bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrospray mass spectrometry of Malayan pit viper (Calloselasma rhodostoma) venom
Authors: Sweetman G. M. A. , Garner G. V. , Gordon D. B. , Tetler L. , Theakston R. D. G.
Published: May 2005

A high‐performance liquid chromatography protocol has been developed for the analysis of snake venoms. This system has been used to isolate eight fractions from Malayan pit viper (Calloselasma rhodostoma) venon. The fractions have been analysed using electrospray mass spectrometry. A number of major components were found with masses ranging from 13670 to 22750 Da.
The application of ‘MaxEnt’ to high resolution mass spectrometry
Authors: Ferroge A. G. , Seddon M. J. , Skilling J. , Ordsmith N.
Published: May 2005

The MaxEnt technique has premviously been successfully applied to the deconvolution of electrossppray mass spectra. The latest version of the Cambridge University software, ‘MemSys5’, has now been applied to high resolution mass spectra. Initial results have shown that peaks requiring an instrument resolution of almost 200 000 to separate them are readily resolved by MaxEnt on data acquired at a resolution of only 50, 000. Moreover, the MaxEnt results are accompanied by quantitative and realistic error bars.
A new reduction process in fast‐atom bombardment mass spectrometry: Substitution of a nitro group by a hydrogen
Authors: Aubagnac J.‐L. , Gilles I. , Astier R. , Gosselin G. , Imbach J. L. , Bergogne M. C.
Published: May 2005

A new example of the resuction phenomenon often observed in fast‐atom bombardment mass spectrometry is described, involving the substitution of a nitro function by a hydrogen atom. This reaction, clearly visible with glycerol as metrix, takes place to only a very limited extent with m‐nitrobenzylalcohol.
Three‐dimensional deconvolution of multiply charged spectra
Authors: Labowsky Michael , Whitehouse Crag , Fenn John B.
Published: May 2005

A three‐dimensional surface of signal vs molecular weight and adduct ion mass (H+, Na+, NH+ 3, etc) is introduced as an analysis tool for determining the mass of higher‐molecular‐weight compounds from their representations as a series of multiply charged peaks in a mass spectrum produced by electrospray ionization. This three‐dimensional approach has distinct advantages over conventional two‐dimensional analysis techniques with regard to detecting errors in the mass scale calibration, assessing the confidence level of a deconvoluted molecular‐weight assignment and in analyzing complex multiply charged spectra of mixtures. Special techniques are introduced which allow analysis of multiply charged spectra; containing adduct ion mixtures. solvent molecules absorbed on the parent molecule and ‘peaks’ resulting from partial dissociation of the parent molecule.
ortho‐Rearrangements of o‐alkylphenoxide anions
Authors: Reeks Lachlan B. , Eichinger Peter C. H. , Bowie John H.
Published: May 2005

The collision‐induced mass spectra of the o‐methyl and o‐ethylphenoxide anions show loss of formaldehyde and acetaldehyde, respectively. These processes are rationalized in terms of a reversible rearrangement o‐RC6H4O− ⇌ [(C6H4)−OR] (R = alkyl).
Species‐selectivity effects in the production of electrospray ions
Authors: Hiraoka Kenzo , Murata Konosuke , Kudaka Ichiro
Published: May 2005

Positive‐ and negative‐ion production from electrosprayed charged liquid droplets has been studied. For acidified solutions of arginine, Arg‐Arg‐Arg, Lys‐Lys, and (CH3)4NBr in methanol + water (80/20, v/v), the relative intensities of CH3OH2+ ions were found to decrease faster than those of other sample ions as the distance (d) between the capillary tip and the interface plate was increased. The radial distribution of ion intensities in the spray cone was also examined. While the CH3OH2+ ions and multiply charged ions had maximum intensities in the central region of the spray cone, NH4+ and singly charged oligopeptide ions were found to be distributed in its peripheral region. The observed species‐selectivity effects in the production of electrospray ions were interpreted in terms of the volatility of ions in the charged liquid droplets. The negative‐ion intensities of the oligopeptide Glu‐Glu were enhanced greatly when ammonia was added to the solution. An optimum ammonia concentration which gives the strongest negative‐ion signals was ∼10−4M.
Pyrolysis/gas chromatography/mass spectrometry and Fourier‐transform infrared spectroscopy of amber
Authors: Galletti Guido C. , Mazzeo Rocco
Published: May 2005

Amber samples from archaeological objects belonging to the collection of the Museo Civico Archeologico of Bologna were analysed by pyrolysis/gas chromatography/(ion‐trap) mass spectrometry (PY/GC/MS) and Fourier‐transform infrared spectroscopy (FTIR) to assess the geographic origin of the fossil resin. Both techniques showed potential in the study of amber, because they require small sample amounts, virtually no sample preparation and provide a fingerprint which is highly diagnostic of the material under investigation. Typical pyrograms, mass spectra and FTIR spectra are shown and compared to those obtained from standard amber of known geographical origin. The usefulness of composite mass spectra, namely mass spectra obtained by summing all or part of the mass spectra acquired within the pyrogram, to create a library of PY/GC/MS data and to compare samples is evaluated.
Pyrolysis/gas chromatography/ion‐trap mass spectrometry of the ‘tooth brush’ tree (Salvadora persica L.)
Authors: Galletti Guido C. , Chiavari Giuseppe , Kahie Yassin Duale
Published: May 2005

