bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactions of Sc+, Ti+, V+, Fe+, Co+ and Ni+ with 1‐fluoronaphthalene in the gas phase. Metal‐catalyzed oligomer formation and observation of unusual ring fragmentation
Authors: Bjarnason Asgeir , Freiser Ben S.
Published: May 2005

Poly(naphthalyne) is of interest, in particular, due to its intrinsic electrical conductivity. Reported here are the initial steps in the metal‐catalyzed polymerization of naphthalene as observed in the gas‐phase reactions of Sc+, Ti+, V+, Fe+, Co+, and Ni+ with 1‐fluoronaphthalene studied in a Fourier‐transform mass spectrometer. Sc+, Ti+, V+, and Fe+ were found to dehydrofluorinate in a sequential fashion up to three neutral fluoronaphthalene molecules to form ions of the form MC10H, MC20H and MC30H, where M represents the metal. Sc+ showed unusual reactivity by also being able to eliminate C2H2 from fluoronaphthalene, and Ti+ was found to eliminate a hydrogen atom to form TiC10H6F+. Second‐ and higher‐order reactions were studied and several ionic products from primary and secondary reactions were investigated by collision‐induced dissociation. Formation of unmetallated ions was also observed. For example, C20H was determined to arise from MFC20H, for M = Ti, V, while for iron it was formed directly from FeC10H in its reaction with the neutral fluoronaphthalene. This is in contrast with the behavior expected from an earlier study of fluorobenzene, where it was observed that (C6H4) species arose from M(C6H4) species.
Deprotonation reactions of multiply protonated ubiquitin ions
Authors: Cassady Carolyn J. , Wronka John , Kruppa Gary H. , Laukien Frank H. , Hettich Robert
Published: May 2005

The gas‐phase deprotonation reactions of multiply protonated ubiquitin ions have been studied in a Fourier‐transform ion cyclotron resonance mass spectrometer. Electrospray ionization was used to generate ubiquitin ions with attachment of 7–13 protons. Rate constants were measured for the reactions of these protein ions with four amines: n‐propylamine, di‐n‐propylamine, tri‐n‐propylamine, and N,N,N′,N′‐tetramethyl‐1,4‐diaminobutane. The gas‐phase basicities of the amines ranged from 210.1 kcal/mol to 232.6 kcal/mol. The rate constants were found to increase as the charge state of the ion increased and as the basicity of the amine increased. Several reactions proceed at near the collision rate and have rate constants in excess of 10−8 cm3 molecule−1 s−1. With the more basic reactants, multiple protons could be stripped sequentially from ubiquitin ions at roughly equivalent rates, suggsting that these protons are attached to sites with similar basicities. In general, deprotonation occurs if the gas‐phase basicity of the amine is within 10 kcal/mol of the intrinsic gas‐phase basicity of the amino acid residue being deprotonated. For [M+nH]n + , n = 4–6, nonlinear pseudo‐first‐order kinetic behavior indicated the presence of multiple ion structures. Kinetic, structural and thermodynamic aspects of these reactions are discussed.
Fragmentation of gold clusters stored in a penning trap
Authors: Becker St. , Dietrich G. , Hasse H.‐U. , Klisch N. , Kluge H.‐J. , Kreisle D. , Krückeberg St. , Lindinger M. , Lützenkirchen K. , Schweikhard L. , Weidele H. , Ziegler J. , Nibbering N. M. M.
Published: May 2005

The collision‐induced dissociation of positively charged gold clusters (2–23 atoms) stored in a Penning trap has been studied. After collisions with rare gases, excited clusters predominantly decay by emission of one or two atoms. The loss of two atoms occurs most probably through the emission of a dimer rather than by a sequential evaporation. The minimum kinetic energies of clusters required to induce dissociation exhibit a pronounced odd–even effect. Clusters with an even number of delocalized electrons are more stable than those with an odd number.
Formation of multiply charged ions from large molecules using massive‐cluster impact
Authors: Mahoney John F. , Shannon Cornett D. , Lee Terry D. , Barofsky Douglas F.
Published: May 2005

Massive‐cluster impact is demonstrated to be an effective ionization technique for the mass analysis of proteins as large as 17 kDa. The design of the cluster source permits coupling to both magnetic‐sector and quadrupole mass spectrometers. Mass spectra are characterized by the almost total absence of chemical background and a predominance of multiply charged ions formed from 100% glycerol matrix. The number of charge states produced by the technique is observed to range from +3 to +9 for chicken egg lysozyme (14 310 Da). The lower m/z values provided by higher charge states increase the effective mass range of analyses performed with conventional ionization by fast‐atom bombardment or liquid secondary ion mass spectrometry.
The complexation and chiral selectivity of 2‐hydroxypropyl‐β‐cyclodextrin with guest molecules as studied by electrospray mass spectrometry
Authors: Haskins Neville J. , Saunders Martin R. , Camilleri Patrick , Games David E.
Published: May 2005

Electrospray mass spectrometry has been used to study the complexation of ‘guest’ molecules with a mixture of hydroxypropyl‐substituted β‐cyclodextrin derivatives. In all cases studied, the predominant derivative was shown to contain a maximum of seven hydroxypropyl groups, most probably related to alkylation of each of the seven glucose units of the parent β‐cyclodextrin. Chiral selectivity was not observed for D‐ and L‐phenylalanine methyl esters. In contrast D‐propranolol and L‐tryptophan methyl ester formed stronger complexes than the corresponding L‐ and D‐enantiomers, respectively. Molecular modelling studies were also carried out, in an attempt to identify the factors that can play a part in determining the mechanism of the observed non‐covalent interactions.
High temperature mass spectrometric study of 3Al2O3 · 2SiO2
Authors: Schornikov S. I. , Stolyarova V. L. , Shultz M. M.
Published: May 2005

