bluuebunny/crossref_metadata_2025 huggingface dataset:
Accurate ion abundance measurements in ion cyclotron resonance mass spectrometry by linear prediction
Authors: Loo J. F. , Krahling M. D. , Farrar T. C.
Published: May 2005

In standard pulsed ion cyclotron resonance mass spectrometry (ICRMS) mass spectra are generated by converting the time domain signal to the frequency or mass domain by fast Fourier transform (FFT). The FFT requires long acquisition times to acquire high resolution mass spectra. In ICRMS, long acquisition times introduce distortions in the peak intensities of the transformed spectrum that lead to errors in ion abundance. We report here the use of linear prediction methods on data sets collected during much shorter acquisition times to determine actual ion abundances more accurately.
The detection of large molecules in matrix‐assisted UV‐laser desorption
Authors: Spengler Bernhard , Kirsch Dieter , Kaufmann Raimund , Karas Michael , Hillenkamp Franz , Giessmann Ulrich
Published: May 2005

Mechanisms related to high‐mass ion detection were studied using matrix‐assisted UV laser desorption for ion generation and a tandem (MS/MS) time‐of‐flight mass spectrometer for the analysis of secondary species formed at the conversion dynodes. Secondary‐electron emission was found to be less pronounced with increasing molecular weight. Instead small secondary ions generated by collision of primary ions with the conversion dynodes appeared to be the dominant process for the detection of ions of masses up to several hundred thousand Da. The use of microchannel plate detectors has been shown to become less effective for high molecular weight applications. Mass spectra of secondary ions emitted from a conversion dynode bombarded with keV primary ions have been recorded. Regardless of the composition of the primary molecules, the secondary mass spectra were similar. Sputtering of surface adsorbates is assumed to be the major mechanism of secondary ion formation, rather than surface induced dissociation or fragmentation of the primary ions.
Ion‐trap mass spectrometry in ion structure studies. 1. Characterization of isomeric hydroxyindoles by electron ionization and energy‐resolved collision‐activated mass spectrometry
Authors: Evans Catherine , Catinella Silvia , Traldi Pietro , Vettori Umberto , Allegri Graziella
Published: May 2005

Three hydroxyindole isomers were investigated by conventional electron ionization (EI) mass spectrometry and by collision‐activation (CA) experiments. Although the EI mass spectra of the three isomers are virtually superimposable, 3‐hydroxyindole can easily be differentiated from the others by single‐energy collision spectroscopy. Only by energy‐resolved mass spectrometry (ERMS) could the characterization of the 4‐ and 5‐ hydroxyindole isomers be achieved. ERMS, which in the ion‐trap mass spectrometer can be performed by different methods, was achieved by changing both the AC supplementary voltage and the βz value at which the collision experiments were performed. The first method proved to be the most effective in the present case. Further collision experiments, carried out at a range of AC voltage durations did not yield energy‐resolved data.
The characterization of polystyrene oligomers by field‐desorption mass spectrometry
Authors: Rollins K. , Scrivens J. H. , Taylor M. J. , Major H.
Published: May 2005

Field‐desorption mass spectrometry has been used to characterize polystyrene oligomers of molecular weight up to 15 000 Da. The technique shows good agreement with molecular weight data calculated using vapour‐phase osmometry and gel‐permeation chromatography but in addition provides much more detailed information in terms of oligomer distribution and the nature of end groups present in the oligomers.
A detailed study of the characteristics of the ion‐trap mass spectrometer using dynamically programmed scans
Authors: Penman A. D. , Todd J. F. J. , Thorner D. A. , Smith R. D.
Published: May 2005

The aims of the investigation were to use the method of dynamically programmed scans to study in detail some tandem mass spectrometric characteristics of the ion‐trap mass spectrometer and then to use the programs to investigate the possibility of performing benchtop gas chromatography/tandem mass spectrometry experiments on the standard instrument. In particular we have examined the effect of applying a DC ramp during the ‘tickle’ period as a means of broadening the range of resonant frequencies, thereby facilitating the tuning required to effect excitation.
Fast‐atom bombardment mass spectrometry and fast‐atom bombardment tandem mass spectrometry of some monosaccharide oximes
Authors: New A. P. , Haskins N. J. , Lee B.
Published: May 2005