Chemical characterization of ‘tooth brush’ tree (Salvadora persica L.) sticks was carried out using a pyrolysis/ gas chromatograph coupled to an ion‐trap detector mass spectrometer. Electron impact and chemical ionization mass spectra, along with chromatographic profiles obtained by both flame ionization and nitrogen/phosphorous detectors, enabled the structure of some eighty pyrolysis fragments to be proposed. These were mainly lignin and polysaccharide derivatives of phenolic and furanic natures, respectively. However, compared with the pyro‐grams of other well‐studied lignocellulosic materials, S. persica showed several unique nitrogen‐containing compounds, some of which were tentatively identified as pyrrolidine, pyrrole and piperidine derivatives on the basis of their mass spectra and chromatographic elution order.
Investigation of some steroids by means of thermospray and tandem mass spectrometry
Authors: Curcuruto O. , Franchi D. , Hamdan M. , Favretto D. , Traldi P.
Published: May 2005

The detection limits of a number of steroids have been determined by means of loop‐injection thermospray (TS) mass spectrometry. The measured limits were found to be in the range 1 pg‐1O ng/μL. Combined positive‐ion TS/tandem mass spectrometry yielded clear qualitative differences between mass selected protonatcd testosterone and estriol ions, both of which have the same nominal molecular weight. These differences are necessary for the correct identification of either species which may be present within a complex mixture. The heights of the peaks due to the two competing reaction channels, [M + H]+ and [M + NH4]+, were monitored as a function of the repeller voltage in the range 100‐350 V, and the implications of the acquired data are discussed.
Studies on the interaction of elfamycin antibiotics with elongation factor‐Tu by mass spectroscopic techniques
Authors: Sottani C. , Islam K. , Soffientini A. , Zerilli L. F. , Seraglia R.
Published: May 2005

Elfamycin antibiotics have been studied by mass spectrometry, using direct‐liquid‐introduction chemical ionization and fast‐atom bombardment (FAB), but these techniques are not suitable for the identification of the interaction product between antibiotic and elongation factor‐Tu (EF‐Tu). A new mass spectrometric technique, matrix‐assisted laser desorption (MALD), has been employed to clearly identify the complex formed between EF‐Tu and kirromycin. Using MALD operated in the positive‐ion mode, molecular weight values of 43 330 and 44 234 Da were obtained for EF‐Tu and the adduct EF‐Tu/kirromycin, respectively; both are close to the theoretically calculated values of 43 225 and 44 060. These measurements suggest that MALD techniques can be used to obtain useful information on EF‐Tu/elfamicyn antibiotic interaction. Other techniques, such as desorption chemical ionization, FAB and thermospray have been used to obtain information on the fragmen‐tation patterns of some elfamycins (kirrotmycin, aurodox, efrotomycin). In particular, the positive‐ion FAB spectrum of efrotomycin obtained by using a matrix of glycerol and water containing K+ ions, contained the quasimolecular ion [M + K]+ at m/z 1184. Thermospray appeared to be the best technique for structural elucidation studies. In fact, positive‐ion spectra of kirromycin, aurodix and efrotomycin are characterized by significant fragmentation ions, while molecular ions are of very low intensity.
Pyrolysis/gas chromatography/mass spectrometry in the analysis of asphaltenes
Authors: Nali M. , Corana F. , Montanari L.
Published: May 2005

A study on the flash pyrolysis of asphaltenes using gas chromatography/mass spectrometry is reported. Six n‐heptane‐precipitated asphaltene samples, characterized by elemental analysis and nuclear magnetic resonance (NMR), were selected because of their different compositions. By considering the main pyrolysis products some structural parameters were worked out. The results obtained from the pyrolysis data were compared to those deriving from elemental analysis and NMR. In spite of the severe thermal treatment (650°C for 20 s) undergone by the asphaltenes, the pyrolysis products qualitatively reflect structural differences shown in the original samples by NMR (a non‐destructive technique).
Analysis of microcystins from cyanobacteria by liquid chromatography with mass spectrometry using atmospheric‐pressure ionization
Authors: Edwards Christine , Lawton Linda A. , Beattie Kenneth A. , Codd Geoffrey A. , Pleasance Stephen , Dear Gordon J.
Published: May 2005

A combined liquid chromatographic mass spectrometric method was developed for the analysis of microcystins (hepatotoxic cyclic heptapeptides) produced by cyanobacteria (blue‐green algae). The method was used to confirm the identity of microcystins, tentatively identified by high‐performance liquid chromatography using diode‐array detection, in extracts from natural‐bloom material and a sample of river water where hepatotoxic cyanobacteria were present. The potential of tandem mass spectrometry for obtaining structural information and providing a selective screen for these compounds was also investigated.
Gas‐phase reactivity of ambident thio‐enolate and oximate anions
Authors: Freriks Ivo L. , de Koning Leo J. , Nibbering Nico M. M.
Published: May 2005

The gas‐phase chemical behaviour of ambident thio‐enolate anions from thioacetaldehyde and oximate anions from acetaldoxime and acetone oxime has been studied using the method of Fourier‐transform ion cyclotron resonance mass spectrometry. It appears that the thio‐enolate anions, generated by an efficient base‐induced E2 elimination of ethene from ethyl vinyl sulfide, exhibit a strong preference for addition via the sulfur rather than via the carbon nucleophilic center in the reactions with a series of unsaturated polyfluorocarbon compounds. This preferred addition via the sulfur nubleophilic center is considered to be promoted both by specific frontier orbital and by electgrostatic interactions between the reactants. Further, acetaldoxime and acetone oximate anions exclusively react via the oxygen nucleophilic center with the series of unsaturated polyfluorocarbon compounds. Electrostatic interactions are held responsible for the reaction selectivity of the oximate anions. This is in contrast with the corresponding enolate anions, for which it is considered that the previously studied ambident chemical behaviour is governed by specific frontier orbital interactions.
Gas‐phase chemistry of metal carbonyl anions: Reactions of Fe(CO) with methanol and its 13C‐, D‐ and 18O‐labelled analogues studied by fourier‐transform ion cyclotron resonance mass spectrometry
Authors: van den Berg K. J. , Ingemann S. , Nibbering N. M. M. , Gregor I. K.
Published: May 2005