The high‐temperature Knudsen effusion method was used to study the vaporization processes and thermodynamic properties of mullite from 1833 K to 2033 K. Data on the activities of Al2O3 and SiO2 and on the entropy, enthalpy and Gibbs energy of formation of mullite were obtained. It was shown that the atomization energy of the AlSiO gaseous molecule (1062±25 kJ/mol) is close to the values that have been obtained earlier.
Chromatographic and mass spectrometric methods for the identification of phosphorylation sites in phosphoproteins
Authors: Hunter Ann P. , Games David E.
Published: May 2005

The phosphorylation sites in a model phosphoprotein, αsl‐casein from bovine milk, have been identified by tryptic peptide mapping (Gibson and Cohen, Methods Enzymol. vol. 193, p. 480 (1990)) employing reversed‐phase high performance liquid chromatography (RPHPLC)/electrospray ionization mass spectrometry (ES‐MS); by infusion tandem mass spectrometry (MS/MS) and LC/MS/MS in neutral loss mode of tryptic digests of αsl‐casein, in which the characteristic neutral loss of phosphoric acid by phosphopeptides under collision‐induced dissociation (CID) conditions is exploited to highlight phosphopeptides in a tryptic digest (Covey et al., in Methods in Protein Sequence Analysis, Jörnvall et al. (Eds), Birkhäuser Verlag, Basel 1991), and by a novel method, termed LC/CID‐MS, in which phosphopeptides are located in mixtures of peptides by the generation and detection of phosphate‐specific fragment ions during LC/ES‐MS (Huddleston et al., J. Am. Soc. Mass Spectrom. vol. 4, p. 710 (1993)). An appraisal of the efficiency, sensitivity and practicality of each of these methods in the identification of phosphorylation sites in post‐translationally modified proteins is given.
Determination of fumonisins using on‐line liquid chromatography coupled to electrospray mass spectrometry
Authors: Doerge Daniel R. , Howard Paul C. , Bajic Steve , Preece Steve , Games D. E.
Published: May 2005

Fumonisin (FB) mycotoxins are produced by Fusarium monoliforme, which grows primarily on yellow corn. Ingestion of FB1‐contaminated food causes leukoencephalomalacia in horses, pulmonary edema in pigs, and is suspected in the etiology of human esophageal cancer. Chromatographic separation and detection of underivatized fumonisins has been hampered because these compounds are nonvolatile, thermally labile, and devoid of chromophoric functional groups. We report here a simple liquid chromatography/mass spectrometry method employing chromatographic separation on a polymer‐based column coupled with sensitive detection using positive‐ion electrospray mass spectrometry for the quantification of fumonisins B1, B2 and B3 in extracts of commercial corn meal.
Mass determination of human immunoglobulin IgM using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Nelson Randall W. , Dogruel David , Williams Peter , Beavis Ronald
Published: May 2005

Monoclonal human immunoglobulin IgM has been analyzed using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. Using a matrix of sinapinic acid with a laser wavelength of 355 nm, positive ions with 2 to 6 charges were observed in the mass spectra. Two major molecular species were present. The molecular weights estimated from the multiply‐charged signals were found to decrease systematically with decrease in the charge state of the ion. This effect was determined to stem from the non‐linear influence of the initial kinetic energy of desorption on the final kinetic energy of the multiply‐charged species. A method of successive approximations, with the molecular weights and desorption velocities of the analytes as variables, was used to correct for these non‐linearities. Mean molecular weights for the two IgM species were found to be 939 000 ± 2000 and 982 000 ± 2000 Da. An initial desorption velocity of 565 ± 10 ms/s was determined for both.
Rearrangements of doubly charged acylium ions from lysyl and ornithyl peptides
Authors: Tang Xue‐Jun , Boyd Robert K.
Published: May 2005

The study of large‐scale rearrangements of [b′]2+ ions produced by electrospray ionization of Substance P (Tang et al., Anal. Chem. Vol. 65, p. 2824 (1993)) has been extended to 18 other peptides containing either a lysine or ornithine residue remote from the C‐terminus. Evidence for wholesale transfer of one or more residues, from the C‐terminus of the [b′]2+ precursor to the ω‐amino group of the Lys (or Orn) residue, was observed for 12 of the 18 peptides studied. Unfortunately, no rigorous predictive rules, relating features of the peptide sequence to the propensity to undergo such rearrangements, could be discerned although a significant correlation with presence of a proline residue dose to the lysine or ornithine on the C‐terminal side was apparent. The resulting mass‐shifts can complicate derivation of peptide sequences from fragment‐ion spectra of [M+2H]2+ peptide ions, for example, since the cyclized [b′]2+ ions responsible for the rearrangements are readily formed as intermediate species in the fragmentation mechanisms.
Formation of pentavalent silicon anions, (CH3O)2Si(OEt) and CH3OSiH(OEt), in the gas phase
Authors: Murthy Vemisetty S. , Miller Jack M.
Published: May 2005

We describe the formation of pentavalent silicon anions, (CH3O)2Si(OEt) and CH3OSiH(OEt), by a ligand exchange and a hydride reaction in the presence of argon buffer in the gas phase. A simple elimination is followed by double and triple cyclic elimination mechanisms, during the collision‐induced dissociation of CH3OSiH(OEt).
Investigation of ruthenium (II) and iron (II) tris‐bipyridyl complexes by means of 10–30 keV Cs+ ion bombardment and collision‐induced dissociation
Authors: Bignozzi Carlo A. , Bortolini Olga , Curcuruto Ornella , Hamdan Mahmoud
Published: May 2005

