bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton‐transfer reactions of mass‐selected multiply charged ions
Authors: Hunter Ann P. , Severs Joanne C. , Harris Frank M. , Games David E. 
Published: May 2005

AbstractA triple‐quadrupole spectrometer has been used to study proton‐transfer reactions of multiply charged ions generated by electrospray ionization. Doubly and triply charged ions generated from the peptides Arg‐Lys‐Glu‐Val‐Tyr and Met‐Lys‐bradykinin, respectively, were found to undergo proton‐transfer reactions with ammonia molecules contained in the RF‐only quadrupole collision‐gas cell of the spectrometer. With horse‐heart myoglobin in the source, ions having charges of 20+, 19+, 16+ and 14+ were selected in turn by the first quadrupole and their proton‐transfer reactions with ammonia investigated. For each ion, numerous product ions were detected having charges (n‐1)+, (n‐2)+, (n‐3)+ … where n was the charge on the reacting parent ion. The possibility of using the experimental technique to measure approximately the proton affinities of multiply charged ions is discussed. Also, a procedure is outlined for identifying the charge states of product ions resulting from collision‐induced dissociation of multiply charged ions.
Interconversion of chemical species during analysis by gas chromatography/mass spectrometry
Authors: Monaghan John J. , Wagner Martin H. 
Published: May 2005

AbstractThe electron ionization mass spectra obtained, on two types of GC/MS instrument, of an impurity peak in a sample of fluorotrichloroethene (1) were those of two different compounds, viz., the epoxide of 1 and trichloroacetyl fluoride. Confirmation of the latter structure was provided by evidence from infrared spectroscopy. A study, on both instruments, of the variation of injector, source and interface temperatures has shown that the sample impurity is actually the epoxide which, at sufficiently high interface‐region temperatures, can be converted to the acyl fluoride species. Ab initio molecular orbital calculations have confirmed that the acyl fluoride is more stable than the epoxide.
Different mass spectrometric approaches in the identification of endogenous methylated purine bases in urine extracts
Authors: Porcelli Brunetta , Pagani Roberto , Lorenzini Luciano , De Martino Antonio , Catinella Silvia , Traldi Pietro 
Published: May 2005

AbstractA preliminary identification of endogenous and exogenous methylated purine bases in urinary extracts of healthy and tumor‐bearing subjects has been performed using high performance liquid chromatography, and tandem mass spectrometry (MS/MS). MS/MS gave particularly fast and sensitive analyses, allowing the simultaneous and rapid determination of 26 different urinary methylated purines. Both sets of data confirm that tumor‐bearing patients show changed levels of methylated purine bases.
Tryptic peptide mapping of sequence 1–298 of human serum albumin by high‐performance liquid chromatography and fast‐atom bombardment mass spectrometry
Authors: Compagnini Anna , Fisichella Salvatore , Foti Salvatore , Saletti Rosaria , Sardo Letizia 
Published: May 2005

AbstractThe determination of the tryptic peptide mapping of sequence 1–298 of human serum albumin (HSA) by chemical and enzymatic cleavage and combined use of high‐performance liquid chromatography (HPLC) and fast‐atom bombardment mass spectrometry (FAB‐MS) is described. A total coverage of about 75% of the entire sequence was obtained. Unidentified fragments included some peptides which were not present in the chromatograms because of their extreme hydrophobic or hydrophilic character, as indicated by the calculated retention times. Due to the high reproducibility of the experiments and to the satisfactory yield of the tryptic fragments identified, the combined use of HPLC and FAB‐MS appears to possess great potential for structural investigation of HSA.
Carbon dioxide laser desorption/ionization mass spectrometry of a mixture of s‐triazine oligomers analyzed by a method which assumes a pattern of chemical formulae
Authors: Togashi Hisashi , Koga Yoshinori , Kakudate Yozo , Fujiwara Shuzo , Kubota Masaaki , Fukuda Kenzo , Nakagawa Hideki , Kawaguchi Masayuki 
Published: May 2005

AbstractMass spectra of intermediate products of polymer [(C3N3)2(NH)3]n were obtained by carbon dioxide laser desorption/ionization Fourier‐transform mass spectrometry and analyzed by a method which assumes the presence of a pattern of chemical formulae. It was found that a group of chemical formulae CxNyHz+ (4x‐3y+z=1) applies to most of the observed ions. These formulae were found to correspond to the ionic structures which are expected from a knowledge of reactions of s‐triazine derivatives.
The gas‐phase baker venkataraman rearrangement
Authors: Dua Suresh , Amemiya Sadaka , Bowie John H. 
Published: May 2005