The reactions of the metal dicarbonyl anion Fe(CO) with methanol and five of its isotopomers, namely CD3OH, CH3OD, CD3OH and CH318OH have been studied by the use of Fourier‐transform ion cyclotron resonance mass spectrometry. Three competitive reaction channels have been identified in these trapped‐ion/molecule studies which, for methanol, lead to the formation of three primary reaction products, namely [HFe(CO)(OCH)3]− formed in a decarbonylation channel; Fe(CO) in a channel involving CH and OH bond activations and bis‐dehydrogenation of a collision complex; and also [(CH2O)Fe(CO)2]− in a separate channel involving the elimination of a single H2 molecule. The primary product ion [HFe(CO)(OCH)3]− further reacts with methanol to give a bis‐alkoxy substituted metal carbonyl ion [(CH3O)2Fe(CO)]− at trapping times of several seconds. Complex deuterium isotope effects of an interactive nature with respect to the three reaction channels also have been observed.
Enhancement of resolution in matrix‐assisted laser desorption using an ion‐trap storage/reflectron time‐of‐flight mass spectrometer
Authors: Chien Benjamin M. , Michael Steven M. , Lubman David M.
Published: May 2005

A quadrupole ion‐trap storage/reflectron time‐of‐flight mass spectrometer (IT/RETOFMS) has been used to enhance resolution in the ultraviolet matrix‐assisted laser desorption/ionization (MALDI) of peptides. The MALDI of peptides is performed directly inside an ion‐trap storage device using 266 nm laser radiation from a 2,5‐dihydroxybenzoic acid matrix. Helium buffer gas is used to collisionally cool the hot desorbed ions and to rapidly relax the ions to the center of the ion trap. The result is that upon ejection into the TOF device, a resolution of nearly 6200 is obtained‐for Substance P using a 90 ms storage time. A resolution of 3000–6000 is consistently obtained for peptides up to 2100 u used in this study. The individual ion peaks from the isotopic distribution are easily resolved under these conditions. In addition, the ion trap is found to be useful as an ion‐storage device for enhancing the signal where multiple laser desorption pulses can be stored per cycle in the trap before ejection into the RETOF. Also, using the relatively high resolving power of the IT/RETOF instrument, excellent mass accuracy can be obtained using the matrix background and bradykinin as internal standards.
The analysis of mock DNA sequencing reactions using matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Fitzgerald Michael C. , Zhu Lin , Smith Lloyd M.
Published: May 2005

A mock sequencing experiment is described in which matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry is used to analyze mixtures of synthetic oligodeoxynucleotides chosen to match the first 24 DNA fragments generated in typical sequencing reactions using a standard M13mp19 template and primer. The experiments permitted the evaluation of important issues relating to resolution, sensitivity, multiple charging, and adduct formation. Mass resolutions (full width at half maximum) were between 100 and 200, and it was relatively straightforward to assign bases in the sequencing simulation using subpicomolar quantities of material. These results demonstrate the potential of MALDI mass spectrometry in DNA sequence analysis.
Quantitative applications of matrix‐assisted laser desorption/ionization with time‐of‐flight mass spectrometry: Determination of copolymer composition in bacterial copolyesters
Authors: Abate R. , Ballistreri A. , Montaudo G. , Garozzo D. , Impallomeni G. , Critchley G. , Tanaka K.
Published: May 2005

Poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) of microbial origin has been analyzed by matrix‐assisted laser desorption/ionization (MALDI) in a time‐of‐flight mass spectrometer, after partial methanolysis, using two different instruments, Our results show that the mass spectral intensities recorded in the MALDI mode correlate with previously reported fast‐atom bombardment and direct chemical ionization data. MALDI compares favourably with these other two techniques in that it is more suitable to the analysis of complex mixtures and of higher molecular masses.
Automated routine thermospray mass spectrometry in the analysis of potential drug compounds
Authors: Tiller Philip R. , Lane Stephen J.
Published: May 2005

A System to automate the analysis of routine mass spectrometry samples, using either a thermospray or particle‐beam interface, has been developed. This has allowed unattended operation and has freed expert mass spectrometrists to address ‘real’ problems. The system also acts as a filter to the problem‐solving service.
Complete third‐order resolution formulae for time‐of‐flight mass spectrometers incorporating reflectrons
Authors: Ioanoviciu D.
Published: May 2005

The resolution of single‐ and double‐stage, homogeneous electric mirror time‐of‐flight mass spectrometers can be calculated with the derived formulae for detectors located normally to the ion flight direction or parallel to the mirror face. These formulae account for contributions to the peak width from ion initial velocity and position in the source (‘turn around’ time included), from ion‐packet longitudinal and transverse size at the source final grid, as well as due to the angular ion spread. Third‐order terms are included for beam size, angular aperture and velocity spread, the incidence angle being small. The field‐free space needed to obtain energy focusing in time is connected with the length of the accelerating space inside the source.
Photofragmentation in Fourier‐transform ion cyclotron resonance: Use or misuse?
Authors: Gäumann Tino , Zhao Guohong , Zhu Zhiqing
Published: May 2005