The oximes of monosaccharides have not been well characterized by mass spectrometry. Conventional electron ionization (EI) experiments have supported the structures of these compounds but the data produced are usually equivocal (Finch and Merchant, JCS Perkin 1, 1682 (1975)). The application of fast‐atom bombardment mass spectrometry to monosaccharide oximes gives molecular weight information. However, little fragmentation is observed and it is not possible to distinguish between stereoisomers. Using fast‐atom bombardment tandem mass spectrometry experiments, we have produced daughter‐ion spectra which are sufficiently different to enable us to distinguish between the stereoisomers of the oximes of monosaccharides.
A fast‐atom bombardment tandem mass spectrometry screening procedure for the presence of involatile sulphonated dyestuff intermediates
Authors: Monaghan J. J. , Morden W. E.
Published: May 2005

The introduction of more rigorous regulations aimed at controlling the use of sulphonated dyestuffs and dyestuff intermediates has pointed to the need for screening methods for the presence of these involatile compounds. Although much work has been caried out recently on the mass spectrometric behaviour of these compounds, it has been concerned principally with the production of molecular weight information using novel ionization methods rather than with any attempt to obtain structurally diagnostic fragment ions. In this mass spectrometric investigation of a range of naphthalene sulphonic acid salts, positive‐ion and negative‐ion fast‐atom bombardment (FAB) mass spectra have been obtained and FAB‐tandem mass spectrometry (MS/MS) has been used to acquire spectra (daugher‐ion, parent‐ion and neutral‐loss) in an attempt to develop a useful screening method. On known compounds, best results were found when using a negative‐ion neutral‐loss scan to detect the loss of 64 mass units (corresponding to loss of SO2). This was confirmed by successful use of this scan to screen a sample of sulphonate residues.
Loss of H2 from metastable CH3SiH ions
Authors: Tobita Seiji , Nakajima Katsuyoshi , Tajima Susumu , Shigihara Atsushi
Published: May 2005

Unimolecular dissociations of metastable methylsilyl cations CH3SiH3+ are investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry. The predominant fragmentation is H2 loss which proceeds via at least two distinct mechanisms with substantially different kinetic energy releases. Their reaction mechanisms are inferred from the results of experiments and MNDO calculations. The MIKE spectrum of the deuterium‐labelled ion, CH3SiD2+ indicates that the H and D atoms are randomized before dissociation.
Variation of kinetic energy release and average internal energy with temperature and electron energy for unimolecular ionic transitions
Authors: Selim Ezzat T. M. , Rabbih M. A. , Fahmey M. A.
Published: May 2005

The kinetic energy released and the intensity ratios [m*]/[M]+ or [m*]/[F]+ (where m* is a metastable peak, and [M]+ and [F]+ are molecular‐ion and fragment‐ion peaks, respectively) for seven unimolecular ionic transitions generated from benzyl alcohol and benzylamine have been studied as a function of ion‐source temperature and ionizing electron energy. Only during HCN elimination from [C7H8N]+ fragment ion does the kinetic energy released and the intensity ratio [58.9]/[106]+ display a temperature dependence. On the other hand, the kinetic energy released during only two transitions, generated from benzyl alcohol, displays a significant electron‐energy dependence while the intensity ratios [m*]/[M]+ or [m*]/[F]+ for all the transitions studied exhibit marked decrease with decreasing electron energy starting at about 40 eV.
Mass spectrometric study of vaporization processes and thermodynamic properties in the GeO2·P2O5 system
Authors: Stolyarova V. L. , Shornikov S. I. , Ivanov G. G. , Shultz M. M.
Published: May 2005

The Knudsen effusion mass spectrometric method was used to study the vaporization processes and thermodynamic properties of the GeO2·P2O5 system at 1423 K. GeO, PO2, P4O10, GePO3 and O2 molecules were identified in the gas phase above the GeO2·P2O5 system. A correlation was shown between the phase diagram and the thermodynamic properties attained in the GeO2·P2O5 system.
Mass spectral characteristics of some 3,5‐disubstituted 4‐isoxazolecarboxylic acids
Authors: Maksimović Milka , Nikolin Ana , Nikolin Branko
Published: May 2005

