bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linked scans of peptides and protein digests: Amino acid sequence determination of components of complex mixtures
Authors: Morris Howard R. , Chatterjee Ashraf , Panico Maria , Green Brian N. , da Silva Maria A. A. Almeida , Hartley Brian S. 
Published: May 2005

AbstractTwo‐sector linked‐scan analysis of an unpurified proteolytic digest of a pyruvate decarboxylase enzyme (60 000 Da) has allowed the discovery and assignment of an amino‐terminal post‐translational modification and processing event. A difference in amino acid sequence from that predicted by a recently published nucleotide sequence has also been found. These results illustrate both the use and considerable potential of linked‐scan methods for the analysis of complex biopolymer mixtures.
Sequence determination of multiply charged peptide molecular ions by electrospray–ionization tandem mass spectrometry
Authors: Barinaga Charles J. , Edmonds Charles G. , Udseth Harold R. , Smith Richard D. 
Published: May 2005

AbstractElectrospray ionization generates multiply charged peptide molecular ions which are efficiently dissociated by collision with a neutral gas to provide sequence‐specific daughter ions. The scope for application of this phenomenon is illustrated by the nearly complete sequencing of melittin (relative molecular mass (Mr) 2846.5) employing a tandem quadrupole mass spectrometer having a mass limit of m/z 1400.
The application of a membrane interface to on‐line mass spectrometric measurements of volatile compounds in aqueous solutions
Authors: Dheandhanoo Seksan , Dulak John 
Published: May 2005

AbstractA simply designed silicon rubber membrane interface was used as a gas/liquid separator. This technique is based on the selectivity of the membrane. The combination of the membrane interface and a quadrupole mass spectrometer results in a simple and inexpensive instrument which can be used for both quantitative and qualitative determination of volatile compounds in aqueous solution. The response of the membrane‐interface/mass spectrometer to several volatile organic compounds in water was investigated. The detection limit of this instrument can be as low as the sub ppm range with a response time of a few minutes.
The use of two different buffers for unequivocal molecular weight determination in liquid chromatography/thermospray mass spectrometry
Authors: Maeder H. 
Published: May 2005

AbstractHigh‐performance liquid chromatography (HPLC) in combination with thermospray mass spectrometry (LC/TSP‐MS) is an important method for molecular weight determination of unknown compounds. In addition to the well‐known ammonium acetate buffer (NH4OAc) the use of methylammonium acetate (CH3NH3OAc) in the positive‐ and ammonium formate (NH4OFo) in the negative‐ion mode is recommended. Performing a second run with these buffers, even from spectra with only one single quasimolecular ion, an unequivocal molecular weight can be obtained. For correct assignment, the shift in mass of the corresponding quasimolecular ions in each mode is used. Finally, the use of a second buffer greatly facilitates the recognition of superimposed HPLC peaks.
Fragmentation of 2‐Acylcyclohexane‐1,3‐dione Ions and Their 4‐hydroxy derivatives. Elimination of water via an enol
Authors: Mudd A. 
Published: May 2005

Abstract2‐Acylcyclohexane‐1,3‐diones and their 4‐hydroxy analogues were analysed by gas chromatography/mass spectrometry. Fragmentation pathways for the formation of diagnostic ions are suggested.
Elucidation of some fragmentations of small peptides using sequential mass spectrometry on a hybrid instrument
Authors: Thorne Gareth C. , Gaskell Simon J. , Gross M. L. 
Published: May 2005

AbstractSequential daughter‐ion‐scanning analyses of small peptides have been performed using a hybrid tandem instrument of BEqQ configuration. Precursor ions are selected by B and allowed or induced (by high‐energy collisional activation) to decompose in the region preceding E. Decoupling of E from the accelerating voltage permits the selection of the first‐generation daughter ion whilst retaining appropriate float voltages for the quadrupole assemblies. The daughter ion selected by E is further subjected to low‐energy collisional‐activation dissociation (CAD) in q and the fragment‐ion spectrum is obtained by scanning Q. The sequential daughter‐ion‐scanning technique has been used to establish that ‘internal’ fragments of the types, (AY′) and (BY′), are formed via initial Y‐type cleavage. Fragmentation of a protonated peptide (angiotensin III) by loss of the C‐terminal amino acid residue, yielding a (B + OH) ion, is reported for the first time. This process is analogous to that previously described for metal‐cationized peptides.
Extending the mass range of the quadrupole ion trap using axial modulation
Authors: Kaiser Raymond E. , Louris John N. , Amy Jonathan W. , Cooks R. Graham , Hunt D. F. 
Published: May 2005