The noise in a sector or quadrupele mass spectrometer is determined by the source, i.e. the number of ions present in the signal, whereas in Fourier‐transform ion cyclotron resonance it is detector limited. In addition, the Fourier transform spreads white noise equally over the whole spectrum. Thus the accuracy for broad‐band spectra is generally rather low. However, the precision, i.e. the reproducibility of successive spectra, is astonishingly high. This fact has been used with much success, for example in collisionally activated dissociation in Hadamard spectra. It is shown that photofragmentation spectra are also very reproducible and thus allow—at least in principle—a ‘kinetic deconvolution’ of a series of such spectra. In such a case, nonlinear regression has to be applied to the data. Since in most kinetics problems several exponential functions are involved, and since it is well known that these exponential functions are notoriously difficult to approximate with a Marquardt‐Levenberg algorithm, the validity of the results may be questionable. Three examples (protonated benzene, cycloheptatriene, deuterated toluene) are chosen to demonstrate some of the difficulties and pitfalls of the procedure.
Excitation and detection geometries for Fourier‐transform mass spectometry
Authors: Schweikhard Lutz
Published: May 2005

A short overview of current excitation and detection techniques for Fourier‐transform mass spectrometry and related ion cyclotron resonance experiments is given, and some ideas are discussed which may lead to new developments.
Mass measurement accuracy of matrix‐assisted laser desorbed biomolecules: A Fourier‐transform ion cyclotron resonance mass spectrometry study
Authors: Solouki Touradj , Gillig Kent J. , Russell David H.
Published: May 2005

The use of binary matrices and internal calibrants to improve the mass measurement accuracy in matrix‐assisted laser desorption ionization (MALDI) with Fourier‐transform ion cyclotron resonance (FTICR) mass spectro‐metry is described. Binary matrices enhance the analyte ion yield and enable a complete MALDI‐FTICR mass spectrum to be obtained from a single laser shot. The advantage of single‐laser‐shot data acquisition is that it eliminates line‐broadening due to shot‐to‐shot frequency variations. It is shown that unresolved product ions, mainly due to loss of H2O and/or NH3, shift the centroid of an unresolved multi‐component peak. A mass measurement accuracy of 12 ppm was obtained for the bovine insulin [M+H]+ ion using melittin as an internal calibrant.
Recognition of quaternary ammonium compounds using mass spectrometry
Authors: Fisher Dixie L. , Arthur Moseley M. , Mullis James O. , Norwood Daniel L. , Baillie Thomas A.
Published: May 2005

Liquid secondary‐ion mass spectrometry (LSIMS) experiments were performed on a series of model quaternary ammonium chlorides [MCl−] in order to develop a strategy, via an understanding of cluster‐ion formation, for recognition of quarternary ammonium structures. Model structures contained a single quaternary site and various other structural features (for example, conjugated quaternary systems and carboxylic acid groups), using amine hydrochlorides as controls. Cluster ions were examined with both positive‐ and negative‐ion LSIMS, using a range of matrix modifiers. Precursor scans, or ‘molecular weight confirmation scans’, of M (the charged molecular ion of quaternary ammonium compounds) and [M+H]+ ions were used to assist in the observation of cluster ions and to unambiguously demonstrate precursor/product relationships. Positive‐ion experiments typically showed dimeric clusters of [2MQ+ A]+ (A=anion) and [2MQ−H]+ ions, while negative ion experiments produced [MQ + 2A]− ions. Observation of these cluster ions coupled with the lack of an [M−H]− ion are a distinguishing feature of quaternary amines. Additional cluster ions were targeted for distinguishing between protonated amines and quaternary amonium compounds containing a carboxylic acid group. A strategy for recognizing and distinguishing quaternary ammonium structures using LSIMS is proposed, and some initial experiments with thermospray and electrospray are discussed.
Analysis of pyridinoline and its derivatives by scanning‐array four‐sector tandem mass spectrometry
Authors: Self Ron , Stead David A. , Robins Simon P. , Derrick Peter J. , Chen Su
Published: May 2005

Structures of the trifunctional crosslink molecules, pyridinoline, deoxypyridinoline and glucosylgalactosyl‐pyridinoline, have been characterized by positive‐ion liquid secondary‐ion mass spectrometry (LSIMS) and collision‐induced dissociation with scanning‐array four‐sector tandem mass spectrometry. It has been found that: (i) the naturally occurring cations (Cat+) are readily desorbed by positive‐ion LSIMS utilizing glycerol + thioglycerol (1:1) as liquid matrix and dominate the spectra, facilitating accurate mass measurement; (ii) changing the matrix to 3‐nitrobenzyl alcohol leaves little evidence of the cation, and (iii) collision‐induced dissociation of the cations (Cat+) of pyridinoline, deoxypyridinoline and glucosylgalatosyl‐pyridinoline gives a wealth of fragmentation for structure elucidation. These fundamental studies of tandem mass spectra of the known trifunctional crosslink molecules provided valuable structure‐related information, which help in the identification of the tissue‐specific peptides containing these crosslinks. Artefact ions in these tandem mass spectra are remarkably abundant.
A novel hydrogen rearrangement of bifunctional o‐xylylene derivatives in chemical ionization mass spectrometry
Authors: Nakata Hisao , Osogoshi Keisuke , Noda Yasuyo , Abe Ayako , Suzuki Hiroshi
Published: May 2005