Mass spectrometry has been applied for the structural study of some new unsymmetrically 3,5‐disubstituted 4‐isoxazolecarboxylic acids prepared by a modification of the general procedure of Quilico and Fusco. The new glucoside, 3‐[2‐(β‐D‐glucopyranosiloxy)‐5‐chlorophenyl]‐5‐methyl‐4‐isoxazolecarboxylic acid (1) and 3‐(2‐hydroxy‐3,5‐dichlrophenyl)‐5‐methyl‐4‐isoxazolecarboxylic acid (2) have been prepared starting from the glucoside helicin, 2‐(β‐D‐glucopyranosiloxy) benzaldehyde or the corresponding aglucon, the salicylaldehyde, respectively. Fragmentation patterns of 2 and its analogue 3‐(2‐hydroxy‐5‐chlorophenyl)‐5‐methyl‐4‐isoxazolecarboxylic acid (3), obtained by the cleavage of the glycosidic linkage of 1 are discussed. The principal fragmentation routes of these compounds are formulated to occur via azirine intermediates.
Diatomic monociations and dications containing germanium and a rare gas atom
Authors: Curtis Jonathan M. , Rong Lu‐Shan
Published: May 2005

Diatomic dications and monocations GeY2+ and GeY+˙, where Y = Ne, Ar, Kr or Xe, have been detected on the microsecond time scale. They are characterized via appearance energies, charge stripping of GeY+˙ ions, and mass‐analysed ion kinetic energy spectroscopy. The formation of GeAr+˙ is found to involve an excited state of Ar in a Hornbeck‐Molnar process.
Energy transfer limits in collisions with fast targets
Authors: Turecek Frantisek , Alexander Anthony J.
Published: May 2005

The kinematics of ion/neutral collisions are analysed in terms of projectile and target kinetic energies and relative velocities. High (keV) center‐of‐mass collision energies are achievable for high‐mass ions or neutrals colliding with keV target atoms, electrons or ions. The center‐of‐mass collision energy depends only very little on the fast‐target mass. Applications in collisionally‐activated dissociation of high‐mass ions and neutrals are discussed.
A collisional study of some C60 and C70 fullerene ions
Authors: Young Alex B. , Cousins Lisa M. , Harrison Alex G.
Published: May 2005

The high‐energy collision‐induced dissociation (CID) mass spectra of C, C, C, C and C are reported. In all cases, fragmentation occurs by loss of an even number of carbon atoms, in agreement with photodissociation studies of C and C. No charge‐separation reactions are observed for the multiply charged ions. Collision‐induced dissociation of C leads to a slight preference for formation of C, while dissociation of C and C shows a more pronounced preferenced for formation of C and C, respecstively. Under electron‐capture Chemical‐ionization conditions the fullerenes readily capture an electron to form the molecular anions. Collision‐induced dissociation of C and C leads to elimination of 1, 2 and 4 carbon atoms; the elimination of one carbon is unique among larger carbon cluster ions. Charges inversion of the molecular anions leads to formation of the respective molecular cations and fragementation of these cations by loss of an even number of carbon atoms. Formation of C is slightly preferred in the C case, while C is the most abundant ion in the charge inversion mass spectrum of C.
Electron ionization fragmentations of some N‐substituted 2‐N‐methylimino‐4,5‐tetramethyleneperhydro‐3, 1‐oxazines and related thiazines
Authors: Pihlaja Kalevi , Liukko‐Sipi Sirpa , Fülöp Ference , Bernáth Gábor , Vainiotalo Prijo
Published: May 2005

