide sequencing by partial acid hydrolysis and high resolution plasma desorption mass spectrometry
Authors: Zubarev R. A. , Chivanov V. D. , Håkansson P. , Sundqvist B. U. R. , Ens Werner 
Published: May 2005

AbstractA method of deriving peptide sequence information using partial acid hydrolysis in combination with accurate mass measurements and immonium ion analysis provided by high‐resolution plasma desorption mass spectrometry has been developed. The technique is very simple in terms of the chemistry and involves a short‐time (3–30 min) incubation of the peptide in 1N–6N HCl at 100–110°C with subsequent mass spectrometric analysis. Partial acid hydrolysis is found to produce sequence‐specific segments, often ladder‐like, although not always a complete set. Two application examples of the method are given: the linear peptide bradykinin and desmopressin, a peptide with an internal SS bond and a non‐amino‐acid constituent. The technique has proved to be particularly useful in cases where some a priori information on the peptide structure was already known or where the automated Edman degradation technique might yield erratic results or not work at all.
Calculated and measured double‐ionization energies of 1,1‐dimethyl allene to triplet electronic states of the dication
Authors: Andrews Stuart R. , Parry David E. , Harris Frank M. 
Published: May 2005

AbstractDouble ionization of the 1,1‐dimethyl allene molecule to triplet electronic states of the dication has been studied using theoretical and experimental methods. Although the calculated data indicate a high density of states, suitable groupings of calculated double‐ionization energies to those states agree well with values measured by double‐charge‐transfer spectroscopy. This indicates that the theoretical predictions provide an accurate indication of the composition of the triplet‐state manifold for the 1,1‐dimethyl allene dication between 25.2 eV and 39.6 eV.
Monomer mapping: A PC‐based software tool facilitating the determination of monomer compositions from mass spectrometric molecular weight data
Authors: van Setten Dirk C. , van de Werken Gerrit , Jacobs P. L. 
Published: May 2005

AbstractA method has been developed to establish the monomer composition of (bio)macromolecules. The method, which we call monomer mapping, involves mass spectrometry and a computer program. Given the (nominal) m/z value of the molecular ion as well as the elemental compositions of all monomeric residues possibly present, the computer program generates all fitting monomer compositions and their corresponding m/z ratios. The determination of the monomer composition is enabled by verification of the presence of a signal at the calculated m/z ratios for the individual monomers, using high resolving power mass spectrometry. Monomer mapping can be used to determine monomer compositions of individual components in mixtures without applying (chromatographic) separation techniques. The scope of monomer mapping has been enlarged by combining it with the results of per‐O‐methylation, which gives information on the number of exchangeable hydrogens. The results of, for instance, amino acid analysis could also be included in the program. Monomer mapping has been successfully applied to determine the glycosyl compositions of saponins.
Positive‐ion fast‐atom bombardment tandem mass spectrometry of peptide nucleic acids
Authors: Takao Toshifumi , Fukuda Hiroyuki , Coull James , Shimonishi Yasutsugu 
Published: May 2005

AbstractThe base sequence of synthetic peptide nucleic acids (PNAs), novel antisense agents, was analyzed by positive‐ion fast‐atom bombardment tandem mass spectrometry (FAB‐MS/MS). Upon high‐energy collisional activation decomposition, PNA oligomers provided apparent MS/MS product ions resulting from specific cleavage along the PNA backbone.