A novel hydrogen rearrangement reaction was found in benzyl ions that have a (benzyl) group (Z=O or N) at their ortho position. From deuterium labeling experiments, mass analyzed ion kinetic energy spectra with collisional activation, and examination of structure‐peak intensity correlation, a mechanism is proposed which involves a direct transfer of hydrogen (hydride) to the structurally remote but spatially close cationic center. The possibility of an alternative, less likely mechanism including an ion/neutral complex and/or a proton‐bridged complex has also been discussed.
Total yield measurements in matrix‐assisted laser desorption using a quartz crystal microbalance
Authors: Quist Arjan P. , Huth‐Fehre T. , Sundqvist Bo U. R. , Vertes Akos
Published: May 2005

A quartz crystal microbalance (QCM) is employed to determine the desorption yield of neutral particles in matrix‐assisted laser desorption ionization. For ferulic acid, the matrix substance used, the QCM mass resolution of 1 ng corresponds to a detection limit of ≈︁1012 particles. Sample exposure effects are studied at different fluences by measuring the total desorption yield after consecutive laser pulses fired on the same spot on the sample. The dependence of the total yield on the fluence is studied for different angles of incidence of the laser beam. Varying the distance between the QCM and the sample yields information about the angular spread of the desorbed neutral particles. Additional information about the fluence threshold for the production of charged particles is gained by direct electronic measurements of sample charging.
Electron impact mass spectrometry of some 5‐amino salicylic acid derivatives
Authors: Rizzi Emanuele , Ferrario Francesco , Sala Alberto , Catinella Silvia , Traldi Pietro
Published: May 2005

The electron impact‐induced fragmentation processes of eleven differently substituted 5‐amino salicylic acids were studied by means of mass‐analyzed ion kinetic energy (MIKE) spectroscopy, parent‐ion spectroscopy and accurate mass measurements. Most of the fragmentation processes are related to the cleavages of the 5‐amino substituents. Unusual behaviour is that related to the CO2 loss from the molecular ion, quite significant in the normal electron ionization spectra and completely undetectable in the MIKE spectra.
Cathodic bombardment and sputtering in the 0.5–4.0 torr pressure region of a glow‐discharge ion source
Authors: Mason Rod S. , Milton Dafydd M. P. , Pichilingi Melanie , Anderson Peter D. J. , Tereza Fernandez M.
Published: May 2005

Cathodic ion sputtering energies have been studied in a glow‐discharge ion source, operated in the ranges 0.5–2.0 Torr pressure and 100–1000 V discharge voltage using ion kinetic energy spectroscopy. Average energies in the range 10–20 eV were measured. These energies are very low compared with the theoretical prediction of the charge‐transfer model. In view of this, the high sputtering yields measured are surprising. It is inferred that the sputtering is caused, not by the discharge gas ions as is still widely believed, but by fast discharge‐gas atoms. A means of estimating the average energy of the neutral flux is found by comparing presently measured thresholds with Literature values directly obtained. The average energy seems to be about three times greater than that of the ions. The neutral flux is crudely estimated by comparison of the apparent nett sputter yields measured here with tabulated primary values and taking into account back‐diffusion. It is found to be > 100 times larger than the ion flux. The flux created by charge transfer alone is therefore not enough to explain the high sputtering yields measured. Higher energy ions detected and composed mainly of ionized cathodic atoms appear to be formed in a region intermediate between the negative glow and the cathode, which again is different from the generally held view.
Characterization of glucuronic acid conjugates of a novel angiotensin receptor antagonist
Authors: Bowers Gary D. , Eddershaw Peter J. , Hughes Soraya Y. , Manchee Gary R. , Oxford Janet , Games D. E.
Published: May 2005

Nanogram quantities of glucuronic acid conjugates of GR117289 in rat and dog bile have been analysed by semi‐microbore high‐performance liquid chromatography (HPLC)/ionspray mass spectrometry with on‐line UV diode array detection. The determination of drug metabolites in bile has often proved problematical due to the large number of endogenous components in this biological matrix, in particular the bile acids. Semi‐microbore HPLC is useful for concentrating small quantities of material and, in combination with an on‐line diode array detector, for distinguishing between drug related and endogenous components. A novel angiotensin II receptor antagonist, GR117289, had proved difficult to analyse by thermospray mass spectrometry because of its thermal lability. The use of the less thermally dependent technique of ionspray mass spectrometry allowed the characterization of nanogram quantities of glucuronic acid metabolites of GR117289 in bile.
Halocarbenes as diagnostic tools for mass spectral localization of double bonds
Authors: Schuerch Stefan , Howald Markus , Gfeller Hans , Schlunegger Urs Peter
Published: May 2005

Different halocyclopropanes prepared by cycloaddition of halocarbenes to olefins by phase‐transfer reactions have been analyzed by gas chromatography/mass spectrometry (GC/MS). Starting from CCl2‐adducts, the investigations have been extended to bromine‐ and fluorine‐containing cyclopropanes. As reaction partners, a group of olefins, containing different alkyl substituents, have been selected. Thereby, special attention has been paid to smooth reaction conditions, high reaction yield and simple handling. The suitability for mass spectral analysis is discussed. Fragmentation pathways and diagnostic potential are evaluated. Best results have been obtained by addition of bromofluorocarbene to double bonds. The resulting bromofluorocyclopropanes are considered to be the most promising derivatives for mass spectral localization of double bonds.
Formation of deprotonated molecules [M—H]− of α‐tocopherol under fast‐atom bombardment conditions
Authors: Takayama Mitsuo
Published: May 2005

