bluuebunny/crossref_metadata_2025 huggingface dataset:
Radical identification by liquid chromatography/thermospray mass spectrometry
Authors: Iwahashi Hideo , Parker Carol E. , Mason Ronald P. , Tomer Kenneth B.
Published: May 2005

Radical adducts of 5,5‐dimethyl‐1‐pyrroline N‐oxide (DMPO) with hydroxyl, methanol‐derived, and ethanol‐derived radicals were detected by a combination of liquid chromatography with either electron paramagnetic resonance or thermospray mass spectrometry (LC/EPR or LC/TSP‐MS) in the Fenton system (with methanol or ethanol). One radical adduct was observed in the reaction of DMPO with the hydroxyl radical or the methanol‐derived radical, while two adducts were detected in the reaction of DMPO with ethanol‐derived radicals. The LC/TSP‐MS spectra showed quasi‐molecular ions [M+H]+ at m/z 146 and m/z 160 for the methanol‐derived and ethanol‐derived radical adducts, respectively, and an apparent molecular ion M+ at m/z 130 for the hydroxyl radical adduct. Use of methyl‐D3 alcohol (CD3OH) and ethyl‐D5 alcohol (CD3CD2OH) indicated that carbon‐centered radicals are formed. Experiments with partially deuterated ethanol (CD3CH2OH and CH3CD2OH) indicated that the two adducts observed in the reaction of DMPO with ethanol‐derived radicals correspond to the two diastereomeric adducts of DMPO with the α‐hydroxyethyl free radical.
An experimental determination of the energy of the first triplet doubly‐ionized state of ammonia
Authors: Griffiths W. J. , Harris F. M.
Published: May 2005

The double‐ionization energy of NH3 to the first triplet state of the dication has been measured by double‐charge‐transfer spectroscopy using OH+ as the projectile ion. The value determined, 37.9±0.5 eV, is in excellent agreement with that calculated by Tarantelli et al. [Chem. Phys. Lett. 117, 577 (1985)] using the configuration interaction method.
Ion optical considerations in tandem mass spectrometry
Authors: Boerboom A. J. H.
Published: May 2005

A review of tandem sector‐field mass spectrometers is given with features of various combinations of electric and magnetic sector fields and quadrupole lenses and, eventually, a Wien filter. In particular, a tandem mass spectrometer is described, constructed at Amsterdam, with post‐acceleration, variable dispersion and array detection. The simultaneously‐detected mass range varies from 1:1.06 through 1:12, the resolution in the second stage amounts to 1000 (single‐focusing), the dynamic range is 5000:1, and the sensitivity is such that less than 1 fmol of sample can be detected and identified.
A new gas chromatography/tandem mass spectrometry method for analysis of monoaromatic steroids in petroleum
Authors: Nali M. , Corana F. , Riva A. , Albrecht P. , Wehrung P.
Published: May 2005

A new gas chromatography/tandem mass spectrometry (GC/MS/MS) analytical approach for monoaromatic steroids is described in comparison with a more conventional GC/MS analysis. Some examples are reported both on standards and on real samples.
Collision‐activated dissociation studies of alkylamines formed from copper‐induced dealkylation of N‐alkylporphyrins
Authors: Naylor Stephen , Gibbs Anthony H. , Lamb John H. , De Matteis Francesco
Published: May 2005

A low‐energy (5–450 eV) collision‐activated dissociation (CAD) study of a series of aliphatic amines revealed that at collision energies above 200 eV, charge‐site‐initiated fragmentation occurs. The resulting fragment ions can be utilized in the characterization of alkyl substituents of di‐ and trisubstituted aliphatic amines. In the presence of Cu2+ and a suitable nucleophile, such as n‐dodecylamine, N‐alkyl protoporphyrins dealkylate to afford copper protoporphyrin and an alkyl‐dodecylamine adduct. A CAD study of a number of alkyl‐dodecylamine adducts derived from the copper‐induced dealkylation of synthetic N‐alkyl protoporphyrins, using charge‐site‐initiated fragment ions, showed that the alkyl group was trapped by the nucleophilic amine present. Subsequently this method was used to identify the alkyl group of a biologically derived N‐alkyl protoporphyrin.
Alternative driving functions for a collision quadrupole
Authors: Barber M. , Gordon D. B. , Woods M. D.
Published: May 2005

The work presented here introduces a new variable parameter in the design of quadrupole collision cells. A brief summary of the mathematical theory is given to demonstrate how the maximum value of the parameter q may be altered. This is achieved through changing the driving function used for the rod potentials.
The use of tandem mass spectrometry as a problem‐solving tool in the industrial environment
Authors: Rollins K. , Scrivens J. H. , Jennings R. C. K. , Morden W. E. , Welby J. K. , Bateman R. H.
Published: May 2005

This paper deals with a number of the benefits associated with a variety of tandem mass spectrometer geometries and the way in which these configurations have been applied to the solution of real problems. It discusses the use made of a variety of tandem mass spectrometry approaches to the study of analytical problems of industrial relevance. ICIs utilization of tandem mass spectrometry has grown substantially from an initial involvement in the early 1980s to a point where a number of instruments have been installed and used predominantly for trace analysis, structural studies and in the characterization of complex mixtures. We have selected a small number of examples of the use of the various tandem mass spectrometry approaches emphasizing the unique features of the technique.
Use of triethylammonium formate to enhance sensitivity in negative‐ion liquid chromatography/thermospray‐mass spectrometry
Authors: Steffenrud S. , Dewey Elisabeth , Maylin G.
Published: May 2005

