bluuebunny/crossref_metadata_2025_split huggingface dataset:
Matrix‐assisted laser desorption/ionization of restriction enzyme‐digested DNA
Authors: Tang K. , Allman S. L. , Chen C. H. , Cháng L. Y. , Schell M. 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization, by a time‐of‐flight mass spectrometer, has been successfully used for detection of restriction enzyme‐digested DNA. However, the oligonucleotide segments detected correspond to the molecular weights of single strands.
Study of anticancer drug interaction with DNA by means of particle‐induced desorption mass spectrometry: Prospydine and deoxyguanosine‐5′‐monophosphate
Authors: Sukhodub Leonid F. , Grebenik Lujdmila I. , Chivanov Vadim D. 
Published: May 2005

AbstractUsing 252CF particle desorption mass spectrometry, the interaction between an antitumour drug prospydine (Pro) and deoxyguanosine‐5′‐monophosphate (pdG) has been studied. The adduct which corresponds to a peak at m/z 524.5 and which occurs as a result of the particular degradation of Pro during its alkalating of pdG has been found.
A method to increase contaminant tolerance in protein matrix‐assisted laser desorption/ionization by the fabrication of thin protein‐doped polycrystalline films
Authors: Xiang Fan , Beavis Ronald C. , Ens Werner 
Published: May 2005

AbstractThis paper describes the fabrication and use of thin polycrystalline films in matrix‐assisted laser desorption experiments. These films consist of microcrystals of protein‐doped matrix (crystal dimensions ⩽ 1 μm). The films produce intense protein‐ion currents and can be grown in the presence of high concentrations of involatile solvents (e.g., glycerol, 6 M urea) without any purification. They strongly adhere to the substrate, allowing easier washing of the film, compared to dried‐droplet deposits. The films are also more uniform than dried‐droplet deposits, with respect to ion production. It is suggested that matrix‐assisted laser desorption/ionization samples are composed of nonlinear optical devices that function as polymer ion‐current sources. These devices (protein‐doped matrix crystals) can be designed and fabricated in many forms to serve the special functions required by the analytical scientist.
Matrix‐assisted laser desorption/ionization with an external ion source Fourier‐transform mass spectrometer
Authors: McIver Robert T. , Li Yunzhi , Hunter Richard L. , Cotter Robert J. 
Published: May 2005

AbstractMass spectra of several model oligopeptides (substance P, [Arg8]‐vasopressin, tyrothricin, and the B‐chain of bovine insulin) have been obtained with a matrix‐assisted laser desorption/ionization (MALDI) source and a custom‐designed Fourier‐transform mass spectrometer (FTMS). The MALDI source is outside the magnetic field in a separately pumped external chamber, and ions are injected through the fringing fields of the magnet and into the FTMS analyzer cell by a long quadrupole mass filter that is operated in the RF‐only mode. A large window on the ion source housing makes it easy to point and focus the laser beam onto the sample probe tip. A good quality mass spectum is achieved for 0.5 pmol of substance P, and the mass resolution for the B‐chain of bovine insulin is 19000.
Single‐electron capture spectra for Ar3+ in argon and xenon
Authors: Lee Anthony R. , Wilkins Adam C. R. , Enos Christopher S. , Gareth Brenton A. 
Published: May 2005

AbstractHigh‐resolution translational energy spectra have been obtained for Ar2+ ions resulting from single‐electron capture by 9 keV Ar3+ ions in argon and xenon gas targets. Our result for Ar3+ in argon is broadly in agreement with previous high‐resolution studies, but we have further successfully assigned reaction channels to three peaks which were previously observed but not definitively identified. These channels appear to involve capture of a 3s‐electron from the target argon atom to form Ar+ ions in the first excited state Ar+[3s3p6 2S]. The capture spectrum for Ar3+ in xenon displays eleven relatively well defined peaks with exothermic energy changes in the range of 4–12 eV. However, these capture channels are difficult to identify with certainty because they involve capture into closely spaced high excited states of Ar2+, and are further complicated by the splitting (1.31 eV) of the ground‐state doublet 2P target Xe+ product ion. There are over one hundred competing channels, comprising three entrance and over forty exit channels, within this range of energy change. Tentative assignments of capture channels have been made, guided by electron‐core configuration and spin‐conservation requirements.
Gas chromatography/combustion/isotope‐ratio mass spectrometry analysis of urinary steroids to detect misuse of testosterone in sport
Authors: Becchi Michel , Aguilera Rodrigue , Farizon Yves , Flament Marie‐Magdeleine , Casabianca Hervé , James Patrick 
Published: May 2005