The formation of deprotonated molecules, [M—H]−, of α‐tocopherol under fast‐atom bombardment (FAB) conditions has been discussed on the basis of a proton subtraction reaction between analyte and matrix molecules. The use of proton‐accepting matrices such as diethanolamine (DEA) and pentamethyleneglycol (PMG) gave higher intensities of the [M—H]− ion and more definitive spectral data than when other matrices, a 1:2 (v/v) mixture of thioglycerol (TG) and dithiothreitol (DTT), or m‐nitrobenzylalcohol (m‐NBA), were used. The order of proton acceptability evaluated for the matrices used was DEA>PMG>DTT>m‐NBA. It was concluded that the proton acceptability, which is measured by gas‐phase basicity or proton affinity, is a most important factor for the formation of both [M + H]+ and [M—H]− ions under FAB conditions. Further, the formation of molecular ions, M+·, under FAB conditions and the formation of [M—H]− ions by electron impact have been discussed by using α‐tocopherol.
Simple and sensitive quantitation method for mevalonic acid in plasma using gas chromatography/mass spectrometry
Authors: Ishihama Yasushi , Mano Nariyasu , Oda Yoshiya , Hiyoshi Hironobu , Ikuta Hironori , Yoshida Yutaka
Published: May 2005

The combination of gas chromatography and mass spectrometry using a polar capillary column and isobutane chemical ionization made it possible to determine mevalonic acid (MVA) as the lactone at subnanogram levels using 1 mL of plasma. The pretreatment procedure consisted of only three steps, namely lactonization, washing with chloroform and liquid/liquid extraction. This simple, rapid and sensitive method, having good precision and accuracy, is useful for evaluating the change of plasma MVA, which is well correlated with whole‐body cholesterol biosynthesis.
Mass shifts due to ion/ion interactions in a quadrupole ion‐trap mass spectrometer
Authors: Cleven Curtis D. , Cox Kathleen A. , Graham Cooks R. , Bier M. E.
Published: May 2005

Mass spectra recorded using a Paul ion trap, operated in the mass‐selective instability scan mode, give peak positions which are shown to depend on ion abundance. The isolated molecular ions of benzene, anisole, cresol, and n‐butylbenzene are ejected during the mass selective instability scan at times which display a linear dependence on ion abundance for low populations of trapped ions. Remarkably, the degree to which the peaks are shifted is also compound dependent. Mass shifts are also influenced by the presence of other ions in the trap and this effect is amplified as the mass difference between the analyte and matrix ions decreases. Mass shifts are also affected by the helium pressure which controls the ion density. Extrapolation to zero ion abundance and to zero helium pressure is suggested as a method of eliminating these effects and hence of improving the mass measurement accuracy attainable using the ion trap.
Mass‐selective analysis of ions in time‐of‐flight mass spectrometry using an ion‐trap storage device
Authors: Fountain Scott. T. , Lee Heewon , Lubman David M. , Chen Chung‐Hsuan
Published: May 2005

A quadrupole ion trap was used as a front‐end device for selecting specific ions formed via matrix‐assisted laser desorption for analysis in time‐of‐flight mass spectrometry. Using low‐voltage auxiliary RF signals, the ion trap can be used to resonantly eject all but a selected mass‐to‐charge range prior to time‐of‐flight mass analysis. A series of simple analog resonance ejection circuits were developed to provide this selective ion trapping. These circuits use both single‐ and modulated‐frequency waveforms applied directly to the repeller endcap of the quadrupole ion‐trap source in a monopolar fashion. Commercially available waveform generators, as well as a multichannel voltage‐controlled oseillator circuit, were used for resonant ion ejection and ion isolation prior to pulsed extraction into the time‐of‐flight mass spectrometer. The analytical utility of these circuits was tested on a series of biologically active peptides from m/z 700 to 1650 using matrix‐assisted laser desorption/ionization (MALDI) directly into the ion trap. These simple analog circuits were found to provide a number of useful qualitative improvements in the ion‐trap/reflectron time‐of‐flight device including the broadband removal of matrix background ions formed via MAI DI and the isolation of molecular ions from complex peptide mixtures. The utility of this methodology for tandem mass spectrometry, including collision‐induced dissociation and photodissociation, is discussed.
Maximum entropy deconvolution of heterogeneity in protein modification: Protein adducts of 4‐hydroxy‐2‐nonenal
Authors: Bruenner Bernd A. , Daniel Jones A. , Bruce German J.
Published: May 2005

To explore the chemistry of the reactions of the cytotoxic aldehyde trans‐4‐hydroxy‐2‐nonenal (HNE) with proteins, we incubated this aldehyde in vitro with β‐lactoglobulin B, a model protein of molecular weight 18 277 Da. Direct characterization of reaction products using electrospray ionization mass spectrometry yielded spectra whose complexity suggested extensive product heterogeneity. Spectra were transformed to a true mass scale using both a conventional transform algorithm and a maximum entropy algorithm. Both transformations demonstrated the formation of aldehyde‐protein adducts containing from three to nine aldehyde molecules per molecule of protein. Maximum entropy deconvolution resolved Schiff base adducts and/or dehydration products, differing from the Michael addition adducts by 18 Da. The dominant reaction pathway, however, was Michael addition of the aldehyde to nucleophilic functional groups on the protein. The large number of Michael adducts relative to the one available cysteine requires that other amino acids, such as histidine and lysine, also be modified. The data suggest that methods for analysis of HNE that involve displacement of Schiff base groups from proteins will only recover a small fraction of HNE.
An automated liquid chromatography/mass spectrometry system coupled on‐line with microdialysis for the in vivo analysis of contrast agents
Authors: Michelsen Peter , Pettersson Göran , Games D. E.
Published: May 2005