The major objective of this investigation was to find a thermospray buffer that would decrease ion/molecule reactions in the gas phase. This would cause solution chemistry and ion evaporation to be major parameters controlling ion production. Using triethylammonium formate, protonation by ion/molecule reaction in the gas phase was decreased as indicated by the effect of solution pH on ion production. The detection limits in the full‐scan mode for some amphoteric compounds and acids were one magnitude lower than those obtained with ammonium acetate or ammonium formate buffers. A few examples of sensitive full‐scan detection demonstrate the usefulness of this novel buffer for negative‐ion thermospray liquid chromatography/mass spectrometry.
Characterization of cyclodextrins using ion‐evaporation atmospheric‐pressure ionization tandem mass spectrometry
Authors: Huang Eric C. , Henion Jack D.
Published: May 2005

A tandem mass spectrometer equipped with the pneumatically‐assisted electrospray (ion spray) liquid chromatography/mass spectrometry interface and an atmospheric‐pressure ionization source was used for characterization of underivatized cyclic oligosaccharides. Protonated singly charged molecular ions were generated via ion‐evaporation mechanism(s). The formation of doubly charged molecular ions from the model compounds appears to be related to the channel diameter of these cyclic oligosaccharides. Tandem mass spectrometry (MS/MS) was used to study collision‐induced dissociation of the protonated molecule and showed exclusive cleavage of the glycosidic bond. The molecular weights of these oligosaccharides as well as the number of sugar units were confirmed by MS/MS. The potential application of MS/MS for target compound analysis was demonstrated by the parent‐ion scan method with a synthetic mixture.
Magic numbers in kinetic energy releases for unimolecular decompositions of proton‐bound acetone and acetone/water clusters
Authors: Lifshitz C. , Iraqi M. , Peres T.
Published: May 2005

Magic numbers were observed for kinetic energy releases (KERs) upon desolvation of proton‐bound neat acetone clusters and mixed acetone/water clusters. The results for the neat clusters are successfully reproduced by the evaporative ensemble model of Klots. We conclude that the phenomenon is general, namely that the KER for a series of clusters goes through a maximum for the cluster of size n having special stability.
On the formation of doubly charged fragment and cluster ions of oxygen‐ and sulfur‐containing substances in field ionization and field desorption mass spectrometry
Authors: Kosevich M. V. , Shelkovsky V. S.
Published: May 2005

The appearance of doubly charged molecular, fragment and cluster ions in the field desorption and field ionization mass spectra of thiotepa are discussed. A comparison with the field‐desorption mass spectra of some other oxygen‐ and sulfur‐containing compounds is made and the conclusion reached, that the formation of doubly charged fragment [MO]2+, [MS]2+, and cluster [(MO)M]2+, [(MS)M]2+ ions is a characteristic behaviour of several types of substances containing O and S groups under the conditions of high electric field.
Gas chromatography/mass spectrometry in the elucidation of the structure of piperidine alkaloids
Authors: Maksimović Mirjana , Šober Miroslav , Nikolin Branko
Published: May 2005

Piperidine heterocycles are present in the structure of many alkaloids, for example coniine in the structures of lobelia, cocaine alkaloids and sedum alkaloids, Sedum alkaloids are 2,6‐disubstituted derivatives of piperidine or N‐methylpiperidine. Extracts obtained from Sedum acre L. were investigated for the presence of alkaloids by gas chromatography/mass spectrometry. Identification has been carried out on the basis of retention time, molecular ion mass and characteristic fragmentation. Investigated extracts contained unknown alkaloids which belong to the piperidine group of sedum alkaloids. Mass spectral fragmentation patterns and a proposed structure for the unknown alkaloids are discussed.
Electrospray interface for liquid chromatography/mass spectrometry
Authors: Hiraoka Kenzo , Kudaka Ichiro
Published: May 2005

The positive and negative ions produced by electrospray atomization from solutions of various molecules were detected using a high‐pressure quadrupole mass spectrometer. The electrospray interface for liquid chromatography/mass spectrometry was investigated in various respects, i.e., the effect of needle voltage on the total current, solvent dependence, the effect of surrounding gas, gas temperature, and the sensitivity of detection of mass‐analysed ions. In the positive‐ion mode, the detection limits of ionic samples in solution are found to be lower than the order of parts per billion. The addition of CCl4 in solution inhibits a breakdown to discharge at the needle tip and makes it possible to electrospray at much higher needle voltages. It was found that neutral samples in solutions with concentrations of ≥ 10−4 M could easily be detected by producing a small corona discharge on the tip of the liquid cone (atmospheric pressure ionization).
Sequence‐specific fragmentation from oligopeptides using plasma‐desorption mass spectrometry
Authors: Buko Alexander M. , Sarin Virender K.
Published: May 2005

252Cf plasma‐desorption mass spectrometry (PDMS) has been demonstrated to provide sequence‐specific fragmentation for several oligopeptides. The nature of the fragment ions observed is generally similar to that observed using liquid secondary‐ion mass spectrometry (LSIMS) and can be observed using less sample than LSIMS requires, but PDMS spectra are acquired at a lower resolution. In addition, the molecular weight of some of the oligopeptides studied exceeds that which is generally accepted as within the sequence range of LSIMS. The specific series of sequence ions that predominate in the PDMS spectra appear to be related to the amino acid compositions and sequences of the oligopeptides.
Identification of prenylated flavonoids using fast‐atom bombardment mass spectrometry
Authors: Takanyama Mitsuo , Fukai Toshio , Ichikawa Koichi , Nomura Taro
Published: May 2005