[Ru(bpy)3(X)2] and [Fe(bpy)3(X)2] complex salts (bpy=2,2′bipyridine; X = ClO, PF, Cl−) were investigated by means of Cs+ fast‐ion bombardment and mass‐selected collision‐induced dissociation (CID). A number of dissociation channels which can be attributed to the loss of intact counterions, bpy neutral ligands and to the insertion of formal O, fluoride or chloride from the counterions ClO, PF, Cl− are evident in both the fast‐ion bombardment and CID spectra. Formation of doubly charged intact cations is also observed for all the compounds investigated. The relative intensities of the major desorbed ions are monitored as a function of the Cs+ kinetic energy in the range 10–30 keV.
Laser desorption/gas‐phase ionization of the amino acid tryptophan
Authors: Reilly Peter T. A. , Reilly James P.
Published: May 2005

A solution of tryptophan, rhodamine B and glycerol is irradiated in the source region of a time‐of‐flight mass spectrometer by visible light from a pulsed laser. Tryptophan and rhodamine B are desorbed and subsequently ionized by a second pulse of ultraviolet light. The observed mass spectra and dependence of ion yields on time delay between light pulses provide information about the laser desorption process.
Exact fields in multi‐electrode ion optics
Authors: Reuben Andreas J. , Radchik Alex V. , Smith Geoffrey B. , Vagov Alex V.
Published: May 2005

The exact determination of electrostatic potential is vital in specifying the resolution in ion‐beam focusing devices such as quadrupole mass spectrometers (QMS). Current numerical routines are marked by poor convergence on boundaries and become unwieldy when the number of electrodes, 2n, is greater than four, or when the structure is modified. Using a conformal transformation we have succeeded in finding the exact electrostatic potential distribution everywhere within a QMS which contains four cylindrical electrodes. All the coefficients in the multipole expansion of the potential are readily calculated. The boundary value problem is solved by matching coefficients on the electrode surface, which is a circle embedded in the transformed coordinate frame. We have proven that for every allowed position of the electrode centre, R, there exists a corresponding electrode radius, r, for which the dodecapole term in the potential expansion vanishes. Our analytically obtained relationship between the above‐mentioned parameters differs slightly from that in current use. As these parameters are based on an exact solution, their practical use in mass determination may be considerable.
Characterization of cyclodepsipeptide‐glutathionyl conjugates by negative‐ion fast‐atom bombardment linked‐scan mass spectrometry
Authors: Loutelier C. , Marcual A. , Cherton J.‐C. , Lange C.
Published: May 2005

A cyclodepsipeptide‐glutathionyl conjugate has been analysed for the first time using negative‐ion fast‐atom bombardment linked‐scan mass spectroscopy. Fragment anions produced by collision‐induced dissociation are discussed.
Sequential product‐ion spectra (MS3) with array detection and reaction‐intermediate scanning of a cyclopeptide on a five‐sector mass spectrometer
Authors: Lange C. , Loutelier C. , Bordoli R. S.
Published: May 2005

A new strategy, based on sequential product‐ion spectra (MS2 and MS3) and reaction‐intermediate scanning (MS3), provides a rapid and unambiguous sequence determination of E‐destruxin, a cyclodepsipeptidic toxin from Metarrhizium anisopliae fungus.
Self‐calibrating property of matrix‐assisted laser desorption/ionization time‐of‐flight spectra of polymeric materials
Authors: Montaudo Giorgio , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo , Daolio S.
Published: May 2005

A calibration procedure is introduced, which allows one to obtain absolute mass values in matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) spectra of polymeric materials, thus avoiding ambiguous mass assignments. The method consists in combining the observed times of flight in a function denoted as ‘modified sum of squares’ (SS2) and in finding the point of minimum for SS2. The procedure takes advantage of the finding that SS2 possesses an extremum property, i.e. it takes its minimum at θ, the mass of the first oligomer appearing in the MALDI‐TOF spectrum. The method was tested by recording the MALDI‐TOF spectrum of an aminolyzed Nylon 6 and of a glycolized poly(butyleneadipate) (PBA) sample. Nylon 6 was found to be made of a series of oligomers bearing diaminohexamethylene (DAHM) terminal groups. PBA is made of a series of oligomers with butyleneglycol end‐groups. The intense peaks seen in the mass spectra are due to sodium‐cationized ions, whereas the less‐intense peaks are due to potassium‐cationized ions. The function SS2 was built for the two samples and a point of minimum was found at the point θ = 817.6 for Nylon 6 and at the point θ = 713.6 for PBA. This finding allowed the interpretation of the mass spectra.
3‐aminopicolinic aid as a matrix for laser desorption mass spectrometry of biopolymers
Authors: Taranenko N. I. , Tang K. , Allman S. L. , Ch'ang L. Y. , Chen C. H.
Published: May 2005

3‐Aminopicolinic acid (3‐APA) was tested and found to be a useful matrix for matrix‐assisted laser desorption/ionization of DNA and protein. Single‐stranded DNA segments of 150‐mer and double‐stranded DNA of 246 base pairs were successfully detected by using 3‐APA as an ultraviolet‐absorbing matrix in a linear time‐of‐flight mass spectrometer. In the case of the double‐stranded DNA, only parent ions corresponding to single‐stranded DNA were observed. The comparison with 3‐hydroxypicolinic acid and picolinic acid matrices is discussed.
2‐(4‐hydroxyphenylazo)‐benzoic acid: A solid matrix for matrix‐assisted laser desorption/ionization of polystyrene
Authors: Montaudo Giorgio , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo , Daolio S.
Published: May 2005