AbstractThe condensed‐phase Baker Venkataraman rearrangement is an irreversible reaction, e.g. o‐(−CH2CO)C6H4OCOPh → o‐(−O)C6H4COCH2COPh. The collision‐induced mass spectra of these two ions show the corresponding gas‐phase reaction to be reversible.
Direct analysis of samples on paper by fast‐atom bombardment mass spectrometry
Authors: Zhongping Yao , Hanhui Wen , Qinming Zha , Weide He , Shankai Zhao 
Published: May 2005

AbstractA method for obtaining fast‐atom bombardment mass spectra of samples on paper is described in which a scrap trimmed from the paper of interest is adhered to the FAB probe tip with a strip of double‐faced adhesive tape. After addition of suitable matrix (e.g. glycerol or thioglycerol) to the scrap, the probe is introduced into the mass spectrometer to obtain mass spectra in the usual manner. The method is demonstrated by analysing some paper containing hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate and vanillic acid. The method is also used to characterize paper chromatographic spots, by which the fractions of a mixture of three amino acids (L‐glutamic acid, L‐proline and L‐valine) separated by paper chromatography are easily determined. The detection limit of the method is well below 10 ng with respect to hexadecyltrimethylammonium bromide.
Collision‐induced dissociation mass spectrometry of the herbicide diclofop‐methyl
Authors: Headley John V. , Peru K. M. , Brooks Paul W. 
Published: May 2005

AbstractThe collision‐induced dissociation (CID) spectra of positive ions of the herbicide diclofop‐methyl are reported. The results indicate that for relatively low collision energies (⩽75eV, laboratory frame of reference), the distribution of the CID ions of the molecular ion correlates in a qualitative manner with the occurrence of transformation products arising from the degradation of the herbicide in geologic or biofilm materials. At low collision energies (30‐45 eV, laboratory frame of reference), the CID spectra contained a preponderance of product ions at m/z 281 and 253. These product ions correspond to prevalent transformation products in soil, 4‐(2,4‐dichlorophenoxy)dehydrophenetole (molecular ion 282) and 4‐(2,4‐dichlorophenoxy)phenol (molecular ion 254) respectively. At higher collision energies (⩾45eV), product ions were observed for up to three bond cleavages. The high energy CID product ions correspond to transformation products observed in mature biofilm materials cultivated on the parent herbicide as the sole carbon source.
Detection of nucleotide bases in ancient seeds using gas chromatography/mass spectrometry and gas chromatography/mass spectrometry/mass spectrometry
Authors: O'Donoghue Kerry , Brown Terence A. , Carter James F. , Evershed Richard P. 
Published: May 2005

AbstractNucleic acid extracts from 1400‐year‐old radish seeds recovered from excavations at Qasr Ibrim, Upper Egypt, have been analysed by gas chromatography/mass spectrometry and gas chromatography/mass spectrometry/mass spectrometry. tert‐Butyldimethyisilyl derivatives of the purine and pyrimidine bases were prepared, after treatment of the nucleic acid extracts with concentrated formic acid. Under electron ionization these derivatives yield prominent [M–57]+ ions that were found to be of value for use in analyses employing selected‐ion monitoring and product‐ion studies. These two techniques were used in the sensitive and selective detection of nucieotide bases in crude extracts of ancient seeds. The results obtained were supported by complementary analyses of hydrolysates of ancient nucleic acids and authentic bases by means of retention time and spectral comparisons. This work demonstrates for the first time that mass spectrometry can be used in the direct chemical examination of nucleotide bases in ancient materials. This analytical approach is currently being used to address questions regarding the possible chemical (diagenetic) changes occurring in the nucleic acids of ancient biological material.
The methyleneketene radical anion
Authors: Dua Suresh , Sheldon John C. , Bowie John H. 
Published: May 2005

AbstractThe methyleneketene radical anion is formed from Me3SiCOCHCH2. Deprotonation of this neutral by NH yields Me3SiCOC̄CH2 which then decomposes by loss of Me3Si· to yield CH2CCO−·. The identity of the product radical anion is determined by its charge‐reversal (positive ion) mass spectrum.
Effect of multiple sprayers on dynamic range and flow rate limitations in electrospray and ionspray mass spectrometry
Authors: Kostiainen Risto , Bruins Andries P. 
Published: May 2005