The 70 eV electron ionization mass spectra of six cyclohexane fused 2‐N‐methyliminoperhydro‐3,1‐oxazines and six related thiazines were recorded and their fragmentation behaviour studied by metastable‐ion analysis and exact mass measurement. For the unsubstituted compounds, decompositions which can be rationalized to start as a simple α‐cleavages with respect to the ring nitrogen atom were dominant. Many of these reactions were accompanied by a hydrogen‐atom transfer to the neutral fragment lost. N‐substitution prompted more extensive hydrogen migrations to take place, where hydrogen atoms were transferred to the heterocyclic part of the molecule. Only methyl‐substituted compounds showed remarkable sterochemical specificity, thus allowing isomeric differentiation to take place.
Standard reference spectra for tandem mass spectrometry quality assurance, performance evaluation and proficiency testing: Tandem mass spectrometers which use RF‐only multipole collision cells
Authors: Martinez Richard I. , Betowski Leon D.
Published: May 2005

The collisionally activated dissociation (CAD) of the acetone cation (m/z 58) can be used for quality assurance, performance evaluation, and proficiency testing of CAD measurements in tandem mass specstrometry (MS/MS) instruments which use RF‐only multipole collision cells. The absolute branching ratios (product distributions) of the CAD fragment ions, when measured as a function of the center‐of‐mass collision energy Ecm, can provide an objective basis for quality assurance whenever MS/MS methods are used (viz, to validate how well the target thickness, ion‐containment efficiency, and collision energy are being controlled in various instruments).
Continuous‐flow fast‐atom bombardment on an external‐ion‐source Fourier transform ion cyclotron resonance mass spectrometer
Authors: Watson C. H. , Kruppa G. , Wronka J. , Laukien F. H. , Van Binst G.
Published: May 2005

A continuous‐flow sample interface for fast‐atom bombardment has been developed for use on an external‐ion‐source Fourier transform ion‐cyclotron resonance mass specstrometer. The new interface provides a quick and convenient means for sample introduction. A suppression of common glycerol matrix ions was observed when compared to static analysis. High mass resolution, exact mass measurements, and tandem mass spectrometry spectra were obtained on a sample of Gramicidin S.
The realization of a low‐energy ion‐scattering technique with an ion cyclotron resonance spectrometer
Authors: Nikolaev E. N. , Mordehai A. V. , Frankevich V. E.
Published: May 2005

A low energy ion scattering technique for investigation of the first monolayer of a surface has been realized in an ion cyclotron resonance mass spectrometer. The secondary‐ion mass spectrometry mode is also available in the same configuration. Preliminary results are shown for the analysis of the metal surface of a magneto‐optical recording film.
Investigation of collisional‐activation decomposition process and spectra in the transport regions of an electrospray single‐quadrupole mass spectrometer
Authors: Voyksner Robert D. , Pack Terry
Published: May 2005

The use of collisional‐activation dissociation (CAD) in the electrospray region was evaluated for generating structural information on several pesticides and antibiotics. The collision energy used to generate the CAD spectra could be varied easily by changing the capillary/skimmer potential difference, imparting fromOeV to above 16 eV internal energy to the near thermal ions generated by electrospray, The internal energy distribution for low‐energy collisions (capillary/skimmer potential difference of 20 V) closely matches the curves generated by a triple‐quadrupole mass spectrometer. Furthermore, the CAD spectra for selected compounds generated by electrospray in the transport region at a capillary/skimmer potential differences of 30–50 V closly resembled those obtained from the [M + H]+ ion by a triple quadrupole using 30eV collision energy. The CAD of ions in the transport region resulted in 70% to 80% daughter‐ion yields and minimal loss in overall ion current compared to the ion current for protonated or cationized parent molecules. The major daughter ions for 10 pg of Aldicarb and penicillin G could be detected (signal‐to‐noise ratio>5) under full‐scan CAD conditions.
Comparison of intensities between doubly charged ions [M+2H]2+ and singly charged ions [M+H]+ of gramicidin S by electrospray mass spectrometry
Authors: Sakairi Minoru , Yergey Alfred L.
Published: May 2005