6‐ and 8‐prenylated flavanones were distinguishable from each other by means of their fast‐atom bombardment (FAB) spectral patterns, while the corresponding electron ionization spectral patterns were very similar to each other. It was suggested that 6‐ and 8‐prenylated flavonoids can, in general, be distinguished by means of FAB.
252Cf‐plasma desorption and cesium‐ion liquid secondary‐ion mass spectrometric analysis of recombinant proteins
Authors: Tsarbopoulos A. , Pramanik B. N. , Reichert P. , Siegel M. M. , Nagabhushan T. L. , Trota P. P. , Jardine I.
Published: May 2005

The keV Cs+ liquid secondary‐ion mass spectrometry (LSIMS) and 252Cf‐plasma desorption (PD) mass spectra of recombinant proteins in the 10–25 kDa mass range are compared. Both techniques showed comparable mass accuracy and sensitivity, and in the case of LSIMS, remarkably short analysis time. Analysis by the PD/nitrocellulose method demonstrated slightly higher sensitivity and relativity lower dependence on the salt and buffer content of the protein sample.
Solvent‐induced conformational changes of polypeptides probed by electrospray‐ionization mass spectrometry
Authors: Loo Joseph A. , Loo Rachel R. Ogorzalek , Udseth Harold R. , Edmonds Charles G. , Smith Richard D.
Published: May 2005

Electrospray‐ionization (ESI) mss spectrometry is used to monitor higher order structural changes of polypeptide induced by alteration of the pH or organic solvent composition in the protein solution environment. A bimodal charge‐state disribution is observed in the ESI mass spectrometry of ubiquitin (relative molecualr mass 8565) in solution containing small amounts (<20%) of organic solvents. The distribution of peaks at high m/z (low‐charge state) is found to represent the protein in its native, globular state; the higher‐charge‐state distribution is characteristic for a more extended conformation. Addition of methanol denaturant in excess of 40% v/v is needed to eliminate the low‐charge‐state distribution completely. Lesser amounts of acetonitrile, acetone, or isopropanol (∼20%) are reqiored to denature the ubiquitin protein. Other proteins showing conformational efects in their ESI mass spectra are also illustrated. While the ESI spectra are related to solution phase structure, ESI‐tandem mass spectrometry of multiply charged molecular ions of different conformation is suggested as a probe of gas‐phase protein three‐dimensional structure.
Various techniques for the mass spectrometric analysis of valatile traces in environmental matrices using a direct‐coupled, paked column
Authors: Hille Jürgen
Published: May 2005

Volatile trace impurities from enviornmental matrices were enriched on a packed column directly coupled to the vacuum system of a mass spectrometer. Traces in gaseous samples (air) were enriched without sample preparation. Traces from liquid samples (water) were separated on‐line by isothermal vacuum distillation, and from solid samples (soil) by vacuum desorption before adsorptive enrichment. Pressure reduction for sample introduction into the high vacuum of the mass spectrometer is realized by decreasing the pressure during enrichment and by cryo‐pumping, in which the packed column is immersed in liquid nitrogen (77 K). Besides the simple thermal desorption of enriched traces into the mass spectrometer, the column can be heated locally for carefully directed desorption of substance zones. Two alternative principles: ‘Frontal Desorption’ and ‘Purging’ are possible. Detection limits of ng/g were achieved for traces of chlorinated and aromatic hydrocarbons in air and water.
Location of unsaturated positions in phosphatidyl cholines by consecutive‐reaction monitoring
Authors: Bryant Duncan K. , Orlando Ron , Boyd R. K.
Published: May 2005

Consecutive‐reaction monitoring (MS3) of negative ions has been shown to be useful in locating double bonds in the fatty acid ester groups of individual phosphatidyl cholines present in complex mixtures. This information is derived from charge‐remote fragmentations of carboxylate anions produced by collisional activation of the [MCH3]− precursor ions from phosphatidyl cholines. The added selectivety of this technique increases the sensitivity, relative to that of tandem mass spectrometry (MS2), such that only 3 pmol are needed to perform this analysis.
Analysis of polycyclic aromatic compounds by supercritical fluid charomatography/mass spectrometry using atmospheric‐pressure chemical ionization
Authors: Anacleto J. F. , Ramaley L. , Boyd R. K. , Pleasance S. , Quilliam M. A. , Sim P. G. , Benoit F. M.
Published: May 2005

The development of microbore packet‐column supercritical fluid chromatography/atmospheric pressure chemical ionization mass spectrometry (SFC/APCI‐MS) for the analysis of polycyclic aromatic compounds (PAC) is described. The SFC system was coupled to the mass spectrometer using an improved interface designed to accommodate commercially available fused silica restrictors. The atmospheric pressure chemical ionization characteristics of PAC are discussed and the use of chemical ionization reagents to modify the type of spectra obtained is described. With selected‐ion monitoring techniques the interface provided detection limits in the low picogram range for individual PAC standards. Using a photoionization detector for the off‐line optimization of chromatographic conditions, SFC/APCI‐MS was applied to the analysis of complex mixtures of PAC in coal tar and tar sand oil extracts. Tandem mass spectrometry was used to provide structural information.
Positively and negatively charged water cluster ions generated via liquid chromatography/thermospray mass spectrometry
Authors: Tinke A. P. , Heeremans C. E. M. , van der Hoeven R. A. M. , Niessen W. M. A. , van der Greef J. , Nibbering N. M. M.
Published: May 2005