AbstractThe sample‐ion signal in electrospray mass spectrometry is an approximately linear function of sample concentration up to 10−5mol/L. Dynamic range for the tetrabutylammonium ion signal and spray current leaving the nebulizer are determined with one and two sprayers, at flow rates of 5 and 10 μL/min, and at different positions of the sprayer. The dynamic range does not appear to be limited by the total amount (mass) of sample, but by the concentration of the sample solution introduced into the ion source, as is demonstrated by the use of two parallel sprayers. Limitation of dynamic range as a result of increasing repulsion between charged droplets at higher sample concentration appears to be unlikely. The efficiency of droplet charging gradually decreases with increasing sample concentration, while the detector signal abruptly reaches a plateau. Limitation just by insufficient charge on droplets is ruled out. Limitation of sample‐ion signals can be attributed to an upper limit to the number of free quaternary ammonium ions at the surface of electrically charged droplets.Multiple sprayers can be used to increase the range of flow rates accepted by the electrospray interface. In the case of ionspray (pneumatically assisted electrospray) the stability of the ion signal at higher flow rates is improved by the use of multiple sprayers.
Attomole detection of proteins by matrix‐assisted laser desorption/ionization mass spectrometry with the use of picolitre vials
Authors: Jespersen S. , Niessen W. M. A. , Tjaden U. R. , van der Greef J. , Litborn E. , Lindberg U. , Roeraade J. , Hillenkamp F. 
Published: May 2005

AbstractSignificant improvements in the absolute detection limits for proteins in matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) are demonstrated by the application of so‐called picolitre vials. By the reduction of the sample volume from a few μL down to 250 pL and simultaneous reduction of the sample spot area from a few mm2 down to 0.01 mm2, low attomole detection limits are obtained for bradykinin and cytochrome c. The detection limit in a single‐shot mass spectrum of bradykinin is estimated to be as low as 250 zeptomol. These are currently the lowest amounts of protein and the smallest volumes analyzed by MALDI‐MS.
Matrix‐assisted laser desorption mass spectrometry on a magnetic sector instrument fitted with an array detector
Authors: Bordoli Robert S. , Howes Kevin , Vickers Richard G. , Bateman Robert H. , Harvey David J. , Derrick P. J. 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization (MALDI) has been carried out on a high performance double‐focusing mass spectrometer fitted with an integrating focal plane array detector. High sensitivity (low femtomole detection) was obtained with peptides such as renin substrate. Underivatized complex oligosaccharides were also detectable at the 200 fmol level. The advantages of the array detector for improved resolution (5000 full width at half maximum) and the benefits in complex oligosaccharide and glycolipid analyses relative to MALDI time‐of‐flight (TOF) systems are shown. This improved resolution enabled ambiguities from the TOF data to be interpreted.
Microsecond pulsed glow discharge time‐of‐flight mass spectrometer
Authors: Hang Wei , Yang Pengyuan , Wang Xiaoru , Yang Chenglong , Su Yongxuan , Huang Benli 
Published: May 2005

AbstractA linear time‐of‐flight mass spectrometer (TOFMS) has been designed, constructed, and coupled with a glow discharge source in microsecond pulsed mode (MSPGD). Orthogonal acceleration, a DC quadrupole and deflecting pulse techniques are used to diminish kinetic distribution and the spatial distribution of ions, and for deflecting Ar+ ions in their flight path. Comparison was made in the same discharge source between MSPGD and DC discharge. The continuous ion current is only 0.2 nA in the DC discharge mode, while the peak ion current reaches over 100 nA in the MSPGD mode. In addition, the ratio of the repelled ions to total ions is much higher in MSPGD than with a DC discharge in TOFMS. The mechanism of MSPGD is discussed. A resolving power of 500 was achieved, which is excellent for elemental analysis. To the authors' knowledge, this is the first time that a MSPGD‐TOFMS combination has been described. The system is now being further optimized to improve its performance.
On‐line buffer removal and fraction selection in gradient capillary high‐performance liquid chromatography prior to electrospray mass spectrometry of peptides and proteins
Authors: Roboz John , Yu Qitao , Meng Ankuo , Van Soest Remco , Aplin Robin 
Published: May 2005