The reason why the intensity of doubly charged ions [M+2H]2+ of gramicidin S is higher than that of singly charged ions [M+H]+ in electrospray is investigated by ion evaporation theory. As a result of comparison between the total free energies of extracting [M+2H]2+ and [M+H]+ from a charged droplet to infinity, it is found that the total free energy of [M+2H]2+ is estimated to be lower than that of [M+H]+. This clearly supports the experimental result. In addition, the importance of the electrostatic contribution in electrospray is demonstrtated by showing the result that the total free energy of [M+2H]2+ without electrostatic contribution is higher than that of [M+H]+.
Four interfaces for liquid chromatography/atmospheric‐pressure‐ionization mass spectrometry
Authors: Sakairi Minoru , Yergey Alfred L.
Published: May 2005

Mixture analyses are demonstrated using the liquid chromatograph/atmospheric‐pressure‐ionization mass spectrometric system with four modes. These modes are atmospheric‐pressure spray with electron ionization, atmospheric‐pressure chemical ionization, atmospheric‐pressure spray ionization, and electrospray ionization modes. This system can deal with a wide variety of compounds from hydrocarbons with low polarity to proteins with high polarity.
High mass material (>104 daltons) in a coal liquefaction extract, by laser‐desorption mass spectrometry
Authors: John P. , Johnson C. A. F. , Parker J. E. , Smith G. P. , Herod A. A. , Gaines A. F. , Li C.‐Z. , Kandiyoti R.
Published: May 2005

The use of a laser‐desorption mass spectrometer to examine a coal liquefaction extract known to contain high‐molecular‐mass material (from size‐exclusion chromatography) has shown the presence of components of molecular mass in excess of 104Da for the first time. The molecules detected differ from each other in molecular mass by a few hundred or a few thousand Da. These preliminary results indicate that the basic coal‐structure molecules probably consist of aromatic clusters on a chin, in reasonable agreement with current theories of coal structure.
A kinetic method of distinguishing isomeric C3H cations
Authors: Riveros José M. , Zhu Zhiqing
Published: May 2005

A method is described of studying ion/molecule kinetics in a Fourier‐transform ion cyclotron resonance spectrometer of ions produced at precursor pressures of 6 × 10−9 mBar with a neutral gas introduced through a pressure pulse of variable time. The analysis of the kinetic curves of the proton‐transfer reactions of C3H cations to CH3OH yields either single or double exponential decays that can readily be used to obtain the percentages of allyl and 2‐propenyl cations produced by different precursors. Allyl bromide is shown to produce 100% allyl cations while 2‐bromopropene at 13 eV yields roughly 74% of 2‐propenyl and 26% of allyl cations.
Mass‐specific selection of ions in Fourier‐transform ion cyclotron resonance mass spectrometry. Unintentional off‐resonance cyclotron excitation of selected ions
Authors: Heck Albert J. R. , de Koning Leo J. , Pinkse Frans A. , Nibbering Nico M. M.
Published: May 2005

Mass‐specific selection of ions in Fourier‐transform ion cyclotron resonance (FT‐ICR) ion trap is shown to be hampered by unavoidable off‐resonance cyclotron exctron excitation of the ions to be selected. This unintentional off‐resonance cyclotron excitation is caused by radio‐frequency fields which are applied during the selection procedure to eject unwanted ions by on‐resonance excitationof their cyclotron motion. The experimental results indicate that the effective cyclotron motion of the ions subjected to an off‐resonance single‐frequency RF field is alternatingly excited and de‐excited with a periodicity equal to 2π/(ω0−ωeff), where ω0is the frequency of the excitation field and ωeff is the effective ion cyclotron frequency. Furthermore, it has been demonstrated that the translational energy gained during off‐resonance cyclotron excitation can be predicted quantitatively by theory. The net translational energy can be minimized below 1 eV if the duration of the individual single‐rfrequency excitation fields is set to k2π/(ω0−ωeff), where k has to be an integer, representing the number of full off‐resonance excitation/de‐excitation periods. The unintentional off‐resonance cyclotron excitation is shown to lead to an instrumental upper limit for the mass selectivity of ion selection, the so‐called front‐end resolution. This upper limit is proportional to the cell diameter, and the square of the magnetic field strength, and inversely proportional to the noise level of the excitation RF‐field, and the mass of the ions to be selected. It is demonstrated that an instrumentally dictated maximum mass resolution of better than 50000 can be obtained for the selection of ions with a nominal mass‐to‐charge ratio of 79.
Electron ionization mass spectrometry of phenylpyridazinylmethanols and phenylpyridazinyl ketones
Authors: Pittenauer Ernst , Allmaier Günter , Schmid Erich R. , Krenmayr Peter , Heinisch Gottfried , Budzikiewicz H.
Published: May 2005

