bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass and charge assignment for electrospray ions by crown ether adduction
Authors: Cunniff John B. , Vouros Paul , Desiderio Dominic M.
Published: May 2005

The 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

We 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

A 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

Sensitivity 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

A 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

A 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

Gas‐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

The 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

The 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

A 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

Two 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

Despite 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

The 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

On 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

By 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

Electrospray 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

An 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

Stereochemistry 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

A 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

Double 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

A 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

The 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.
Resolution enhancement and parameter estimation in fourier analysis
Authors: Balcou Y.
Published: May 2005

Resolution 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

The 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

Natural 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

A 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

The 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

The 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

The 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

Dissociation 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

Two‐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

Fast 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

The 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

Automated ‘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

Experimental 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

This 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

Photodissociation 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

In 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

Only 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

The 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

The 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

An 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

The 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

It 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

The [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

Matrix‐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

A 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.
Rapid screening of genetic polymorphisms using buccal cell DNA with detection by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Liu Yan‐Hui , Bai Jian , Zhu Yongdong , Liang Xiaoli , Lubman David M. , Siemieniak David , Venta Patrick J.
Published: May 2005

A new approach is developed for the rapid and cost‐effective detection of human genetic polymorphisms based on matrix‐assisted laser description/ionization mass spectrometric (MALDI MS) detection using a nitrocellulose film substrate. This method employs polymerase chain reaction (PCR) amplification using DNA extracted from buccal cells as templates, followed by direct digestion with restriction enzymes and subsequent analysis by MALDI MS. The extraction of DNA from buccal cells provides a rapid and convenient means for sampling PCR‐based diagnostic analysis. The amount of DNA was sufficient as the template for both normal PCR amplifications, and amplifications involving the use of mismatched primers and multiple primers. The MALDI MS methodology has been successfully used for the analysis of such PCR products where restriction fragments generated directly in PCR reactions have been used for detection of carbonic anhydrase and cystic fibrosis transmembrane conductance regulator as model genes. The detection of genetic polymorphisms following routine biological and clinical procedures with the MALDI MS method is demonstrated. The results from MALDI MS analysis are shown to be comparable to those obtained from gel electrophoresis but the MALDI MS method is several orders of magnitude faster than gel electrophoretic techniques. The method described herein should also be readily extended to other areas involving DNA screening and testing.