Liquid matrices are currently used in matrix assisted laser desorption ionization (MALDI) of non‐polar macromolecules, such as polystyrene. We investigated the possibility of using non‐liquid compounds as matrices. A series of polystyrene samples was analyzed by MALDI using a time‐of‐flight (TOF) analyzer. We found that a solid matrix, namely 2‐(4‐hydroxyphenylazo)‐benzoic acid, yields quality mass spectra. The MALDI‐TOF spectra were used to measure the parameters which characterize the molecular weight distributions of the polystyrene samples. The values obtained by MALDI‐TOF were in good agreement with those obtained by other methods.
Differentiation of bacteria using protein profiles from matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Cain Teresa C. , Lubman David M. , Weber Walter J.
Published: May 2005

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry is demonstrated as a means for rapidly differentiating bacteria based upon their water‐soluble‐protein profiles. The procedure involves release of cell contents by breaking cell membranes using a sonication method, and is performed with minimal sample preparation. Minimal purification of cell contents is required for the procedure. Protein profile signals obtained are found to be enhanced greatly by the use of a Nafion substrate.
A new mass spectrometric approach to detect modifications in DNA
Authors: Janning Petra , Schrader Wolfgang , Linscheid Michael , Baillie T. A.
Published: May 2005

A new approach is described for the enzymatic digestion of DNA yielding oligonucleotides ranging from dinucleoside monophosphates to octanucleoside heptaphosphates. DNA was digested by means of the benzon nuclease, an unspecific nuclease, and alkaline phosphatase to remove the terminal phosphate. The mixture of oligonucleotides was separated using capillary‐zone electrophoresis with a buffer system, yielding a rather strong electro‐osmotic flow. The oligomers are separated into groups with nucleotides of the same chain length. The separation capillary was used as the innermost capillary of an electrospray spraying system. Negative molecular ions of the nucleotides were recorded using a home‐built interface and ion source for a sector‐field mass spectrometer. This approach allows the facile detection of DNA modifications since they lead not only to differences in mass, but also can possess altered electrophoretic mobility. For modifying reactions which exhibit sequence specificity, the information is retained in the oligomers. Thus, reactions of DNA with electrophiles can be evaluated at different levels, since in longer chains, even complex sequence specificity may be apparent. Results from calf thymus DNA digests and preliminary experiments with DNA adducts with styrene oxide are discussed.
Long‐distance stereochemical effects in deprotonated epimeric androstanediols in tandem mass spectrometry
Authors: Garcia P. , Popot M. A. , Fournier F. , Tabet J.‐C.
Published: May 2005

Tandem mass spectrometry in negative‐ion mode using ammonia as reagent gas has contributed to the differentiation of polyhydroxysteroids and to the study of stereochemical effects. The present study provides additional examples of sterochemical effects. A first observation of intramolecular OH− catalysis yielding stereospecific H2O elimination is proposed.
Evaluation of glycosylation site heterogeneity and selective identification of glycopeptides in proteolytic digests of bovine α1‐acid glycoprotein by mass spectrometry
Authors: Hunter Ann P. , Games David E.
Published: May 2005

Glycosylation sites in bovine α1‐acid glycoprotein (AGP) have been identified, and the inherent heterogeneity evaluated, by capillary electrophoretic and reversed‐phase liquid chromatography/electrospray‐mass spectrometric analyses of proteolytic digests of this glycoprotein. The success of these methods in locating glycopeptides relied on significant heterogeneity within each glycosylation site. In order to rapidly locate sites in glycoproteins of any degree of heterogeneity, a novel mass spectrometric method was applied to selectively identify the glycopeptides in a proteolytic digest of bovine α1‐AGP. The glycopeptides were selectively located by the generation and detection of characteristic oxonium ions from the carbohydrate moieties by collision‐induced dissociation (CID) during liquid chromatography/electrospray‐tandem mass spectrometry, and liquid chromatography/CID mass spectrometry, in which fragmentation was induced in the supersonic expansion region of the electrospray source.
Electron ionization mass spectra and metastable‐ion studies on some dicyanoquinonediimines
Authors: Martin Nazario , Seoane Carlos , Garin Javier , Orduna Jesús
Published: May 2005

The 70 eV mass spectra of dicyanoquinonediimine and several derivatives have been studied by accurate mass measurements and metastable‐ion analysis. Characteristic fragmentations of quinone structures and cleavages involving cyanide rearrangement are responsible for most of the total ion current.
Metal‐ion attachment to non‐polar polymers during laser desorption/ionization at 337 nm
Authors: Mowat Ian A. , Donovan Robert J.
Published: May 2005

The attachment of metal ions to non‐polar polymers is shown to be readily achieved using 337 nm laser desorption and ionization, with time‐of‐flight mass analysis, and could thus prove useful for the analysis of such polymers using commercially available matrix‐assisted laser desorption/ionization instruments. Attachment of Cr+, Cu+ and Ag+ has been used successfully to increase the ion yield of polystyrene and polybutadiene during laser desorption/ionization. The metal ion used may originate from the metal sample holder substrate on which the polystyrene is placed, or from metal salts mixed with the polystyrene either prior to placement on the sample holder or in situ. Results have been obtained which illustrate metal‐ion attachment to the polystyrene from the substrate and from a dopant salt simultaneously and the roles of each of these will be discussed.
Polymer molecular weight distribution: Results from matrix‐assisted laser desorption ionization compared with those from gel‐permeation chromatography
Authors: Lehrle Roy S. , Sarson Deborah S.
Published: May 2005