AbstractThe technique for on‐line removal of buffers and for fraction selection to eliminate source clogging and suppression of electrospray ionization by unwanted constituents consisted of: (i) selecting the initial mobile phase composition to retain analytes on top of a capillary high‐performance liquid chromatography (HPLC) column; (ii) washing the buffer isocratically to waste, using a two‐way micro dump valve; (iii) starting the gradient and switching the dump valve to introduce analytes into the source. Peptide and protein mixtures were prepared in 0.05–0.5 M phosphate and 0.55 mM tris‐based buffers, and water. After buffer removal, chromatograms and electrospray spectra were indistinguishable from those of aqueous controls, down to 1 pmol (acidic fibroblast growth factor) consumed, and up to 78 kDa (bovine transferrin) molecular weight. Aided by the dump valve, 100 fmol of angiotensin could be fractionated and identified on the slope of a 10 × 106 fmol of leucine enkephalin HPLC peak. On‐line buffer removal and fraction selection eliminate the need for additional preparation steps than can lead to excessive sample losses.
Mass spectrometry of some imidazoles of pharmacological interest
Authors: Rizzi Emanuele , Ferrario Francesco , Sala Alberto , Catinella Silvia , Traldi Pietro 
Published: May 2005

AbstractThe electron‐impact induced fragmentation processes of nine differently N‐substituted imidazoles were studied by means of mass‐analyzed ion kinetic energy spectrometry. The compounds under study show a mass spectrometric behaviour different from that observed for other imidazoles already studied. In fact all the observed decompositions are related to the substituent chains.
Matrix‐assisted laser desorption/ionization capabilities in the study of non‐enzymatic protein glycation
Authors: Lapolla Annunziata , Fedele Domenico , Seraglia Roberta , Catinella Silvia , Traldi Pietro 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization mass spectrometry has been succesfully applied in the study of non‐enzymatic glycation of different proteins. In the case of bovine serum albumin, glycated by in vitro experiments performed under pseudophysiological conditions, a clear increase in molecular weight is observed with respect to both glucose concentrations and incubation time. The in vitro glycation of ribonuclease with glucose and fructose shows some peculiar differences either in terms of the number of condensed sugar molecules or in terms of the reaction kinetics. The same approach, applied to plasma proteins of healthy and diabetic subjects, provides evidence for the occurence of glycation of human serum albumin for the latter subjects.
Investigation of matrices for fast‐atom bombardment mass spectrometry of fullerenes
Authors: Zhongping Yao , Hanhui Wen , Qingmin Zha , Shankai Zhao 
Published: May 2005

AbstractPhthalates (dimethyl, diethyl, dibutyl, diallyl and dinonyl) and p‐toluenesulfonates (methyl and ethyl) have been investigated as matrices for the fast‐atom bombardment mass spectrometric analysis of fullerenes for the first time. Compared with spectra obtained using 3‐nitrobenzyl alcohol and 2‐nitrophenyl octylether as matrices, the fast‐atom bombardment mass spectra of fullerenes with the two classes of compounds listed above as matrices are simple and show no fragment ions or adduct ions of fullerenes, and the matrices produce no background interference in the mass range of fullerenes.
Optimization by mass spectrometry of a tryptophan‐specific protein cleavage reaction
Authors: Vestling Martha M. , Kelly Michele A. , Fenselau Catherine , Costello Catherine E. 
Published: May 2005

AbstractMass spectrometry has been used to define the reaction of BNPS‐skatole (3‐bromo‐3‐methyl‐2‐(o‐nitrophenylsulfenyl)indolenine) with selected proteins and peptides, confirming the cleavage of the protein chain at tryptophan residues, characterizing the products, and identifying the side reactions. A short procedure for carrying out the cleavage reaction with minimal side reactions is presented.
Characterization of coal by matrix‐assisted laser desorption mass spectrometry. II. Pyrolysis tars and liquefaction extracts from the argonne coal samples
Authors: Herod Alan A. , Li Chun‐Zhu , Xu Bin , Parker John E. , Johnson Chris A. F. , John Phillip , Smith Gerry P. , Humphrey Paul , Chapman John R. , Kandiyoti Rafael , Games D. E. 
Published: May 2005