AbstractSecondary‐ion mass spectrometry, using Cs+ ion bombardment of solid and liquid matrices, has been implemented on a quadrupole ion trap. Tetraalkylammonium cations and protonated peptides, generated in an external source using a pulsed primary‐ion beam, are injected into the ion trap where they are decelerated and trapped in the course of collisions with the helium bath gas. The contents of the trap are then examined by recording a mass spectrum using the mass‐selective instability scan. To improve performance in the examination of these trapped ions, the technique of axial modulation is used to cause resonance ejection of ions from the trap during the mass‐analysis step. The supplementary AC voltage applied to the end‐caps causes resonant ejection of ions at qz values below those which correspond to the normal stability limit. This is demonstrated to increase the mass limit of a commercial ion trap from 650 Da to approximately 1300 Da with no loss in resolution or sensitivity, and to more than 20 000 Da at reduced sensitivity.
Use of gas chromatography/mass spectrometry selected‐ion recording for sterol content pattern recognition in fungal classification
Authors: Howell S. A. , Noble W. C. , Mallet A. I. , Minnikin D. E. 
Published: May 2005

AbstractChemotaxonomic studies are frequently limited by the volume of data obtained and the difficulty of reducing this to statistically interpretable results. This paper describes the use of a straightforward procedure for relating the pattern of occurrence of sterols in fungi, analysed by mass spectrometry, to their classification.
Loss of oligomer information in pyrolysis‐desorption/chemical‐ionization mass spectrometry of amylose, due to the influence of potassium hydroxide
Authors: Scheijen Martin A. , Boon Jaap J. , van der Greef J. 
Published: May 2005

AbstractPyrolysis‐desorption/chemical‐ionisation mass spectrometry (PyD/CIMS), using ammonia as ionization gas, was employed to investigate the influence of potassium hydroxide on the pyrolytic behaviour of glucans. The mass spectrum of native amylose, a 1 → 4 linked α‐D‐glucan, revealed an ion series pointing to desorption of intact 1,6‐anhydro‐oligosaccharides. Ions indicating oligomers up to the nonamer were observed. Addition of trace amounts of potassium hydroxide to amylose resulted in reduction in the size of the 1,6‐anhydro‐oligosaccharide ions and a simultaneous increase of ions resulting from ring rearrangements. Larger amounts of potassium hydroxide led to a complete loss of mass spectral information at the oligomer level.Similar mass spectrometric distributions in the PyD/CIMS data of a potassium hydroxide extracted tobacco fraction clearly reveal that alkali remnants must be present in this sample, which severly reduce the mass spectrometric information from polysaccharide oligomers. It is important to evaluate the role of inorganics on the thermal activation and subsequent fragmentation of biopolymers in PyD/CIMS experiments.
Laser‐induced desorption of proteins
Authors: Salehpour M. , Perera I. , Kjellberg J. , Hedin A. , Islamian M. A. , Håkansson P. , Sundqvist B. U. R. 
Published: May 2005

AbstractLaser‐induced desorption mass spectrometry has been applied to a number of proteins in the mass range 5000–150 000 u. The beam from an excimer‐laser‐pumped dye‐laser at 266 nm has been focused to a spot of about 50 μm in diameter with irradiances in the 107W/cm2 region. A linear time‐of‐flight mass spectrometer has been used for mass spectrometric measurements, where positive and negative secondary ions of large proteins have been studied. The effect of different experimental parameters on the protein ion‐signal intensities are discussed.
Characterization of phosphorylated amino acids by fast‐atom bombardment mass spectrometry
Authors: Dass Chhabil 
Published: May 2005

AbstractPositive‐ and negative‐ion fast‐atom bombardment (FAB) mass spectrometry and linked‐field scan techniques at constant B/E are used to characterize phosphorylated serine, threonine, and tyrosine amino acids. Abundant molecular ions are formed for all three amino acids in both modes of ionization. The dominant fragmentation is cleavage of the phosphate ester bond with charge retention in positive‐ion FAB by the amino acid backbone and in the negative‐ion mode by the phosphate group. The unique feature of positive‐ion FAB mass spectra of phosphoserine and ‐threonine is the loss, from the ion [M+H]+, of a molecule of phosphoric acid (98 Da), whereas the corresponding tyrosine expels a HPO4 (96 Da) moiety to yield a stable phenylalanine ion.
Collision‐induced dissociation of Cs4I. An Example of Superelastic Collisions?
Authors: Alexander A. J. , Thibault P. , Boyd R. K. 
Published: May 2005