A sample of poly(methyl methacrylate) (PMMA), of which the molecular weight was known from light‐scattering measurements, was subjected to gel‐perrneation‐chromatographic analysis, and the resulting Weight versus log molecular weight (MW) plot was converted by suitable computation to a Number versus linear MW plot. This could then be compared directly with the matrix‐assisted laser desorption ionization MW distribution results obtained for the same sample. The MW distributions obtained by the two methods were significantly different. Two explanations for the discrepancy are offered.
Relationship of Fourier transforms to isotope distribution calculations
Authors: Rockwood Alan L.
Published: May 2005

Isotope distributions of molecules are the result of convoluting elemental isotope distributions multiple times. They are usually calculated using a polynomial expansion method. The present paper starts with the polynomial expansion and shows how to cast the problem in terms of Fourier transforms. Because discrete Fourier transforms can be calculated very efficiently, this new way of looking at the problem has significant practical implications. Specifically, it leads to faster ways to calculate isotope distributions.
Investigation of ‘ghost’ peaks caused by non‐linear fields in the ion trap mass spectrometer
Authors: Mo Wenjun , Langford Marian L. , Todd John F. J.
Published: May 2005

Mass spectral ‘ghost peaks’ are generated with the ion trap by the superposition of higher order multipole fields which originate through deviations from the pure quadrupole field. In data acquisition, when the amplitude of the RF voltage is ramping though a non‐linear resonance point (q*) on the Mathieu stability diagram, some ions (m0) are ejected by the non‐linear field rather than by the quadrupole field at qz=0.908 on the βz=1 boundary. The prematurely ejected ions will be seen as a peak at m1=(q*/0.908)m0, which we have termed a ‘ghost peak’.
AC corona‐discharge aerosol‐neutralization device adapted to liquid chromatography/particle beam/mass spectrometry
Authors: Wilkes Jon G. , Freeman James P. , Heinze Thomas M. , Lay Jackson O. , Vestal Marvin L.
Published: May 2005

An AC corona‐discharge device was inserted upstream of a thermospray vaporizer tip in a liquid chromatography/particle beam mass spectrometer to neutralize static aerosol charging. Response of a test analyte was measured with or without discharge initiation. If the solvent contained no ammonium acetate buffer, increased analyte signal was associated with the discharge. However, in the presence of ammonium acetate the benefit of AC discharge neutralization was either not observed or was more subtle. This led to the conclusion that the previously observed ammonium acetate “carrier” effect is attributable, at least in part, to neutralization of static electric charges produced spontaneously during the solvent nebulization process. In a second experiment, the pattern of particles issuing from the system momentum separator was examined by aiming the particle beam at a cold target located within a mass spectrometer ion source. Variations in particle density were observed depending on (i) whether or not the aerosol had been neutralized and (ii) the proximity of electron‐beam‐collimating magnets to the particle beam trajectory. These results are consistent with a hypothesis that electrostatic charging occurs spontaneously during the nebulization process in which an aerosol is formed from the high performance liquid chromatography effluent. Such electrostatic charging introduces a factor likely to degrade system performance by at least two modes: through interactions of the charged aerosol particles (i) with the walls of the aerosol transmission pathway, and, after they are accelerated into a particle beam and introduced into the mass spectrometer, (ii) with the magnets used for electron beam collimation in many mass spectrometer ion sources.
Reduction of aromatic fluorine compounds in fast‐atom bombardment mass spectrometry
Authors: Aubagnac J. L. , Gilles I. , Claramunt R. M. , Escolastico C. , Sanz D. , Elguero J.
Published: May 2005

The second example of F/H reduction of a fluorine aromatic derivative in a fast‐atom bombardment mass spectrometric experiment is described. It concerns a tetrafluorophenyl derivative bearing two 3,5‐dimethylpyrazol‐1‐yl substituents.
Unusual cross‐ring SN2 reactions of [MH]− ions of methoxyacetanilides
Authors: Blanksby Stephen J. , Dua Suresh , Bowie John H.
Published: May 2005

Deprotonated o, m‐, and p‐methoxyacetanilide show pronounced peaks in their collision‐induced tandem mass spectra (MS/MS) produced by losses of the elements of C2H6. It is proposed that this reaction is a ‘cross‐ring’ internal SN2 reaction involving an incipient methyl anion. For example, p‐CH3OC6H4−COCH3→ [(p‐CH3OC6H4NCO)CH]→−OC6H4NCO+C2H6.
A molecular ion source based on spontaneous desorption
Authors: Schoppmann Christopher , Brandl Dieter , Tomaschko Christoph , Schurr Matthias , Voit Helmut
Published: May 2005

A novel molecular ion source based on the spontaneous desorption process has been investigated. The results obtained indicate that it is well suited for the analysis of organic molecules with masses up to 103 u in a time‐of‐flight mass spectrometer.
Gas phase acetylation of C60 and C70 by ion/molecule reactions
Authors: Liu Ziyang , Hao Guolun , Guo Xinghua , Liu Shuying
Published: May 2005