AbstractWe propose a new confirmatory method for testosterone doping in sport. The present method in use, based on measuring the testosterone/epitestosterone (T/E) ratio in urine, may miss suspicious cases, or lead to reporting cases in which the high ratio is natural. Synthetic testosterone has a 13C abundance different from that of endogenous human testosterone. The connection of a gas chromatograph to an isotope‐ratio mass spectrometer via a combustion interface allows the measurement of the corresponding characteristic value (δ‰) for testosterone, its precursors, and its metabolites. To detect exogenous administration of testosterone, 30–40 mL of urine is sufficient.
Cycloaddition reactions between 1,3‐butadiene radical cations and ethene in the gas phase
Authors: Bouchoux Guy , Salpin Jean‐Yves , Turecek Frantisek 
Published: May 2005

AbstractThe reaction of [1,3‐butadiene]+· with ethenc in the gas phase has been studied under low‐pressure conditions. Experiments were conducted in a Fourier transform ion cyclotron resonance spectrometer equipped with an external ion source. Two competitive reaction paths were identified: [CH2CHCHCH2]+·+CH2CH2→ [C5H7]++CH3· (Reaction I) and [CH2CHCHCH2]+·+CH2CH2→[C4H6]+·+C2H4 (Reaction II). Deuterium labelling reveals that the methyl loss (Reaction I) is preceded by extensive H/D scrambling inside the transient collision complex and that the ethene molecule eliminated during Reaction II contains specifically one methylene group from the terminal positions of the 1,3‐butadiene radical cation and the other from the initial neutral ethene used as reactant. Measurements of deprotonation enthalpies indicate that the [C5H7]+ ions produced via Channel I have the cyclopentadienyl structure. A reaction mechanism, corroborated by molecular orbital calculations (3‐21G), is proposed. It involves the initial formation of a distonic species [CH2CHCHCH2CH2CH2]+· as a key step and competitive processes such as [1 + 2] cycloadditon, 1,n‐hydrogen transfers and nonsynchronous Diels‐Alder cycloaddition.
Improved detection of glucuronide and glutathione conjugates with thermospray ionization following esterification
Authors: Haroldsen Peter E. , Baillie Thomas A. 
Published: May 2005

AbstractAnalysis by thermospray of glucuronide and glutathione conjugates as the corresponding methyl‐, propyl‐, or hexyl esters is demonstrated to yield a remarkable increase in positive pseudomolecular ion production and to result in a dramatic improvement in detectability of these thermally labile compounds as intact molecular structures. In the most extreme examples a 450‐fold increase in the [M + NH4]+ ion intensity was observed for mycophenolic acid glucuronide bis‐propyl esters vs. the native conjugate and an 860‐fold increase in the [M + H]+ ion intensity was achieved for acetaminophen glutathione bis‐hexyl ester vs. the native conjugate. Following esterification, seventeen of the eighteen glucuronide esters analyzed demonstrated an increase in totalion‐current yield ranging from 1.1‐ to 8.3‐fold while eighteen of the twenty‐one glutathione esters examined demonstrated an increase in totalion‐current yield from 2.0‐ to 26.3‐fold. For both types of conjugates a trend in increased relative abundance of the positive pseudomolecular ion intensity is observed as the hydrophobicity of the ester increases from methyl to hexyl. For the glutathione conjugate esters, the [M + H]+ ion represented the base peak in the mass spectra of the majority of samples analyzed. This approach improves the protonated‐ or ammoniated‐molecular‐ion abundances of the conjugates to such an extent that it provides a means for unambiguous molecular weight assignments to be made. Although the exact mechanism(s) for the observed phenomenon is not known, it appears that the improvement in sensitivity for the conjugate esters over the corresponding native conjugates involves an increase in pseudomolecular‐ion stability and also in part an increased ionization efficiency of the esterified molecule.
Laser mass spectrometry of the Di‐, Tri‐ and tetrachlorobenzenes: Isomer‐selective ionization and detection
Authors: Weickhardt Christian , Zimmermann Ralf , Schramm Karl W. , Boesl Ulrich , Schlag Eduard W. , Lubman D. M. 
Published: May 2005

AbstractThe resonant two‐photon ionization spectra of the S1←S0transition of all di‐, tri‐ and tetrachlorinated benzene isomers, cooled by supersonic jet expansion, are presented. As the spectra are well structured and isomer specific, this technique allows selective ionization of a single isomer out of mixtures such as, for example, environmental samples. Reflectron time‐of‐flight mass spectrometry is used for the mass‐selective detection of the ions.
Ion fragmentation activated by matrix‐assisted laser desorption/ionization in an ion‐trap/reflectron time‐of‐flight device
Authors: Fountain Scott T. , Lee Heewon , Lubman David M. , Brodbelt Jennifer 
Published: May 2005