An automated high‐performance liquid chromatography (HPLC)/mass spectrometry instrument coupled on‐line with a microdialysis probe is described for the analysis of contrast agents in biological fluids. This system is used for pharmacokinetic and structure elucidation studies of contrast agents used in X‐ray and magnetic resonance imaging investigations. Additionally an LC/MS system for the direct analysis of urine, that obviates the need for conventional sample clean‐up, is described.
Revealing the mammalian lignan precursor secoisolariciresinol diglucoside in flax seed by ionspray mass spectrometry
Authors: Bambagiotti‐Alberti Massimo , Coran Silvia A. , Ghiara Caterina , Giannellini Valerio , Raffaelli Andrea , Traldi P.
Published: May 2005

Ionspray mass spectrometry allowed the rapid detection and unambiguous identification of secoisolariciresinol diglucoside, an important mammalian lignan precursor occurring in flax seed. It was observed that this compound is embedded in a complex form, probably a complex glucoside of still undisclosed structure, among the polar solvent extractables of flax seed from which it could not be released as such without the intervention of alkaline methanolysis. Comparison of ionspray mass spectra of untreated and methanolysed flax‐seed extracts confirmed methanolysis as the crucial step in setting up any further analytical or preparative procedure concerned with secoisolariciresinol diglucoside.
An automated, open‐access service to synthetic chemists: Thermospray mass spectrometry
Authors: Brown David V. , Dalton Melanie , Pullen Frank S. , Perkins George L. , Richards Don , Cottee Frank H.
Published: May 2005

Nuclear magnetic resonance (NMR) and mass spectrometry (MS) are the major spectroscopic tools used by synthetic organic chemists to monitor the steps of their syntheses. Rapid confirmation of the structure at each synthetic step is vital for efficient progress to the desired product. In many laboratories automated open‐access NMR is routine. This often leaves mass spectrometry as a rate‐limiting step in structure confirmation. The key information the chemist needs from a mass spectrum is the relative molecular mass (RMM). We have therefore developed an automated, open‐access thermospray mass spectrometry service, in which a chemist logs a sample into a queue on the mass spectrometer, and a short time later takes the mass spectrum away. The whole process occurs without any intervention by a mass spectrometrist. This has made mass spectra available as rapidly as NMR spectra, so that chemists can obtain the data they need to confirm synthetic structures within less than two hours.
Comparison of peptide analysis results for horse, bovine and dog cytochrome c using capillary electrophoresis/mass spectrometry with untreated capillary column and basic buffer condition
Authors: Takada Yasuaki , Nakayama Kanae , Yoshida Motoko , Sakairi Minoru
Published: May 2005

Peptide analysis of cytochrome c using capillary electrophoresis/mass spectrometry was demonstrated to be a rapid, sensitive and useful technique for providing information concerning the location of variation. We analyzed tryptic digests of horse, bovine and dog cytochrome c, and compared the peptide analysis results for information concerning amino acid sequences in proteins. The differences in amino acid sequence were confirmed by taking into consideration that all the other fragments are identical in each map. The use of an untreated capillary column with basic buffer condition (water+acetonitrile+(20 g/L) ammonium carbonate (70/20/10), pH 9.2) had a reproducibility of migration times to within about 2%.
Resolution and spectral‐line shapes in the reflecting time‐of‐flight mass spectrometer with orthogonally injected ions
Authors: Laiko V. V. , Dodonov A. F. , Cotter R. J.
Published: May 2005

Principal factors limiting the resolution of time‐of‐flight (TOF) mass spectrometers based on ‘orthogonal’ ion beam acceleration have been studied theoretically. It has been found that the construction of the orthogonal acceleration TOF mass analyzer enables, in some cases, the simultaneous compensation of both ion spatial and initial velocity distributions by appropriate selection of ion‐mirror potentials. This analytical result has been proved by numerical simulation of spectral line shapes. The influence of elementary cell dimensions of grids on the mass resolution has been investigated by the numerical integration of a large number of ion trajectories. The grids consisting of a set of parallel and equally spaced wires have been treated. Analytical approximations of the electrical field potential of the grids have been used. It has been found that optimization of TOF mass analyzers should include the treatment of ion scattering by grids.
Investigation of protein‐protein noncovalent interactions in soybean agglutinin by electrospray ionization time‐of‐flight mass spectrometry
Authors: Tang Xue‐Jun , Fred Brewer C. , Saha Sanat , Chernushevich Igor , Ens Werner , Standing Kenneth G. , Chait Brian T.
Published: May 2005

Noncovalent interactions in soybean agglutinin (SBA) were studied on an electrospray ionization (ESI) time‐of‐flight mass spectrometer constructed recently at the University of Manitoba. The high m/z range and high sensitivity of the instrument together with mild ESI interface conditions turned out to be ideal for detecting this noncovalently bonded tetrameric protein (MW ∼ 116 000 Da) in low charge states (z=23 to 27). By altering the acetonitrile content of the SBA solutions it was shown that the observed SBA tetramers are due to structurally specific noncovalent associations in solution. Octamers and dodecamers (MW ∼ 350 000 Da) were also detected. Information on the quaternary structure of the tetramers was obtained by analyzing the fragment‐ion spectrum resulting from the collision‐induced dissociation of the tetramer ions.
Determination of molecular structures of photolysis products of substituted aromatic azides in diethylamine solvent by gas chromatography/mass spectrometry
Authors: Senthil Vellala , Soundararajan N.
Published: May 2005