AbstractThe collision‐induced dissociation (CID) of Cs4I to form Cs3I has been investigated by mass‐analysed ion kinetic energy spectroscopy, When helium was used as collision gas the CID process was accompanied by sizable loss of translational energy in the collisional‐activation step. However, use of krypton or xenon as collision gas yielded product ions with translational energies higher than that observed for unimolecular reaction in the absence of collision gas. Neon and argon provided intermediate behaviour. Extensive experiments designed to investigate possible explanations for these observations left superelastic collisions of an excited state as the only possibility. Since nothing is known about the structures and electronic states of species like Cs4I, the necessarily speculative discussion is based upon general considerations of coupling of translational and electronic energies via crossings between states of the transitory collision complex. These observations emphasise the complexity of the possible processes which can occur as a result of collisions in the keV range.
A simple and effective way to enhanee fast‐atom bombardment mass spectra of sulfonic acids
Authors: Shimanskas Charles , Ng Kenneth , Karliner Jerrold 
Published: May 2005

AbstractA technique for the simplification of fast‐atom bombardment (FAB) spectra of polysulfonic acids, especially azo dyes complicated by sodium, is discussed. The sodium may be present as the sulfonate salt or the salt may be formed during FAB analysis from impurities present in the sample. The incorporated sodium as well as other impurities which may be present in commercial samples are removed by means of a simple cationic‐exchange‐resin procedure, yielding simplified and unambiguous FAB spectra of the sodium‐free material.
Observation of sequence‐specific peptide fragmentation using extended tandem mass spectrometry experiments
Authors: Schey Kevin L. , Schwartz Jae C. , Cooks R. Graham , Caprioli R. M. 
Published: May 2005

AbstractReaction‐intermediate spectra are reported for peptide mixtures using a hybrid BEQQ and a pentaquadrupole mass spectrometer. In this extended tandem mass spectrometry scan, the protonated molecule and a terminal fragment ion are selected with the first and third mass analyzers, respectively. A subsequent linked scan at constant B/E (hybrid instrument) or a scan of the middle quadrupole (pentaquadrupole instrument) produces the reaction‐intermediate spectrum. The resulting spectra are simpler than conventional tandem mass spectrometry daughter‐ion spectra and display only sequence ions of one group, viz. A, B and C or X, Y and Z. This information facilitates structural elucidation and is obtainable on nanomole amounts of peptide.
Direct synthesis and electron‐ionization positive‐ion mass spectrum of tetrakis(acetylacetonato)cerium(IV), Ce(C5H7O2)4
Authors: Chaudhuri Mihir K. , Islam Nashreen S. , Khathing Darlando T. , Shylla Vicky G. , Mathur D. 
Published: May 2005

AbstractCrystalline Ce(C5H7O2)4 has been synthesized directly from the reaction of hydrated cerium(IV) oxide with acetylacetone, (C5H8O2), and its electron‐ionization (EI) mass spectrom is reported. The compound exists as a monomer (mass 536) in the gaseous state. The mass spectrum, like those of M(C5H7O2)4 (M = Zr or Th) and CeL4 (L = fluorinated β‐diketonate), shows the dominant ion signal to be due to the [Ce(C5H7O2)3]+ ion that arises from the loss of one C5H7O2 from the molecular ion. An internal electron‐transfer affords [Ce(C5H7O2)3]+˙. Fragmentation of [Ce(C5H7O2)3]+˙ to [Ce(C5H7O2)2]+ is similar to that observed for the tris‐chelates of trivalent transition metals and La(C5H7O2)3. The ion [Ce(C5H7O2)2]+ ultimately breaks down to [CeO]+ through the sequential loss of three even‐electron neutral species, CH3COCHCCH2, H2O and CH3COCHCCH2 without invoking any further reduction of the Ce centre. Mechanisms are given for the loss of the three even‐electron species from the bis(acetylacetonato)cerium(III) ion fragment. Theoretical simulations of patterns of the fragment ions [Ce(C5H7O2)3]+˙, [Ce(C5H7O2)2]+˙, and [Ce(C5H7O2)OH]+ have been made and compared with those of the corresponding experimental results in support of the suggested mode of fragmentation.
Transmission characteristics of a radio‐frequency‐only quadrupole gas‐collision cell at high axial energies in a hybrid tandem mass spectrometer
Authors: Alexander A. J. , Dyer E. W. , Boyd R. K. 
Published: May 2005