The mass spectrometric fragmentation behaviour of four monosubstituted pyridazines (phenyl‐3‐ and phenyl‐4‐pyridazinylmethanol, phenyl‐3‐pyridazinyl and phenyl‐4‐pyridazinyl ketone) was investigated. Fragmentation pathways were established by combined interpretation of the data obtained from high resolution measurements and from low‐energy collision‐activated dissociation mass spectra of the molecular ions as well as of several important fragment ions. A clear differentiation between these 3‐ and 4‐substituted 1,2‐diazines is possible for both sets of pyridazines. Only the spectra of the 3‐isomers exhibit an abundant [MH]+ peak, which indicates a cyclization of these ions involving one ring nitrogen atom. Another difference between the two isomeric phenylpyridazinylmethanols is the loss of OH from the molecular ion, as detected for the C‐3 substituted compound only. For the phenylpyridazinyl ketones, the loss of CO from the molecular ion, which is only observed with the 3‐isomer, permits an unequivocal differentiation.
Fast‐atom bombardment mass spectrometry and metastable‐ion studies for the characterization of isomeric fluorosugars
Authors: Kiremire B. T. , Chirello D. , Traldi P. , Bravo P. , Resnati G.
Published: May 2005

Characterization of stereoisomeric 3,4‐dideoxy‐3‐fluoro‐hexoses has been carried out using fast‐atom bombard‐ment. Diagnostic fragments were observed in the daughter‐ion spectra of the [M‐H]− and [M+H]+ ionic species. Notable differences were also observed in the relataivae abundances of ionic species corresponding to [M‐H]−, [M‐H‐HF]− and [C11H11O2]− ions.
Use of a moving‐belt interface for on‐line high‐performance liquid chromatography/mass spectrometry characterization of polycyclic aromatic compounds of molecular weight up to 580 Da in environmental samples
Authors: Perreault H. , Ramaley L. , Sim P. G. , Benoit F. M. , Wise S. A.
Published: May 2005

The applicability of the moving belt high‐performance liquid chromatography/mass spectrometry (HPLC/MS) interface to the analysis of high molecular weight polycyclic aromatic compounds (PACs) in a complex sample derived from coaltar is investigated. This interface provides good preservation of chromatographic integrity and useful electron ioniation spectra of thermally stable PACs of low to moderate volatility up to molecular masses of at least 580 Da. It is concluded that this HPLC/MStechnique will be useful in the analysis of such complex samples, provided a large enoughsuite of standard compounds can be made available.
Anionic rearrangements of deprotonated α‐alkoxyvinyltrimethylsilanes in the gas phase
Authors: Eichinger Peter C. H. , Bowie John H.
Published: May 2005

α‐Alkoxyvinyltrimethylsilanes deprotonate to form two species −CHC(SiMe3)OR and CH2C(Si(Me)2CH2−)OR. The silylcarbanion undergoes the unusual rearrangement reaction CH2C(Si(Me3)2CH2−)OR → ((CH2CO)Me2RSiCH2−) Me2RSiCH2− + CH2CO. Loss of (R‐H) occurs when R ≥ Et; it is suggested that this is a reaction of the vinvl anion system.
Electrospray ionization mass spectra of hemoglobin and transferrin by a magnetic sector mass spectrometer. Comparison with theoretical isotopic distributions
Authors: Wada Yoshinao , Tamura Jun , Musselman Brian D. , Kassel Daniel B. , Sakurai Toru , Matsuo Takekiyo
Published: May 2005