The formation of singly protonated water clusters in the positive‐ion mode and singly deprotonated water clusters as well as singly negatively charged water clusters in the negative‐ion mode with a thermospray system running on pure water and in the discharge‐on mode is described. The influence of the potential at the repeller electrode opposite to the sampling cone recalls previous mechanistic discussions on the repeller influence. Application of these water cluster ions to tuning and calibration in the thermospray mode is proposed.
Conformational changes in proteins probed by hydrogen‐exchange electrospray‐ionization mass spectrometry
Authors: Katta Viswanatham , Chait Brian T. , Carr Steven
Published: May 2005

Hydrogen‐exchange electrospray‐ionization mass spectrometry is demonstrated to be an effective new method for probing conformational changes of proteins in solutions. The method is based on the mass spectrometric measurement of the extent of hydrogen/deuterium exchange that occurs in different protein conformers over defined periods of time. Results are presented in which hydrogen‐exchange electrospray‐ionization mass spectrometry is used to probe conformational changes in bovine ubiquitin induced by the addition of methanol to aqueous acidic solutions of the protein.
The resonantly enhanced of two‐photon ionization and electron ionization of trypyophan molecules in beams formed by laser evaporation of aqyeous cryogenic matrix
Authors: Elokhin V. A. , Krutchinsky A. N. , Ryabov S. F. , Cooks R. G.
Published: May 2005

The mass spectra resulting from election ionization and resonantly enhanced two‐ionization of amino acid trytophan molecules evaporated by the first harmonic frequency of a Nd‐YAG laser from an aqueous crygenic matrix were obtianed. The resonantly enhanced two‐photon spectra in the region of 0‐0 origin bands of tryptophan conformers was also measured.
Comparison of mass spectra obtained using 252Cf plasma‐desorption and electron‐avalanche‐desorption mass spectrometry
Authors: Zubarev R. A. , Bondrenko P. V. , Knysh A. N. , Rozynov B. V.
Published: May 2005

Direct comparision of two ionization techniques, 252Cf plasma‐desorption and electron‐avalanche‐desorption, is given in various aspect. signification differences were observed in the low‐mass region, and in the spectra of volatile compounds and CsI samples, as well as in the fragmentation pattern of alanilnorleucine. On the other hand, a rather high degree of similarity was obtained in spectra of nitrocellulose and some cyclic depsipeptides, both in typical values of peak width and of the high‐mass background character. The conclusion is made, that electron‐avalanche desorption is a rather complex process involving various factors.
Mass spectral characteristics of okadaic acid and simple derivatives
Authors: Bencsath F. Aladar , Dickey Robert W. , Edmonds C. G.
Published: May 2005

Electron ionization (EI), chemical ionization (CI) and fast‐atom bombardment (FAB) mass spectra of the marine toxin okadaic acid and its syntheticf methyi, pentafurobenzyl, and trimethylislyl ester and ether derivatives were generated. Several ionization conditions and‐processing methods were used to obtain positive‐ and negative‐ion conventional spectra and tandem (MS/MS) spectra. The EF and the positive‐ion CI spectra provided fragment ions characteristic of the structure, and the negative‐ion CI and FAB spectra provided molecular ions. The addition of alkali salts to the FAB matrix resulted in reduced fragmentation and the formation of intense alkali‐metal‐cationized molecules. Pentafluorbenzyle ester derivatives provided intense carboxylate ions under electron‐captute ionization. Analytically useful MS/MS spectra obtained by low‐energy collision‐induced decomposition of the carboxylate anion produced from the tetrasilylated pentafluorobenzylokadaate.
Structural characterization of isomeric didehydro amino acids using chemical ionization
Authors: Hamdan M. , Scaudola M. , Gaviraghi G. , Tarzia G. , Bedini A. L. , Spadoni G. , Curcuruto O. , Traldi P.
Published: May 2005

The positive‐ion mass spectra of a number of didehydro amino acids (DDAA) obtained by electron ionization (EI) and chemical ionization (CI) using different regent gases as well as the collision‐induced dissociation (CID) of mass‐selected odd‐electron ions and/or protonated molecules have been performed on a multiple quadrupole instrument. The positive‐ion EI/CI mass spectra presented display a number of differences which are expected from different isomeric structures. Furthermore, differences associated with the proton affinities of the reagent gases are clearly evident in the poisitive‐ion chemical ionization mass spectra as well as in some CID spectra of protonated molecules. This investigation demonstrates the suitability of chemical ionization for characterization of isomers of this important class of compounds and underlines the effect of the proton affinity of the reagent gas on the overall character of the positive‐ion chemical ionization spectra.
Metastable dissociation of multiphoton‐ionized xenon clusters
Authors: Yamada Yasuhiro , Takayanagi Toshiyuki , Furukawa Katsutoshi , Ohno Shin‐ichi
Published: May 2005

Xenon cluster ions (Xe) were produced by multiphoton ionization at 266 nm of neutral clusters resulting from supersonic expansion of xenon gas. Metastable dissociations Xe→Xe + Xe (where n=2−19) were observed by an angular reflectron time‐of‐flight mass spectrometer. Clusters of some particular sizes were found to be especially unstable, the highest dissociation rate obtained being for Xe. Furthermore, the dissociation rate tended to increase with increase of cluster size (n), in agreement with the evaporative ensemble model which has been developed by Klots.
Facile assignment of sequence ions of a peptide labelled with 18O at the carboxyl terminus
Authors: Takao Toshifumi , Hori Hideaki , Okamoto Kazutake , Harada Akira , Kamachi Mikiharu , Shimonishi Yasutsugu , Matsuo Takckiyo
Published: May 2005