We have photolyzed methyl‐3‐azido‐4‐fluoro benzoate, methyl‐3‐azido‐6‐fluoro benzoate, and methyl‐3‐azido‐4,6‐difluoro benzoate, in neat diethylamine and the resultant products were analyzed by capillary column gas chromatography/mass spectrometry. Two types of products were formed. The first type of product includes substituted anilines and adducts of an aryl nitrene with one molecule of diethylamine. The second type of product includes adducts derived by addition of two molecules of diethylamine to ketenimines with elimination of hydrogen fluoride and also products derived from these with subsequent elimination of hydrogen cyanide molecule. These hydrogen cyanide eliminated products appear to have been formed by secondary photolysis of the initially formed adducts.
High performance liquid chromatography/ionspray mass spectrometry of N‐ethylmaleimide and acrylic acid ester derivatives for bioanalysis of thiol compounds
Authors: Jemal Mohammed , Hawthorne Dara
Published: May 2005

High performance liquid chromatoraphy/ionspray mass spectra of N‐ethylmaleimide (NEM) and acrylate derivatives of the sulfhydryl compound BMS186716 exhibited a variety of fragmentation patterns, in positive‐ or negative‐ion mode, providing a wide choice of conditions for developing a bioanalytical method based on selected‐ion monitoring. Because the NEM derivative gave two chromatographic peaks (due to two diastereomers) whereas the acrylate derivative gave a single peak, the acrylate derivatization was chosen for further investigations. While BMS186716 in blood or plasma was extremely unstable, the compound could be stabilized by adding methyl acrylate (MA) to the biological matrix, owing to instantaneous reaction to form the stable BMS186716‐MA derivative. This stabilization scheme is being investigated for developing a sensitive bioanalytical liquid chromatographic/mass spectrometric method for BMS186716.
Fragmentation reactions of the trimethylsilyl adducts of C6 ketones
Authors: Bosma Nancy L. , Harrison Alex G. , Munson B.
Published: May 2005

The unimolecular (metastable ion) and collision‐induced fragmentation reactions of the trimethylsilyl cation adducts of six C6 ketones have been studied by tandem mass spectrometry. A major unimolecular fragmentation channel involves regeneration of the trimethylsilyl cation; other fragmentation channels involve elimination of (CH3)3SiOH, C5H10, C4H8 and C3H6 from the adduct ions. Some mechanistic detail has been obtained from a study of the adducts with deuterium‐containing ketones, and the reactions observed are compared with the fragmentation reactions of the protonated ketones. Collision‐induced dissociation (CID) of the adduct ion results in predominant formation of (CH3)3Si+. However, in the high energy (6 keV) CID new minor reaction channels, involving elimination of alkanes, CH4 to C4H10, become accessible. It is concluded that tandem mass spectrometry of the trimethylsilyl adducts provides only limited ability to distinguish between isomeric ketones.
Gas‐phase reactions of transition metal carbonyl anions and atomic metal anions with nitrous oxide and dioxygen: Oxygen atom transfer and ligand exchange in reactions with nitrous oxide
Authors: van den Berg Klaas Jan , Ingemann Steen , Nibbering Nico M. M. , Gregor Ian K.
Published: May 2005

The gas‐phase reactions of a series of metal carbonyl anions M(CO) (M=Cr, n=2–5; M=Mn, n=1–5; M=Fe, n=1–4) with nitrous oxide and dioxygen have been studied by use of Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry. With nitrous oxide, most of the metal carbonyl ions react by oxygen atom transfer leading to oxo‐metal anions and oxo‐metal carbonyl anions. The Cr− and Fe− ions also react relatively easily with nitrous oxide by oxygen atom abstraction to form CrO− and FeO−, respectively. Experiments with N15NO reveal that loss of a CO molecule from a collision complex is a significant ligand exchange channel for the Mn(CO), Mn(CO) and Fe(CO) ions. The nitrous oxide molecule remains intact in the resultant product ions, M(CO)n(N2O)− with M=Mn, n=2 and 3; and M=Fe, n=2. The losses of 15NN and 15NN + CO in the collision‐induced dissociations of the Mn(CO)3(N15NO)− ions, in combination with the relatively facile occurrence of oxygen atom transfer, are taken to mean that coordination of the metal centre to the oxygen atom is preferred over bond formation to the terminal nitrogen atom of the nitrous oxide molecule. The metal carbonyl anions react readily with dioxygen to form mainly oxo‐metal ions as well as oxo‐ and dioxo‐metal carbonyl anions in relative yields which depend on the nature of the metal and the number of CO ligands in the reactant ion.
Investigation of mammalian lignan precursors in flax seed: First evidence of secoisolariciresinol diglucoside in two isomeric forms by liquid chromatography/mass spectrometry
Authors: Bambagiotti‐Alberti Massimo , Coron Silvia A. , Ghiara Caterina , Moneti Gloriano , Raffaelli Andrea , Traldi P.
Published: May 2005

A strong research effort has been devoted in recent years to the mammalian lignans enterolactone and enterodiol because of their claimed protective effects against breast and colon cancer. Some plant lignans appear to be precursors of these molecules. This paper reports a novel identification procedure for one of these precursors, the secoisolariciresinol diglucoside, in the extracts of defatted flax‐seed meal. The procedure is based on high‐performance liquid chromatography coupled with either ionspray or continuous‐flow fast‐atom bombardment mass spectrometry. The application of these techniques allowed the identification in flax seed of two isomeric forms of this precursor for the first time. The isomers are reasonably the two diastereoisomers, due to the two equivalent stereogenic centers present in the molecule.