AbstractCollision induced dissociation (CID) experiments using RF‐only quadrupole collision cells normally employ laboratory‐frame collision energies Elab of a few tens of eV. Difficulties in inducing CID reactions for larger precursors (> 600–800 Da) can be attributed in part to collision energies, in the appropriate centre‐of‐mass reference frame, which are too low. Attempts to overcome this problem by using values of Elab in the range of a few hundreds of eV have been largely unsuccessful. The present work shows that a major reason for this lack of success has been an inability of the instruments used to fulfil the focusing requirements of an RF‐only quadrupole cell for such precursors, and their higher mass fragments, in this range of values for Elab. A simple modification permitting use of much higher values of the RF amplitude has been shown to permit the collision cell to be operated so that the ion‐beam profile at the entrance aperture is imaged at the exit; improvements in precursor transmission efficiency by up to two orders of magnitude are thus obtainable. Examples of corresponding improvements in fragment‐ion spectra of a test octapeptide are also demonstrated. The principal drawback of this approach concerns the poor transmission for low‐mass fragments near the stability cut‐off (Mathieu parameter qu > 0.91); reasons for the non‐zero transmission efficiency for fragments with qu > 0.91 are discussed, together with methods for alleviating the low‐mass transmission problem.
Instrument‐independent database for collisionally activated dissociation in RF‐only quadrupoles. The case of C2H3O+ and C3H
Authors: Martinez Richard I. , Ganguli B. 
Published: May 2005

AbstractDynamically correct (i.e., instrument‐independent) branching ratios can be measured under single‐collision conditions in tandem mass spectrometers incorporating RF‐only quadrupole collision cells. The absolute branching ratios were measured as a function of the center‐of‐mass interaction energy ECM for the collisionally activated dissociation (CAD) of CH3CO+ (m/z43) from several source compounds (ethanol, oxirane), and CH3CO‐X (where X = H, CH3, CH3CH2, CH3CO, CH3COCH2, and C6H5)). The energy dependences of the branching ratios for C2H3O+ from CH3CO‐X source compounds are quite distinct from those observed for C2H3O+ from ethanol or ethylene oxide, or for the C3H+7 ions (also m/z 43) from n‐pentane. Hence, one can use the CAD of m/z 43 to distinguish CH3CO‐X compounds from other source compounds, including sources of C3H7+ ions. Therefore, the characteristic branching ratios of ionic substructures may provide for tandem mass spectrometry a „fingerprinting”︁ capability analogous to the use of group frequencies in infrared spectroscopy.
Electron ionization mass spectrometry for sequence analysis of glycosphingolipid mixtures by fractional evaporation in the ion source. Mass spectrometric evidence for an eleven‐sugar glycolipid
Authors: Holgersson J. , Pimlott W. , Samuelsson B. E. , Breimer M. E. 
Published: May 2005

AbstractThis paper describes the use of electron ionization mass spectrometry for structural characterization of a mixture of glycosphingolipids from a single human kidney and presents mass spectrometric evidence for the presence of an eleven‐sugar glycolipid. A large amount of structural information is obtained from minor glycolipid constituents having long sugar chains by a fractional evaporation in the ion source, achieved by steadily increasing the ion‐source temperature.
Structural characterization of two isomeric dimethoxyindoles of biological interest, using high‐ and low‐energy collisional spectroscopy
Authors: Emary W. Bart , Allegri G. , Costa C. , Frison G. , Traldi P. 
Published: May 2005

AbstractIt is not possible to distinguish isomers of biologically important dimethoxyindoles using electron‐ionization mass spectra, but they may be distinguished by collisionally activated dissociation. In particular, energy‐resolved mass spectrometry yields the best data for distinguishing between these isomers.
Ion optical considerations of a quadrupole–octapole lens system for varying mass range on a simultaneous detector
Authors: Ishihara Morio , Kammei Yoshihiro , Matsuo Takekiyo 
Published: May 2005

AbstractThe sensitivity and mass resolution of a conventional double‐focusing mass spectrometer equipped with an array detector are limited by the fixed range of masses that can be detected simultaneously. This paper describes ion‐optical properties of a new lens system for varying the relative mass range on the simultaneous detector.
Matrix‐assisted laser‐desorption mass spectrometry using 355 nm radiation
Authors: Beavis Ronald C. , Chait Brian T. , Standing K. G. 
Published: May 2005

AbstractMatrix‐assisted laser desorption of proteins with the 355 nm frequency‐tripled output of a neodymium:yttrium‐aluminium‐garnet laser has been demonstrated. In order to produce desorption at this wavelength, the cinnamic acid derivatives ferulic, caffeic and sinapinic acids have been employed as matrices. Excellent sensitivity (routinely one pmol of protein) and good mass resolution (m/Δm 400, Full width at half maximum) have been obtained by this new method. Ultraviolet photo‐spectrometry of the cinnamic acid derivative matrices suggests strongly that they can be used as protein laser‐desorption matrices at any wavelength between 260 nm and 360 nm, allowing the development of laser‐desorption mass spectrometers based on nitrogen or excimer lasers.
The dissociative ionization of H2 by electrons
Authors: Krishnakumar E. , Mathur D. 
Published: May 2005