The combination of collision‐induced dissociation (CID) and linked‐scan analysis was used for analysing the sequence ions from the precursor ion of a peptide, which had been labelled with 18O at its carboxyl terminus (C‐terminus) using 40 atom % H218O. The CID and linked‐scan mass spectrum of the labelled peptide gave two series of sequence‐ion signals: the one, originating from the C‐terminus of the labelled peptide, showed a doublet signal due to the part‐incorporation of 18O into the carboxyl group at the C‐terminus, while the other, originating from the amino terminus (N‐terminus), has the natural isotopic ion distribution. From the distribution of the isotopic ions in a single CID spectrum, the sequence ions containing the C‐terminus could be readily differentiated from those containing the N‐terminus, allowing the facile assignment of sequence ions to the amino‐acid sequence of peptide by CID and linked‐scan analysis. This method was successfully applied to determination of the amino‐acid sequence of the light‐chain of mouse anti‐porphyrin monoclonal antibody.
High mass‐resolution using a quadrupole ion‐trap mass spectrometer
Authors: Williams Jon D. , Cox Kathleen A. , Cooks R. Graham , Kaiser Raymond E. , Schwartz Jae C. , Gaskell S. J.
Published: May 2005

Modifications have been made to the quadrupole ion‐trap mass spectrometer (ITMS) to improve the resolution. An offset‐digital‐to‐analog converter/attenuator network is used to slow down the scan rate in the mass‐selective instability mode of operation with reasonance ejection. Attenuations of the scan rate by 200 to 700 times increase the resolution from 500 (with no attenuation) to 40 000 and 100 000 (full width at half maximum), respectively, for the [M + H]+ peak of substance p (m/z 1348). These improved resolutions are achieved in experiments which use resonance ejection to extend the mass‐to‐charge range.
The electron‐induced fragmentation of large ring cycloalkylamines. Intramolecular reactions between radical and immonium within distonic ions
Authors: Boukobbal B. , Lefèvre O. , Longevialle P. , Bouchoux G.
Published: May 2005

The unimolecular reactivity of molecular radical cations of secondary and tertiary cycloalkylamines in the gas phase is explained by the reactivity of the radical. Two competing reactions are crucial: the displacement of the radical along the hydrocarbon chanin by hydrogen transfers leading to a series of distonic ions, and the reaction of the radical with the immonium group, in each distonic ion, leading to cyclic structures. The resulting rearranged parent ions fragment subsequently by losing homelogous alkyl radicals.
Ethane elimination from C11H isomers. The effect of the position of formation of the neutral in relation to the ionic partner on the competitiveness of ion/neutral complex‐mediated eliminations
Authors: McAdoo David J. , Hudson Charles E. , Longevialle P.
Published: May 2005

Competition between loss of ethyl and ethane elimination through [C2H˙5 C9H] complexes is assessed as a function of the initial location of the two partners relative to each other. Ethyl loss is favored when that species originates from near the end of the chain, but ethane elimination increases steadily in relative importance as the site of cleavage is shifted towards the middle of the chain and is dominant when the ethyl is cleaved from the middle carbon. It is speculated that when the center‐of‐charge and the center‐of‐mass of the complex are substantially away from each other, individual rotation of the partners causes the ethyl group to spend relatively litle time near the hydrogen atoms it can abstract, favoring simple dissociation over ethane elimination. When the two centers approximately coincide, it is supposed that the ethyl group spends much of its time near abstractable hydrogen atoms, favoring ethane elimination.
On the formation of rotationally hot H by dissociation of CH dications
Authors: Krishnamurthi Vidhya , Mathur D. , Evans G. T. , Harris Frank
Published: May 2005

Dissociation of CH into CH ion pairs results in formation of H ions possessing a degree of rotational excitation which is high enough to enable formation of several rotational resonance states. These resonances give rise to unimolecular dissociation into H+ + H· fragments. Ion translational energy spectrometry has been applied to measure such dissociation spectra, and a number of rotational resonances are observed. Rotational resonances are not observed when H ions are generated from H2 precursors. Two models based upon ideas of impulsive energy release are investigated which attempt to correlate the centre‐of‐mass kinetic energy released upon dissociation of CH with the observation of the rotational resonances. There is good accord between the experimental results and the prediction of our models.
On the structure of [C9H6O]+· ions originating by electron impact induced decomposition of chalcone
Authors: Ardanaz C. E. , Kavka J. , Curcuruto O. , Traldi P. , Guidugli F. , Somogyi Arpad
Published: May 2005

The electron impact induced fragmentations of chalcone have been studied with the aid of high resolution measurements, using metastable decompositions by linked scans and mass‐analysed ion kinetic energy spectroscopy through collisional experiments by ion‐trap mass spectrometry and labellng by 13C deuterium. Based on the data obtained, two different mechanisms for the formation of m/z 130 ions have beenproposed.
Quantitative analysis of the molecular species of monosialogangliosides by continuous‐flow fast‐atom bombardment mass spectrometry
Authors: Chen S. , Pieraccini G. , Moneti G.
Published: May 2005