Electrospray ionization mass spectra of human hemoglobin chains and of transferrin were acquired on a magnetic sector mass spectrometer. The observed molecular ion for each hemoglobin chain was in good agreement with the theoretical isotopic distribution at a reasonable resolution of 2000. The clear separation of a variant ß‐chain in admixture with the normal counterpart at mass 15867 that differed from it by 14 Da (0.09%) ensured that a smaller mass difference could be detected. The molecular ions for human transferrin were too broad compared with the theoretical shape to determine the molecular mass accurately, probably due to the heterogeneity of the carbohydrate moiety. A decrease in mass by neuraminidase digestion, however, determined the average number of sialic acids in the molecule.
Desorption of ions from locust tissues. II. Metabolites of E‐destruxin using negative‐ion fast‐atom bombardment mass spectrometry
Authors: Lange C. , Loutelier C. , Cherton J.‐C. , Cassier P. , Vey A. , Pais M.
Published: May 2005

Detoxification of E‐destruxin into E‐diol‐destruxin, conjugated glutathion‐E‐destruxin, cysteinyl‐E‐destruxin, and phosphorylated‐E‐destruxin in vivo in Locusta migratoria is demonstrated using direct negative‐ion fast‐atom bombardment mass spectrometry (FAB‐MS) without the need for prior extraction or purification.
The correct molecular weight of myoglobin, a common calibrant for mass spectrometry
Authors: Zaia Joseph , Annan Roland S. , Biemann Klaus
Published: May 2005

Myoglobins from horse heat muscle, horse skeletal muscle and sperm whale are widely used as calibration standards or test compounds for various mas spectrometric methodologies. In all such cases reproted in the literature, a molecular weight value is used (16950.5 and 17199, respectively) which is based on the assumption that amino acid 122 in this 153 amino‐acid‐long protein is asparagine, overlooking a published suggestion that it is aspartic acid instead. Since the mass assignment accuracy for matrix‐assisted laser desorption mass spectrometry is reproted to be ±0.01% and for electrospray ionization ±0.0025%, and error of one mass unit in ∼ 17000 would be significant. The mass‐to‐charge ration of ions of the tryptic peptide encompassing amino acid 122 derived from commercially available horse heart and horse skeletal myoglobins, the apomyoglobin of the latter, and the tryptic and chymotryptic peptide of sperm whale myoglobin proved that in both proteins amino acid 122 is indeed aspartic acid, rather than asparagine. This finding was further confirmed by the collision‐induced dissociation sectra of the [M+H]+ ions of the tryptic peptides from the horse myoglobins and the chymotriptic peptide from sperm whale myoglobin. Thus, the correct molecular weight of horse myoglobinis 16951.49 and that of the sperm whale protein is 17199.91.
Ionspray mass spectrometry of marine toxins. IV. Determination of diarrhetic shellfish poisoning toxins in mussel tissue by liquid chromatography/mass spectrometry
Authors: Pleasance Stephen , Quilliam Michael A. , Marr Julie C.
Published: May 2005

An Improved liquid chromatographic/mass spectrometric (LC/MS) method utilizing gradient elution and ion‐spray ionization is described for the sensitive determination of okadaic acid and dinophysistoxin‐1, the principal toxins implicated in cases of diarrhetic shellfish poisoning. The method was used to confirm the presence of both toxins, together with a recently identified isomer of okadaic acid, dinophysistoxin‐2, in various samples of cultivated blue mussels (Mytilus edulis) from Canadian and European Waters. The method provided a mass detection limit of 0.4 ng for each toxin, thus allowing detection of 40 ng per g of whole mussel tissue (or approximately 10 ng/g if only the digestive glands were used in the assay). Quantitative results obtained by LC/MS were in good agreement with those obtained by derivatization and high‐performance liquid chromatography with fluorescence detection.
Accurate mass measurement of proteins using electrospray ionization on a magnetic sector instrument
Authors: McEwen C. N. , Larsen R. S.
Published: May 2005

Peptides and proteins with molecular weights of ca 20 000 have been mass measured with accuracies of ±0.5 Da using electrospray ionization interfaced to a double‐focusing magnetic sector mass spectrometer. Factors affecting mass measurement accuracy such as resolution, peak profiles, calibration, data processing, and mass calculations are discussed.
Studies on the metabolism of omeprazole in the rat using liquid chromatography/ionspray mass spectrometry and the isotope cluster technique with [34S] omeprazole
Authors: Weidof Lars , Covey Thomas R.
Published: May 2005