AbstractDissociative ionization of H2 by low‐energy monoenergetic electrons has been studied in a crossed electron‐beam/molecular‐beam apparatus incorporating a quadrupole mass spectrometer with a view to examining the influence, if any, of the quadrupole RF fields on neutral Rydberg species, the associated physical mechanisms and their effect on H+ kinetic‐energy distribution functions.
Discrimination effects in inorganic ion‐cluster detection by secondary‐electron multiplier in mass spectrometry experiments
Authors: Alexandrov M. L. , Gall L. N. , Krasnov N. V. , Lokshin L. R. , Chuprikov A. V. 
Published: May 2005

AbstractDiscrimination effects in secondary electron multipliers due to the differences in kinetic energy with which ions of different masses strike the dynode surface are investigated. The threshold energy at which ions of a particular mass can be detected is discussed. The efficiencies of such multipliers when used with cluster ions such as H+(H2O)N (where Cat+ represents an alkali‐metal cation) are investigated and discussed, in terms of both the ‘kinetic’ and ‘potential’ emission coefficients.
Abnormal effects in the detection of ions from bioorganic substances by mass spectrometry
Authors: Alexandrov M. L. , Gall L. N. , Krasnov N. V. , Lokshin L. R. , Chuprikov A. V. 
Published: May 2005

AbstractThe characteristics of the detection of ions of the alkali metals and of cluster ions of the type (H2O)NMH+ (where M is an amino acid) are markedly different from those for the detection of protonated saccharose ions. The latter are shown to produce a signal from a secondary electron multiplier detector at a lower ion energy than the threshold energy for the former ions. An explanation is proposed in terms of the charge localization.
Negative‐ion chemical ionization spectra of oxazolidinone derivatives of amino acids prepared by their reaction with dichlorotetrafluoroacetone
Authors: Macfarlane R. G. , Watson D. G. , Midgley J. M. 
Published: May 2005

AbstractOxazolidinone derivatives of glycine, phenylalanine and tyrosine were prepared by their reaction with dichlorotetrafluoroacetone. The derivatives were analyzed by gas chromatography/negative‐ion chemicalionization mass spectrometry with methane as the reagent gas. The mass spectra under these conditions were composed of a few ions resulting largely from the addition of a chlorine radical to the molecular ion and successive losses of up to two HCl moieties from the molecular ion; loss of CO2 was also observed. Comparison of the mass spectrum of glycine and [2H2]glycine indicated that the protons involved in the loss of HCl from the molecular ion were derived in the first instance from the CH2 group in the derivative and secondly from the NH group. The derivatives were applied to the analysis of the amino acid precursors of biogenic amines in nervous tissue from the locust.
Internal energy effects in the collision‐induced dissociation of large biopolymer molecular ions produced by electrospray ionization tandem mass spectrometry of cytochrome c
Authors: Smith Richard D. , Barinaga Charles J. 
Published: May 2005

AbstractThe effects of internal energy upon metastable and collision‐induced dissociation (CID) processes observed in the tandem mass spectrometry of multiply protonated molecules of horse‐heart cytochrome c (Mr 12360) are described. The internal energy of the multiply protonated (15H+) molecules (at m/z 825) formed by electrospray ionization (ESI) was manipulated using electric fields in the atmospheric pressure/vacuum interface region. Highly efficient CID is obtained for molecular ions collisionally activated in the ESI interface. The dissociation efficiency at 3.8 eV to 5.8 eV (center of mass) collision energies for internally “hot” molecular ions under multiple collision conditions in a triple quadrupole mass spectrometer is shown to be much greater than for “cold” ions. The CID spectra show dramatic effects due to internal energy, with charge stripping dominating for cold ions (where CID efficiency is very low) and extensive fragmentation observed for hot ions.
Lowering detection limits in plasma‐desorption mass spectrometry by partial target shielding
Authors: van Veelen P. A. , Tjaden U. R. , van der Greef J. 
Published: May 2005

AbstractA simple method of improving signal‐to‐noise ratios in plasma‐desorption mass spectrometry of femtomole quantities is described. Background reduction is achieved by effectively shielding of the non‐sample area. It is shown that detection limits can be improved by a factor of 4.