Negative‐ion continuous‐flow fast‐atom bombardment mass spectroemtry was evaluated asa means for the quantitative analysis of N‐acetylneuraminyl‐galactosyl‐glucosyl ceramide (NeuAc‐G) and N‐acetylgalactosaminyl‐(N‐acetylneuraminyl)galactosyl‐glucosyl‐ceramide (NeuAc‐G). This study was carried out on a 7070‐EQ mass spectrometer (VG Analytical, Manchester, UK) using a home‐made continuous‐flow fast‐atom bombardment probe with a mixture of methanol +water+triethanolamine (70:27:3, v/v/v)as the mobile phase. Utilizing 100 ng of acetyl‐lysogalactosyl‐N‐acetylgalactosaminyl‐(N‐acetylneuraminyl)galactosyl‐glucosylceramide (acetyl‐lysoG) as an internal standard curves for NeuAc‐GM3 d18:1‐16 0, NeuAc‐G d18:1‐18:0 and Neuac‐G d18:1‐18:0 were found to be linear over the range 5‐250ng, with associated correlation coefficients of 0.990‐0.997. The lower limit of detection was found to be 2.5ng. Satisfactory results could also de obtained when the calibration curves were derived from the deprotonated molecular ions of a mixture of the NeuAc‐ and NeuAc‐G classes. Using this approach, quantitative determination of NeuAc‐G d18:1‐16:0 from rat adrenal gland was performed sing N‐acetylneuraminic acid assay as a test control. We found 278±36 ng of this species in 1 mg of tissue (three replicate experiments). The procedure represents a senstive method for the quantitation of mionosialogangliosides and its capability to give molecular species information.
Fuzzy classificational analysis of continuously scanned mass spectra of binary mixtures of positionally isomeric tetradecnols
Authors: Gu Yuan , Hirano Chisato , Horiike Michio
Published: May 2005

Binary mixtures of positionally isomeric tetradecenols were by conventional combined gas chromatography/mass spectrometry without any chemical modification. Each spectrum in repetitive scanning was interpreted in terms of similarity of mass spectral patterns based on a fuzzy classification. This methodology is used for the rapid analysis of chromatographically unresolved isomers in a mixture.
Plotting mass‐peak profiles from selected‐ion recording data
Authors: Grange Andrew H. , Brumley William C.
Published: May 2005

Plotting of mass peak profiles at high mass resolution for chromatographic peaks of low ion abundance is possible from single‐ion monitoring data due to the high sensitivity and low cycle time for single‐ion monitoring. The mass profiles provide accurate masses, document mass resolution at a mass as a chromatographic peak elutes and provide relative abundances for two ions at the same nominal mass. A personal computer is used to plot the mass peak profiles.
Fragmentation studies of peptides: The formation of Y ions
Authors: Kenny Peter T. M. , Nomoto Kyosuke , Orlando Ron
Published: May 2005

The mechanism for the formation of y ions in the collision‐induced dissociation (CID) spectra of protonated peptides produced by fast‐atom bombardment was investigated by tandem mass spectrometry and deuterium labelling studies. The results show that a hydrogen atom attached to nitrogen and not to carbon migrates during cleavage of the amide bond. A mechanism based on these results is presented.
Analysis of a mass‐analyzed ion kinetic energy profile. I. Analytical expression for a peak shape at a single kinetic energy release
Authors: Yeh In Chul , Kim Soo
Published: May 2005

An analytical expression has been derived for the mass‐analyzed ion kinetic energy spectral profile resulting from a single kinetic energy release in a metastable ion decopmposition. Effects of the Z and Y discriminations and the site of dissociation on the peak‐shape have been accounted for. In addition an analytical peak‐shape function has been derived for a dissociation occurring in and near the collision cell floated at high voltage. Excellent agreement between the present results and the peak shapes obtained by regorous ion‐optical trajectory calculations support the validity of the present method. More importantly, the present method has the advantage of a tremendous reduction in computing time.
The extent of internal excitation of the protonated molecules of some liquid martices bombarded by keV Cs+ ion beams
Authors: Hamdan M.
Published: May 2005

In an attempt to probe the extent of internal excitation of protonated ions formed by positive fast‐ion bombardment, the protonated molecules of four commonly used liquid matrices are formed by means of the above technique and their respective mass‐selected collision‐induced dissociation (CID) spectra are investigated within the collision energy range, 5‐200 eV (in the laboratory frame of references). These measurements are also repeated for the same four precursor ions formed by means of positive‐ion chemical ionization in two different reagent gases, NH3 and CH4. The observed dissociation channels and the relative peak heights associated with them imply that the internal excitation of protonated molecules formed by fast‐ion bombardment is much higher than that associated with the protonated ions formed in positive‐ion ammonia CI(NH3‐CI+). On the other hand, close resemblance between the CID spectra of ions formed by the first technique, by CH4‐CI+ and by electron ionization is clearly evident.
A compact time‐of‐flight mass spectrometer for the structural analysis of biological molecules using laser desorption
Authors: Cornish Timothy , Cotter Robert J.
Published: May 2005

A compact laser‐desorption time‐of‐flight mass spectrometer using a 600 ps nitrogen laser and 1 Gsample/s transient recorder is described. The instrument incorporates two electrically‐isolatable, reflecting flight tubes designed for subsequent configuration of the mass spectrometer as a tandem instrument. In this first report, we compare mass resolution in the laser‐desorption mass spectra of an organic dye, sinapinic and caffeic acid matrices, and sevesral small peptides. For directly desorbed ions, peak widths are generally of the order of 11 to 13 ns, so that mass sesolutiojn increases with increasing mass. For peptide ions in the range of 500 to 1000 u, formed by matrix‐assisted desorption, peak widths range from 9.5 to 17.6 ns and increase with mass. However, better than unit mass resolution (1600 to 2400) is maintained throughout this range. Mass measurement accuracy is better than 0.1 u using a single calibration peak and a prompt start trigger pulse. Prospects for extending mass range and resolution are discussed.
The components of the venom of a spider Scodra griseipes. 1. Analysis of low molecular weight products using gas chromatography/mass spectrometry
Authors: Lange C. , Paris C. , Clerier M.‐L.
Published: May 2005