AbstractCoal pyrolysis tars and liquefaction extracts prepared from the set of eight Argonne coal samples have been characterized by MALDI‐MS. A Kratos Kompact MALDI III linear time‐of‐flight mass spectrometer was used, with a nitrogen laser operating at 337 nm and sinapinic acid as matrix. Spectra were collected by summing 50 laser pulses at low laser fluence to avoid fragmentation of desorbed ions. At low mass, 200–500 u, spectra from the pyrolysis tars and liquefaction extracts showed common features: intense peaks originating from the sinapinic acid matrix, m/z 205, 224 and 246, and, a range of peaks in the mass range from about 250 u to 400 u, which probably corresponds to overlapping homologous series of apparently polar material. A peak of ion intensity between 1000 and 5000 u was systematically observed, which was sample dependent and not always similar for the tar and extract prepared from the same coal. At high masses, separate trends were observed for coal pyrolysis tars and liquefaction extracts: molar mass ranges of pyrolysis tars were smaller, and showed no particular trend with carbon content of the original coal; these findings are consistent with size‐exclusion chromatography derived findings. Spectra of liquefaction extracts extended over wider ranges of molar masses and increased with increasing coal rank; the highest masses extended to 50 000u. Overall, pyrolysis tars appeared structurally different from liquefaction extracts and more difficult to desorb. The effect of changes in laser fluence and ion extraction voltage on mass spectra have been investigated: high‐mass regions of the spectra were found to be very sensitive to the magnitude of the ion extraction voltage. No carbon clusters or fullerene structures were detected.
Sequence‐ion enhancement of peptides digested with proteinase K
Authors: Li Xiao‐Ling , Yang Hou‐Jun , Grotemeyer Jürgen 
Published: May 2005

AbstractProteinase K has been employed to proteolyze peptides before their mass spectrometric analysis. This combination of the two methods yields abundant sequence ions in the mass spectrum, thus leading to an easy prediction of the primary structure of the peptide. It was found that both the variety of available sequence ions and also their abundances are increased strongly after proteinase K digestion, when compared with the normal mass spectrum. The shortcoming of little fragmentation encountered using conventional mass spectrometric ionization methods can mostly be overcome. The H′n and Y"m ions produced from proteolysis provided a double check of the peptide sequence.
Isotopic fractionation in secondary ionization mass spectrometry
Authors: Lyon Ian C. , Saxton John M. , Turner Grenville , Hinton Richard 
Published: May 2005

AbstractWe have studied isotopic fractionation effects which occur during the analysis of oxygen isotope ratios by secondary ionization mass spectrometry. Variable instrumental isotopic fractionation has been well documented in the past as making reliable ion microprobe analyses of oxygen isotopes elusive. We report here techniques for minimizing these effects by careful optimization of an Isolab 54 ion microprobe and a method of integrating the secondary‐ion beam to eliminate a major source of fractionation caused by unequal focusing of isotopes on the source slit of the mass spectrometer. A further improvement has been the installation of new ion detectors for measuring 18O− and 17O− secondary ion beams in which the ions strike a conversion dynode (Conversion dynode system—CDS) to release electrons into a channeltron. The CDS detectors have a uniform, high and stable gain which, coupled with the beam integration techniques referred to above, yield reproducible oxygen isotope ratios on both conducting and insulating mineral standards (⩽1.2‰ on 18O/16O during a day and <2‰ over periods of days and weeks).
Electron ionization fragmentation of some isoindolone derivatives
Authors: Mäki Esa , Csende Ferenc , Stájer Géza , Vainiotalo Pirjo , Pihlaja Kalevi 
Published: May 2005

AbstractThe electron ionization mass spectra of eleven isoindolone derivatives are reported. The molecular ions of these compounds were stable, some of them even very abundant (8–29% of the total ion current). There were many ions common to all or most of the compounds studied, although the abundances varied markedly from case to case. The base peak varied also from compound to compound. The most important ions common to almost every compound were [M—(CH2)iXH]+ (ions ai; i=1–4), [M—C7H7]+ (ion b) and the ion pattern [c—H], c and [c + H] corresponding to the loss of fused carbocycle together with the carbonyl function. These ions are caused by α‐cleavages and inductive dissociations of the bonds of the molecular ion in respect to the hetero atoms X and/or N.
Does the observed mass in quadrupole mass filters operated under standard analytical conditions depend on isomeric ion structure?
Authors: Capron Laure , Rolando Christian , Sablier Michel 
Published: May 2005

AbstractRecently published results have reported that mass displacements, which could reach 0.34 u, were observed in a quadrupole mass filter. An interaction between the dipole moment of ions and the quadrupolar RF field was then proposed to explain these mass displacements. We were interested by such an access to ion structure and decided to reproduce these results. Two sets of experiments were performed using two single‐stage quadrupole mass spectrometers operated under standard analytical conditions. Studies of the influence of resolution, source pressure and presence of helium or polar gas in the quadrupole enclosure on potential mass displacement detection have been performed. Nevertheless, we never observed significant mass shifts.