Gas phase reactions of C60 and C70 with the ion system of acetone under chemical ionization conditions have been studied. C60 and C70 can react with acetyl and oxonium ions, which come from self‐chemical ionization of acetone, to form adduct ions. In addition, C60 and C70 can accept protons to produce protonated ions. C70 is more active in the above reactions than C60 because of its stronger gas‐phase basicity. A σ‐bond between C60 and an acyl carbon atom can be formed to produce stable acetylated C60 ions. The above results may be relevant to the acetylation reactions of C60 in the condensed phase.
A new method for the determination of iron oxidation states by resonant and non‐resonant ionization mass spectrometry
Authors: Maunit B. , Hachimi A. , Calba P. J. , Krier G. , Muller J. F.
Published: May 2005

Different compositions of micrometric particles of powdered iron oxides (Fe1−xO, Fe3O4 and Fe2O3) are examined by time‐of‐flight laser microprobe mass spectrometry. The positive‐ion cluster distributions show a strong correlation with the stoichiometry of iron in the oxide. This correlation is more striking when the resonant process of iron at 293.7 nm is used. The bond dissociation energy of Fe–‐O in the bulk Fe1−xO also affects the intensity distributions. It is very important to study and to identify the iron oxides because they could play a role in the toxicity of certain molecules which could be removed on the oxides.
Mass spectral fragmentation patterns of some new benzo[b]thiophene‐ and thieno[2,3‐b]thiophene‐2,5‐dicarbonyldichlorides and ‐dicarbonyldianilides and anilidoquinolones
Authors: Karminski‐Zamola Grace , Dogan Jasna , Boykin David W. , Bajić Miro
Published: May 2005

The electron impact mass spectra of some benzo[b]thiophene‐ and thieno[2,3‐b]thiophene‐2,5‐dicarbonyldichlorides, 2,5‐dicarbonyldianalides, 9‐anilido‐benzo[b]thienyl[2,3‐c]quinolones and 9‐anilido‐thieno[4,5‐b′]thienyl[2,3‐c]quinolones are discussed. Dominant peaks in dianilides are formed by cleavage of the CN bond on one side of the anilido group, as well as on the anilido group itself in anilidoquinolones. These ions fragment further by the cleavage of a CC bond in dianilides and the CONRPh group is lost directly, while the quinolonic part of the molecule in quinolones fragments with low probability. Characteristic fragment ions of dicarbonyldichlorides arise by the cleavage of the CCl bond.
Intra‐ and interannular substituent migration and intramolecular ipso substitution of biphenyl derivatives in mass spectrometry
Authors: Tu Ya‐Ping , Liu Ya‐Qin , Liu Shu‐Ying
Published: May 2005

Biphenyl derivatives undergo extensive intraannular substituent migrations and subsequent intramolecular ipso substitutions giving rise to a fluorenyi cation and a biphenylene radical cation as common products in mass spectrometry. For biphenyls bearing an alkyl group, interannular substituent migration resulting in a substituted tropylium ion is also observed. Electron‐withdrawing groups are found to be much more favourable to these reactions than the electron‐donating ones.
Identification of novel nucleotides found in the red seaweed Porphyra umbilicalis
Authors: Newton Russell P. , Kingston Eric E. , Overton Alan
Published: May 2005

Extracts of the red seaweed Porphyra umbilicalis are a valuable constituent of herbal medicines. The nucleotide complement of such an extract was purified and compounds identified by chromatographic behaviour, UV absorbance/pH profile, base‐to‐phosphate ratio, acid hydrolysis, and by fast‐atom bombardment mass spectrometry with mass‐analysed ion kinetic energy spectrum scanning. In addition to eighteen common nucleotides, and two cyclic nucleotides, fifteen novel nucleotides were identified, comprising eight deoxynucleotides and two cyclic deoxynucleotides, ten aminoacylnucleotides and two nucleoside trisphosphates together with 2′‐phosphoadenosine‐3′,5′‐cyclic pyrophosphate, 5′‐phosphoadenosine‐2′,3′‐cyclic monophosphate and N6,N6‐dimethyladenosine‐5′‐monophosphate. The possible origin and potential actions of these novel compouds are discussed.
Study of the interactions of intense laser beams and of fast‐ion beams with molecules
Authors: Kumar G. Ravindra , Safvan C. P. , Rajgara F. A. , Mathur D.
Published: May 2005

Molecular dynamics in intense, pulsed laser fields is an emerging frontier of research in laser–matter interactions. Mass spectrometric techniques are essential to understanding the behaviour of molecules in such fields. We present some salient features of this activity and review some of our recent experimental observations. Results concerning the roles of dissociation and ionization of simple diatomics and triatomics are presented. Further, comparisons are made between the forces experienced by molecules in intense laser fields and in collisions with fast ion projectiles. The dissociative ionization patterns of CS2 and CH4 in the two situations are discussed and the differences in the intense laser field dissociative ionization are attributed to the polarization property of laser light.
Application of the time‐dependent wavepacket method to mass spectrometric studies of molecular excitation and dissociation
Authors: Krishnamurthy M. , Gross P. , Mathur D.
Published: May 2005

A new time‐dependent wavepacket approach has been applied to illustrate a rigorous method of calculating the transition function for bound‐to‐continuum transitions in translational energy spectrometric experiments. The method is numerically exact and fully quantal, and is devoid of any classical or semi‐classical approximations. The validity of the hitherto‐applied reflection approximation is investigated in a comparative study. The method has been applied to two different translational energy spectrometry experiments: collision‐induced dissociation of CO+ and collisional excitation of H2.
Light emission from impacts of energetic proteins on surfaces and a light emission detector for mass spectrometry
Authors: Sullivan Patrick A. , Axelsson Jan , Sundqvist Bo U. R.
Published: May 2005