Low molecular weight venom constituents of the spider Scodra griseipes have been derivatized using bis(trimethylsilyl)‐trifluoracetamide and pentafluoropropionic anhydride. Examinatio of these derivatives by coupled gas chromatogrtaphy/mass spectrometry using electron ionization or ammonia‐ or isobutane‐chemical ionization allows their structural identification. Comparisons have also made with retention time and mass spectra of the pure compounds. Four acids: phosphoric, lactic, citric, Y‐aminobutyric (neurotransmitter0 and four basic biogenic amines: putrescine, cadaverine, spermidine and spermine have been found.
Improvements in ion‐trap chemical‐ionization performance
Authors: Cairns Thomas , Chiu Kin S. , Siegmund Emil , Weber Michael
Published: May 2005

Ion‐trap chemical‐ionization performance has been imporved by application of a modified scan function for the rejection of the undesired electron‐ionization‐like (EI‐like) ions formed at the beginning of the reaction ionization period. The net effect of this software modification to the automatic reaction control is to produce chemical ionization (CI) spectra that are no longer adulterated with conventration‐dependent EI‐like ions. Under such improved conditions, CI spectra from an ion trap can now be dirctly compared with CI spectra produced on conventional quardrupole and magnet‐scanning instruments.
Differences in the conformational state of a zinc‐finger DNA‐binding protein domain occupied by zinc and copper revealed by electrospray ionization mass spectrometry
Authors: Huthens T. William , Allen Mark H. , Lewis I.
Published: May 2005

Transition metal ions are important in biological regulation partly because they can bind to and stabilize protein surface domain structures in specific conformations that are involved in key molecular recognition events. There are twso C2‐C2 type zinc‐finger sequences within the highly conserved DNA‐binding domain of the estrogen receptor protein (ERDBD). Electrospray ionization (ESI) mass spectrometry has been used to demonstrate that the metal‐binding sites within the 71‐residue ERDBD can bind either Zn (up to 2) or Cu (up to 4). Evidence for the induction and /or stabilization of a different conformational state with bound Cu is revealed by a characteristic shift in the ESI charge envelope. The 10+ charge state is most abundant for the fully reduced ERDBD apopeptide and the ERDBD‐Zn holopeptide (bound Zn does not alter the charge envelope. In contrast, the 8+ charge state is typically the optimjum charge state observed for the ERDBD‐Cu holopeptide; indeed, the entire charge envelope is frame‐shifted to lower charge states with bound Cu. Interpretation of the altered charge states is simplified because (i) a single type of metal‐binding ligand (sulfur) is involved in the case of both Zn and Cu binding, and (ii) the two different metal cations are both divaalent. Thus, it is likely that the dissimilar charge envelopes represent different peptide conformers, each of which is stabilized by a different type of bound metal ion. The covalent bridging or adjacent Cys residues within a peptide is similar to the formation of intramolecular disulfide bonds, a process that we also found to decrease both the optimum and mumber of ERDBD charge states observed by ESI. The existence of distinct conformational states for the ERDBD‐Zn and ERDBD‐Cu is consistent with the differences in apparent coordinate covalent geometry and stoichiometry for the two bound metal ions. Our findings are aslo consistent with prevous investigations of globular proteins that reveal an increase both in the number of charge states and a shift in the optimum charge state when structure is disrupted by reduction of intramolecular disulfide bonds.
Atmospheric‐pressure ionization interface for a bench‐top quadrupole ion trap
Authors: Mordehai Alex V. , Hopfgartner Gerard , Huggins Tom G. , Henton Jack. D.
Published: May 2005

A novel interface is described that effects the sampling and mass analysis of ions formed at atmospheric pressure into a Saturn II bench‐top quadrupole ion‐trap mass spectrometer. The standard high‐vacuum pumping system of the system is unchanged, bit a 960L/min rotary pump is incorporated to pump the first vacuum stage of the atmospheric‐pressure ion sampling interface. An ‘Electric skimmer’ ion focusing region in the first vacuum turbomolecular pump of the Sasturn II maintains high vaccuum at 4×10−4 Torr in the analyzer region while helium damping gas is introduced. By vaarying the potential difference between selected lenses in the first vacuum region the ‘declustering’ energy may be varied to decluster effectively ion/molecule dissociation mass spectra. The on‐line analysis of quaternary ammonium drugs by liquid chromatography of 5 ng and 150 pg, respectively.
Charge‐state distributuion and electric‐discharge suppression in negative‐ion electrospray mass spectrometry using/chlorinated solvents
Authors: Cole Richard B. , Harrata A. Kamel
Published: May 2005

Solvent effects in electrospray mass spectrometry performed in the negaative‐ion mode have been examined, for a series of low‐nucleophilicity chlorinated solvents. The charge‐state distribution of a test analyte was observed to change radically with the nature of the solvent. Formation of anions of higher charge stae was favored in solvents of higher polarity. The shift in the charge‐state distribution has been largely attributed to improved solvation of chaarge sites by increasingly polar solvents. Evidence suggests that valence electrons of the chlorine atoms do not contribute significantly to solvation of acidic protons. Highly chlorinated solvents in teh electrospray bath gas serve to suppress electrical (corona) discharge phenomena. The latter effect was magnified with increasing percent weight of chlorine in the solvent. The observed discharge suppression has been attributed to electron‐capture preocesses. This solvent effect was muted when a highly efficient electron seavenger(i. e., SF6) comprised the elctrospray high gas.
Determination of 15N enrichment of taurine in cat urine by high resolution fast‐atom bombardment mass spectrometry
Authors: Stämpfli Andress A. , Ballèvre Olivier , Fay Laurent B.
Published: May 2005