AbstractAn ion‐trap storage/reflectron time‐of‐flight mass spectrometer has been used to study the decay of large ions following activation by matrix‐assisted laser desorption/ionization (MALDI). It is shown that large ions may undergo fragmentation over long periods of time, extending even to milliseconds in some cases. These fragments are stored in the trap and detected as stable ions in the reflectron device, rather than as metastable ions due to decay during the flight time to the detector. The ion decay is found to depend strongly on the laser intensity, while a smaller effect may be due to the matrix used in the MALDI process. The fragmentation observed was found to also depend strongly on the RF voltage applied to the ring electrode; higher RF voltage produced enhanced fragmentation. A gated RF experiment further demonstrated the importance of the level of the RF voltage, during the initial activation event, in producing fragmentation. A study of the effects of buffer gas composition and pressure showed that increased pressure may result in reduced fragmentation due to collisional cooling in the trap. However, the use of argon or nitrogen buffer gas at increased pressure in the trap may result in fragmentation upon extraction from the trap, producing metastable ions in the flight tube. The implications of the use of the time variable for obtaining fragmentation in the trap for rapid sequencing are discussed.
Fragmentation of vinyl triflates by electron impact. Mechanism of an unusual double hydrogen atom transfer reaction
Authors: Martínez Antonio García , Fernández Antonio Herrera , Alvarez Roberto Martínez , Barcina José Osío , Vilar Enrique Teso , Fraile Amelia García , Subramanian Lakshminarayanapuram R. , Märkl Reiner , Hanack Michael 
Published: May 2005

AbstractThe main fragmentation pathway of vinyl triflates in mass spectra involves the loss of CF3SO, followed by the loss of olefin and/or CO. The loss of TfOH takes place with fragmentation of a vinylic CH bond. TfOH ions are formed via regiospecific double hydrogen transfer from five‐ and six‐membered cyclic triflates.
Mass spectrometry in isomer differentiation: 4,5‐bis(alkylthio)‐1,3‐dithiol‐2‐ones and 1,2‐dithiol‐3‐ones
Authors: Andreu Raquel , Gayán Isabel , Garín Javier , Orduna Jesús , Savirón María 
Published: May 2005

AbstractDifferences in the electron ionization mass spectra of 4,5‐bis(alkylthio)‐1,3‐dithiol‐2‐ones and 4,5‐bis(alkylthio)‐1,2‐dithiol‐3‐ones have been studied by metastable analysis and collision‐induced dissociation. Analogies in the spectra are due to the presence of common [M—CO]+· ions rather than to isomerization of molecular ions.
Reverse‐phase liquid chromatography/electrospray‐ionization Fourier‐transform mass spectrometry in the analysis of peptides
Authors: Stacey Catherine C. , Kruppa Gary H. , Watson Clifford H. , Wronka John , Laukien Frank H. , Fred Banks J. , Whitehouse Craig M. , Voyksner Robert D. 
Published: May 2005

AbstractElectrospray ionization (ESI) in combination with Fourier‐transform mass spectrometry (FTMS) gives both highly accurate mass analysis of peptides with external calibration and high resolution for charge‐state determination of an ion from the naturally occurring isotopic peaks. Liquid chromatographic (LC) separation of peptides is important for the analysis of complex mixtures. High‐resolution, high accuracy measurement of the molecular ions of the mix of peptides has been achieved with LC/ESI‐FTMS. Examples are given to show both the reproducibility of mass accuracy over replicate analyses and to show the utility of broadband analysis of a gradient separation of peptides. The high mass accuracy and resolution of FTMS was uncompromised for the direct analysis of chromatography peaks.
Detection and identification of explosives compounds using laser ionization time‐of‐flight techniques
Authors: Marshall Archibald , Clark Alastair , Ledingham Kenneth W. D. , Sander Joseph , Singhal Ravi P. , Kosmidis Constantinos , Deas Robert M. 
Published: May 2005