Photon emission from impacts of electrosprayed protein ions onto Au, Ta, Si and CsI surfaces was studied. Mass spectra of insulin, lysozyme and apo‐myoglobin were acquired by scanning the mass‐to‐charge ratio of a quadrupole mass filter while simultaneously detecting the photon and secondary electron signals. These spectra were very similar, but spectra acquired using photons displayed a somewhat better signal‐to‐noise ratio. The estimated photon emission yield is of the order of 0.5 photons per ion impact, a quantity which is not strongly dependent on target material. A higher yield of photons per incident ion was observed for apo‐myoglobin and lysozyme ions than for insulin ions.
Mass spectral fragmentation patterns of some new 3,7‐dichloro‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐dicarboxylic acid dianilides and 3,5‐dichloro‐dithieno[3,2‐b:2′,3′‐d]thiophene‐2,6‐dicarboxylic acid dianilides. II
Authors: Karminski‐Zamola Grace , Malešević Miro , Blažević Nikola , Bajić Miro , Boykin David W.
Published: May 2005

The electron impact mass spectra of some benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐dicarboxylic acid dianilides and dithieno[3,2‐b:2′,3′‐d]thiophene‐2,6‐dicarboxylk acid dianilides are discussed. Dominant peaks in these dianilides are formed by the cleavage of a CN bond on one side of an anilino group. These ions fragment further by the cleavage of a CC bond on the other side of an anilino group and a CONRPhR′ group may be lost directly. After loss of CO, the characteristic benzodithiophene radical cation, C10H2S2Cl, at m/z 256 and the dithienothiophene radical cation, C8S3Cl, at m/z 262 are formed from their respective precursor compounds.
Fragmentation rules in plasma desorption mass spectrometry
Authors: Kargar Taraneh , Bourcier S. , Hoppilliard Y.
Published: May 2005

Several studies concerning the analysis and quantification of biological and pharmaceutical compounds have been effected during the past 20–30 years using different techniques of desorption‐ionization. In most cases, however, the authors have not been interested in the mass spectrometric fragmentation mechanisms of these products. Plasma desorption mass spectrometry (PDMS) is a powerful technique for analysing, without matrix interferences, solid biological and pharmaceutical compounds. In this work, we use PDMS in order to study the influence of the amine (amide) function on the fragmentation processes of nitrogen‐containing compounds. For this work, quaternary ammonium salts, trisubstituted amines, disubstituted amines and a compound with an amide function were chosen. Classical PD mass spectra, accurate mass measurements, transitions in the field free region (FFR), labelled compound spectra and thermodynamical data are reported for the structural study of these compounds. Our results allow us to propose fragmentation rules for positively charged nonfunctional biological nitrogen compounds. These rules relate to a class of structurally informative decomposition reactions that can be applied to the determination and of identification of structural unknowns.
Translational energy spectroscopy. Spin‐conservation studies in collisional excitation processes
Authors: Enos C. S. , Lee A. R. , Brenton A. G.
Published: May 2005

High‐resolution translational energy spectroscopy is an effective means of obtaining detailed state‐selective information, permitting systematic investigation of spin conservation in collisional processes. In this paper, we examine collisional excitation of one selected singlet (N2) and one non‐singlet (O2) target by a variety of projectile ions, providing a kaleidoscope of assorted effects.
Characterization of polymers by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry: Molecular weight estimates in samples of varying polydispersity
Authors: Montaudo Giorgio , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo
Published: May 2005

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) allows the detection of large molecules such as those present in synthetic and natural macromolecules. Synthetic polymers may show a wide range of molecular weight distributions (MWD), according to the synthetic method used in their preparation. We have studied several poly(methylmethacrylate) (PMMA), poly(styrene) (PS) and poly(ethyleneglycol) (PEG) samples with varying MWD, and also a number of condensation polymers such as Nylon‐6, poly(carbonate) and poly(ester). Measurements of MALDI‐TOF spectra in the linear mode were used in our work to estimate the molecular weight (MW) and MWD of the polymer samples. Our results show that the molecular weight estimates provided by MALDI‐TOF measurements agree with the values obtained by conventional techniques, such as gel‐permeation chromatography (GPC), only in the case of polymer samples with very narrow molecular weight distribution. However, when the polydispersity reaches values around 1.10 the difference between the MW measured by GPC and measured by MALDI may amount to up to about 20%. At higher dispersions, the MALDI spectra fail to yield reliable MW values.
1995 directory of mass spectrometry manufacturers and suppliers
Authors: Lammert Stephen A.
Published: May 2005

An annual directory of companies that supply mass spectrometers and mass spectrometry components and services.
Negative electrospray ionization mass spectrometry analysis of gangliosides, sulphatides and cholesterol 3‐sulphate
Authors: Ghardashkhani S. , Gustavsson M. L. , Breimer M. E. , Larson G. , Samuelsson B. E.
Published: May 2005

Negative electrospray ionization mass spectrometry (NESI‐MS) of a series of native gangliosides containing one, two or three sialic acid groups, sulphatide‐I and cholesterol 3‐sulphate was undertaken, using a magnetic sector instrument. The results show that NESI‐MS of gangliosides leads to the formation of multiple‐charged molecular ions of the type [M  H]−, [M  2H]2− and [M  3H]3−. The number of charges appears to be correlated to the number of sialic acid groups present. NESI‐MS of sulphatide‐I predominantly gave ions of type [M  H]− whilst cholesterol 3‐sulphate gave a more complex ionization pattern. The sensitivity of the NESI‐MS system was enhanced by using water+methanol, 9:1 (v/v) as solvent, containing 300 pmol/μL of NH4HCO3. The application of NESI‐MS to these compounds is discussed.
Fumonisin B1 analysis with capillary electrophoresis–electrospray ionization mass spectrometry
Authors: Hines Harry B , Brueggemann Ernst E. , Holcomb Manuel , Holder Claude L.
Published: May 2005