A method is described for measuring the stable isotopic enrichment of taurine in cat urine samples by high resolution fast‐arom bombardment mass spectrometry, after 15N labelled taurine was given to cats for the purpose of investigation taurine metabolism. The 15N enrichemnt of taurine was measurd after hydrolysis and purification of taurine by anion/cation exchange chromatography. The isotopic ratio of taurine was detemined by measuring the [M+H]+ ion peaks in the spectra of the unlabelled and labelled compounds under multiple ion scan conditions. The overall standard deviation of the measurement is beter than 4%. This method requires no derivation and uses only 500 μL of urine samples.
Data transfer from a DEC PDP‐11 based mass spectrometry data station to an MS‐DOS personal computer
Authors: Raffaelli Andrea , Bruins Andries P.
Published: May 2005

This paper describes a simple procedure for obtaining better quality graphic output for mass spectrometry data from data systems equipped with poor quality printing devices. The procedure uses KERMIT, a low cost public domain software, to transfer ASCII tables to a MS‐DOS personal computer where they can be elaborated and customized using one of the powerful graphic tools available. The final result can be sent to a high quality laser printer or pen plotter or incorporated in a document generated with a word processor.
Mass spectrometry of DNA mixtures by laser ablation from frozen aqueous solution
Authors: Schieltz David M. , Chou Chau‐Wen , Luo Cong‐Wen , Thomas Robert M. , Williams Peter , Becker C. H.
Published: May 2005

We report time‐of‐fight mass spectra of test mixtures of six single‐stranded DNA segments. The segments range in size from 8 to 60 nucleotides (molecular weight range 2413 to 18 602 Da). The best mass spectra were obtained by pulsed laser ablation of thin frozen films of an aqueous solution of the mixture from an oxidized copper substrate. These mass spectra are dominated by the molecular‐ion peak for each DNA segment, and show little evidence of fragmentation, peak broadening or cluster formation. In contrast, mass spectra obtained using UV laser ablation from an anthranilic acid matrix yield broad peaks with evidence of fragmentation, and DNA segments longer than 26 nucleotides are difficult to detect.
Thermospray high‐performance liquid chromatography/mass spectrometric determination of cyclosporins
Authors: Abián J. , Stone A. , Morrow M. G. , Creer M. H. , Fink L. M. , Lay J. O.
Published: May 2005

The cylic undecapeptides cyclosporin (Csp) A, CspD and dihydro CspC (HCspC) were analyzed by high‐performance liquid chromatography/thermospray‐mass spectrometry (HPLC/TSP‐MS) on line with 1–2 pmol injected on column. Mass spectra were characterized by signals corresponding to the [M + H]+ ion as well as fragment ions derived from he loss of 112 (CspA and CspD) or 44, 114 and 114+44 (HCspC) mass units from the parent ion. The same qualitative profile was observed for negative‐ion acquisition where the ions were formed by proton abstraction. The application of the technique to the characterization of CspA and its major hydroxylated and dealkylated metabolites in human blood samples is presented.
Opimizing signal and mass resolution for matrix‐assisted laser desorption utilizing a linear time‐of‐flight mass spectrometer
Authors: Brown R. S. , Glfrich N. L.
Published: May 2005

Results are oresented for various instrumental configurations employed for matrix‐assisted laser desorption mass spectrometry. Mass resolution is determined for a linear time‐of‐flight mass spectrometer for various lengths of the field‐free region. A wire ion guide is utilized and is shown to improve ion transport efficiencies for longer field‐free regions. It is also determined experimentally that a modest mass resolution increase is often obtained in configurations employing the wire ion guide when compared to the mass resolution obtained with the same geometr without the wire ion guide. Optimal applied potentials are determined for the wire ion guide. No mass dependence on the opitmal applied potential (−100 V) for the wire ion guide is observed for samples of equine myoglobin (MW 16 951.5 Da) and a bacterial protease (MW 27 228.4 Da). The optimal applied voltage was also found to b identical (−100 V) for the singly through quadruply charged molecular ion species of rabbit gamma globulin (MW ≈︁ 150 000 Da). It is shown that a 2 m flight tube with a wire ion guide provides better signal‐to‐noise mass spectra than a 1 m flight tube without the wire ion guide and can more than double the mass resolution obtainable. Utilization obtainable. Utilization of a 4 m flight tube gives minimal mass resolution enhancement at the expense of signal‐to‐noise.
Investigation of some β‐lactam antibiotics by means of 2–35 keV cesium ion bombardment
Authors: Hamdan M. , Curcuruto O. , Tarzia G. , Harris F. M.
Published: May 2005

A number of commercial β‐lactam antibiotics are investigated by means of cesium ion (Cs+) bombardment in the kinetic energy range 2–35 keV. The relative intensities of the protonated molecules, as well as some of the major fragment ions, are monitored as a function of the Cs+ kinetic energy. The dependence of the intact protonated molecule:fragment ion ratios on the primary‐ion kinetic energy is evident in some of the spectra investigated. An attempt is made to interpret these results in terms of existing secondary‐ion mass spectrometry data which have been obtained in a different kinetic energy range.
Matrix‐assisted laser desorption/ionization inside a quadrupole ion‐trap detector cell
Authors: Doroshenko Vladimikr M. , Cornish Timothy J. , Cotter Robert J. , Ross Mark M.
Published: May 2005

An ion‐trap detector has been modified for matrix‐assisted laser desorption/ionization using a pulsed frequency‐quadrupled Nd: YAG laser and extended mass range up to 3300 u using the resonant‐rejection mode of operation. The matric‐assisted laser desorption/ionization mass spectra of a number of peptides are reported, and the effects due to the synchronization of the laser pulses and the phase of the RF voltage applied to the ring electrode are described.