AbstractResonance‐enhanced multiphoton ionization has been used to detect the presence of vapour‐phase explosive‐type samples in a linear time‐of‐flight (TOF) mass spectrometer. In particular, nitrobenzene, 2‐nitrotoluene, 2,4‐dinitrotoluene, 2,4,6‐trinitrotoluene, ethylene glycol dinitrate, pentaerythritol tetranitrate (PETN), 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX) and SEMTEX (PETN plus RDX plus plasticizer) have been analysed at a laser wavelength of 226.3 nm corresponding to a strong resonant transition of the neutral NO molecule. TOF mass spectra have been recorded and the intensity of the NO+ ion monitored as a function of temperature for comparison with the temperature dependence of the various vapour pressures.
Electron ionization mass spectra of some fused pyrimidinone derivatives
Authors: Mäki Esa , Fülöp Ference , Bernáth Gabor , Pihlaja Kalevi 
Published: May 2005

AbstractThe electron ionization mass spectra of 19 tricyclic fused pyrimidinone derivatives were studied. The molecular ions of almost all of these compounds were very stable and formed the base peaks of the spectra. The degree of saturation, the size and substitution of rings A and C (pyrimidinone itself is ring B) were the dominant factors affecting the type of fragmentation which, however, in general was quite simple.
Determination of the amino acid sequence of apamin by tandem mass spectrometry
Authors: Lange C. , Marvin L. , Marcual A. , Ordsmith N. , Bordoli R. S. 
Published: May 2005

AbstractA new strategy has been developed for the determination of the amino acid sequence of apamin, a two disulfide‐bond neurotoxic oligopeptide. Relative molecular mass up to about 2000 was determined using electrospray mass spectrometry. This technique shows that three basic amino acid residues are present in apamin. A hydrophobic tryptic digest fragment was sequenced using fast‐atom bombardment combined with tandem mass spectrometry. But the full sequence has been directly observed using a tandem mass spectrometer: the daughter‐ion mass spectrum of protonated molecules of dithiothreitol‐reduced apamin gives the sequence.
Development of packed capillary column electrochromatography/mass spectrometry
Authors: Gordon Derek B. , Lord Gwyn A. , Jones David S. , Games David E. 
Published: May 2005

AbstractThe enhanced performance of electro‐osmotically driven high performance liquid chromatography (HPLC) using reversed‐phase packed capillaries has been evaluated for coupling to mass spectrometers, as an alternative to both conventional pressure‐driven elution, and to micellar electrokinetic capillary chromatography for the separation of neutral analytes. An off‐line comparison of electro‐osmotically driven versus pressure driven chromatography for the separation of an aromatic mixture shows the superiority of the method over conventional HPLC. Coupling of the technique with continuous‐flow fast‐atom bombardment for the analysis of a steroid mixture is described.
Analysis of mass‐analyzed ion kinetic energy peak profiles. III. Analytical expression for a peak shape generated by collisionally activated dissociation
Authors: Lee Young Jin , So Hun Young , Kim Myung Soo 
Published: May 2005

AbstractAn analytical expression has been derived for the mass‐analyzed ion kinetic energy spectral profile of a daughter ion produced by collisionally activated dissociation. Effects of the Y and Z instrumental discriminations on the peak shape have been accounted for. The peak shift due to Y deflection by collision has also been taken into account. Peak profiles calculated by the present method have been found to be in excellent agreement with those calculated by the rigorous ion‐optical trajectory method. A drastic reduction in computing time, by four orders of magnitude, is the main advantage of the present method.
Determination of acid sites in solid catalysts by mass spectrometry
Authors: Aramendí María Angeles , Borau Victoriano , Jiménez Cesar , Marinas José María , Porras Andrés , Urbano Francisco José 
Published: May 2005

AbstractThis paper reports a temperature‐programmed desorption mass spectrometry method for determining the nature, number and distribution, according to relative strength, of acid sites in solid catalysts. By using pyridine as the titrant, the overall, Brönsted (B) and Lewis (L) acidities are determined. The Brönsted acidity is obtained individually by titration with 2,6‐dimethylpyridine, whereas the Lewis acidity is calculated by difference. The desorption temperatures for the amines are used as measures of the relative strengths of the different types of acid sites. The results obtained are compared with those provided by a UV‐visible spectrophotometric method reported elsewhere (J. M. Campelo et al., Can. J. Chem. Vol. 61, p. 544 (1983)).
Multiphoton ionization and dissociation of nitrotoluene isomers by UV laser light
Authors: Kosmidis Constantine , Marshall Archibald , Clark Alastair , Deas Robert M. , Ledingham Kenneth W. D. , Singhal Ravi P. , Harris Frank M. 
Published: May 2005