Fumonisin B1, a mycotoxin produced by a common fungal contaminant of corn, Fusarium moniliforme, was analyzed by capillary electrophoresis–electrospray ionization mass spectrometry. System performance was maximal with uncoated columns. System efficiencies of approximately 44 000 plates/m and reproducible analysis times of about 13 min were obtained. System efficiency with methyl‐coated columns was approximately 24 000 plates/m. Reproducible analysis times of about 3.5 min were obtained with these columns. With uncoated columns, the concentration limit of detection was 156 ppb with a s/n ratio of approximately 10. The estimated injected mass at 156 ppb was 1.1 pg. Repeated injections of extracts containing constant fumonisin B1 concentrations showed that peak areas were slightly inconsistent, although generally similar to variations encountered with liquid chromatography‐electrospray ionization mass spectrometry. The source of this inconsistency was traced to sample solubility, errors inherent in electrophoresis injections, and electrospray instability. Minimizing these problem areas will produce a technique with peak area reproducibilities comparable to liquid chromatography–electrospray ionization mass spectrometry, but with potentially greater resolving power.
A study of factors influencing the formation of singly charged oligomers and multiply charged monomers by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Zhong Feng , Zhao Shankai
Published: May 2005

The formation of singly charged oligomers and multiply charged monomers has been studied under different conditions with matrix‐assisted laser desorption/ionization and it has been found that the concentration of analyte in matrix solution, as well as the matrix and substrate used, are factors that influence this process. The concentration of analyte in the matrix solution has a strong influence on the formation of singly charged oligomers. When α‐cyano‐4‐hydroxycinnamic acid is used as matrix, more doubly charged monomeric molecular ions are observed than when sinapinic acid is used. By using a nitrocellulose membrane instead of a silver plate as substrate, we find more multiply charged monomers and dimers in the spectra, especially in the case of high mass proteins, such as albumin. It seems that the formation of multiply charged monomers and oligomers is influenced by the overall amount of charge that the sample carries.
Isotope effects in the elimination of H and D atoms by dissociative charge transfer reactions in systems involving isotopic methanes
Authors: Ardelean Petru , Dunca Firuta , Cuna Cornel , Ioanoviciu Damaschin
Published: May 2005

The charge transfer reactions of H, CH, CH and N+ ions with CH4, CH3D, CH2D2 and CD4 were studied. The measurements were carried out using a tandem type mass spectrometer. The influence of the kinetic and internal energy of the incident ions was observed on the secondary mass spectra and also on the isotope effects expressed through πi(D/H), Ti(H) and Ti(D) factors. The dependence of the isotope effects on kinetic energy could indicate a conversion of kinetic energy into internal energy. Reactions in which momentum transfer resulted in charge transfer were also observed, probably indicating a ‘short‐range interaction’ reaction mechanism.
252Cf‐plasma desorption mass spectrometry analysis of lipids A obtained by an elimination reaction under mild conditions
Authors: Lebbar Souad , Karibian Doris , Haeffner‐Cavaillon Nicole , Beyec Yvon Le , Caroff Martine
Published: May 2005

Lipids A are the hydrophobic domains of bacterial endotoxic lipopolysaccharides. Since they are responsible for most of the biological activities (both pathogenic and beneficial) of endotoxins, the characterization of their structure is crucial to the understanding of their mode of action. However, the inadequacy of existing methods for preparing certain lipids A has prompted us to devise a new, mild procedure which gives intact products. Use was made of the special features of 252Cf‐plasma desorption mass spectrometry for forming molecular ions from these species and giving qualitative and quantitative information from the primary mass spectrum.
Fragmentation of a series of cyclic dipeptides in fast‐atom bombardment mass spectrometry
Authors: Henczi Maria , Weaver Donald F.
Published: May 2005

The positive‐ion mass spectra of a series of cyclic dipeptides have been obtained by fast‐atom bombardment mass spectrometry. The protonated molecules were mass selected and their collision‐induced dissociations were analysed by tandem mass spectrometry. This approach allowed an easy structural characterization of the above mentioned class of compounds for further pharmacological studies.
Chemical ionization and electron impact mass spectra of N‐carbonyldihydrazones of 2,4‐diacetylresorcinol
Authors: Kotali Antigoni
Published: May 2005

The methane chemical ionization mass spectra of N‐carbonyldihdrazones of 2,4‐diacetylresorcinol were recorded. The protonated molecular ion was found to be of variable abundance and was often accompanied by [M + 29]+ and [M + 41]+ ions. Electron impact mass spectra displayed weak molecular ions and were characterized by the scission of a NN bond and subsequent loss of XCONH and XCONHNH2.
Mass spectrometric study on two compounds from Skimmia caureola ssp. multinervia
Authors: He Meiyu , Zhang Hongjie , And Xiaoran He , Zhang Mingzhe
Published: May 2005

The mechanisms of the mass spectrometric fragmentation of two compounds, I (evoxine) and a new compound II (O‐methylcaureolol), were analyzed using mass‐analyzed ion kinetic energy spectrometry, and by verifying the elemental composition and structure of some important fragment ions by high‐resolution data. We discovered that the double bond in position 9,11 of the C ring of II may be diverted to position 7,8 of the B ring and that a typical retro‐Diels–Alder reaction follows.