AbstractThe photofragmentation of the nitrotoluene isomers in the gas phase is studied in the wavelength region 210–270 nm using a pulsed UV laser in conjunction with a time‐of‐flight mass spectrometer. Laser‐induced mass spectra are analysed and compared with those produced by the electron impact technique. The generation of the observed fragment ions is explained by invoking different fragmentation pathways followed by these molecules. Observed differences in the mass spectra of the ortho‐ meta‐, and para‐nitrotoluene isomers and in the wavelength dependence of the NO fragment released from these molecules are discussed as a possible way of providing a laser‐based method for their identification.
Wide‐mass‐range axialization for high‐resolution Fourier‐transform ion cyclotron resonance mass spectrometry of externally generated ions
Authors: Marto Jarrod A. , Guan Shenheng , Marshall Alan G. , Buchanan Michelle V. 
Published: May 2005

AbstractIons generated in both continuous and pulsed‐mode external ion sources are injected into an open‐ended cylindrical Fourier‐transform ion cyclotron resonance ion trap by means of an electrostatic ion guide consisting of concentric cylinder and wire electrodes to which a potential difference is applied. Broadband axialization during ion injection improves ion trapping efficiency by reducing the ion off‐axis displacement. Significant improvements in both signal‐to‐noise ratio and mass resolving power, along with high mass selectivity are demonstrated for ions generated by external Cs+secondary ion mass spectrometry or by matrix‐assisted laser desorption/ionization.
Mass spectrometry in stereoisomer characterization: The case of 1,3,4‐trideoxy‐3‐fluoronojirimycins and 1,3,4‐trideoxy‐3‐fluoromannojirimycins
Authors: Favretto Donata , Catinella Silvia , Traldi Pietro , Resnati Giuseppe 
Published: May 2005

AbstractThe mass spectrometric characterization of stereoisomeric 1,3,4‐trideoxy‐3‐fluoronojirimycins and 1,3,4‐trideoxy‐3‐fluoromannojirimycins has been achieved by means of metastable ion studies. In particular, mass‐analyzed ion kinetic energy spectroscopy performed on the electron‐ionization‐generated molecular species of the title compounds has led to an easy and unequivocal differentiation of the four stereoisomers under study, by their unusual diagnostic fragmentation mechanisms.
Secondary‐ion mass spectrometry methodology and surface chemistry of mixed oxide electrodes: Modifications induced by noble‐metal content
Authors: Daolio Sergio , Facchin Bruno , Pagura Cesare , De Battisti Achille , Barbieri Andrea 
Published: May 2005

AbstractMixed‐oxide coatings are extensively used in the electrochemical industry. Secondary‐ion mass spectrometric data confirm that technological research can indeed find a new way of controlling precursors, synthesis conditions, purity of coatings and electrodic activity. Results obtained by argon and oxygen primary‐ion bombardment of RuO2/TiO2, IrO2/TiO2, RuO2/IrO2/TiO2 films are reported. The presence of metal, metal oxide and cluster ions suggests a more systematic use of secondary‐ion mass spectrometry in the elucidation of catalytic aspects. In‐depth profiles of some ionic species and their correlation with parameters that induce significant modifications can help in the understanding of the solid state physics and inorganic chemistry involved.
Picolinic acid as a matrix for laser mass spectrometry of nucleic acids and proteins
Authors: Tang K. , Taranenko N. I. , Allman S. L. , Chen C. H. , Chág L. Y. , Jacobson K. B. 
Published: May 2005

AbstractWe found that picolinic acid is a very good matrix for matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometry of oligonucleotides, proteins and tRNA. Among the oligonucleotides, picolinic acid was shown to be effective for homo‐oligonucleotides, d(G)40 and d(C)60, and for mixed‐base oligonucleotides up to 190 bases. In the case of the single‐stranded oligonucleotides, and of double‐stranded ones as well, only parent ions corresponding to single‐stranded DNA were observed. The efficiency for MALDI of oligonucleotides using the picolinic acid matrix was superior to that using 3‐hydroxypicolinic acid. MALDI of transfer RNA phenylalanine‐specific (tRNAphe), a 76‐base ribonucleic acid, was detected with a signal‐to‐noise ratio of >10. By comparison with 3‐hydroxypicolinic acid the results with picolinic acid are notably superior for all oligonucleotides.
Matrix‐assisted laser desorption/ionization mass sectrometry of restriction enzyme‐digested plasmid DNA using an active nafion substrate
Authors: Bai Jian , Liu Yan‐Hui , Lubman David M. , Siemieniak David , Chen Chung‐Hsuan 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization using a 3‐hydroxpicollinic acid matrix from an active Nafion substrate has been used for detection of restriction enzyme‐degested double‐stranded plasmid DNA using time‐of‐ flight mass spectrometry. DNA strands of up to 267 base pairs were detected with minimal sample purification, although only as species corresponding to single‐stranded DNA.