This paper describes the application of the ionspray (pneumatically‐assisted electrospray) interface for liquid chromatography (LC) and atmospheric‐pressure ionization mass spectrometry (API MS) to samples obtained in a study on the metabolism of omeprazole. In this study [34S]omeprazole was utilized for the stable isotope cluster technique. Over forty metabolites in a sample of partially purified rat urine were resolved by gradient elution LC with ionspray API MS detection, and each of them produced molecular ion 1:1 clusters (MH+ and [MH+2]+). The Chromatographic fidelty of the total‐ion current (TIC) was excellent. The endogenous matrix of the sample was quite low, allowing a background‐substracted averaged mass spectrum of the entire TIC trace to produce a ‘metabolite mass profile’ depicting all the molecular ion 1:1 clusters in the sample. From this mass profile, it was possible to obtain direct information concerning oxygenation an conjugation reactions of the parent compound.
Sample immobilization protocols for matrix‐asssisted laser‐desorption mass spectrometry
Authors: Mock K. K. , Sutton C. W. , Cottrell J. S.
Published: May 2005

Methods are described fsor the purification of proteins prior to analusis by matrix‐assisted laser‐desorption mass spectrometry. Contaminated protein sample were immobilized onto the surface of sample targets and rinsed. In general, a layer of electrosprayed nitrocellulose gave better results than the sroughened gold surface of an untreated target. Using this approach, spectra could be obtained from low picomole quantities of protein in the presence of sdcontaminants which did not inhibit the binding of the protein to the substrate.
Synchronized collision‐cell energy ramping. Improving the quality of product‐ion spectra
Authors: Fitton E. M. , Monaghan J. J. , Morden W. E.
Published: May 2005

The design and use of an RF‐only collision‐cell ramp generator is described. The generatio controls the collision energy voltage applied to the RF‐only collision cell in a hybrid mass spectrometer of BEqQ geometry. The generator enables the collision‐cell voltage to be increased or decreased in a linear ramp, over the full 500 V available. The start/stop functions of the ramp are synchronized under data system control to the scan of the quadrupole mass analyser. The collision‐induced dissociation spectra so produced show an increase in the product ion abundance.
Mass spectrometric study of simple olefinic flames: Comparison with laser diagnostics of C2H4/O2/Ar flames at 20 torr
Authors: Howard Stephen L. , Locke Randy J. , Sausa Rosario C. , Miziolek Andrzej W.
Published: May 2005

A new research apparatus for characterization of low‐pressure premixed flames has been developed. This instrument incorporates several spectral techniques in one apparatus so that various diagnostic techniques can be quantitatively compared and the usable detection range expanded. Features include detection by mass analysis with a triple quadrupole mass spectrometer and by laser techniques such as laser‐induced fluorescence. Temperature profiles of the flame both with and without the mass spectrometer probe were obtained by thermocople. Concentration profiles of the highly reactive flame species H˙, O, and OH˙ were obtained and compared.
Analysis of a mass‐analyzed ion kinetic energy profile. II. Systematic determination of the kinetic energy release distribution
Authors: Yeh In Chul , Kim Myung Soo
Published: May 2005

A systematic method to evaluate the kinetic energy release distribution from the mass‐analyzed ion kinetic energy (MIKE) spectrum of a metastable ion decomposition, namely lunicolecular fragmentation of lpolyatomic ions, has been ceveloped. The analytical expression for a MIKE profile at a single kinetic energy release developed in lthe preceding paper has been utilized. The present method has been applied to the case of unimolicular dissociation of the t‐butylbenzene molecular ion and to the rather extreme case of a charge‐separation reaction of C7H generated form toluene. Excellent agreements between the experimental data and calculated results have been observed.
Exploratory data analysis applied to the interpretation of mass spectra of pyrrolidin‐1‐yloxy radicals
Authors: Jerkovich Gyula , Varmuza Kurt , Werther Wolfgang , Sár Cecília P. , Hideg Kálmán
Published: May 2005

Method of multivariate statistical analysis have been applied to the mass spectra of pyrrolidin‐1‐yloxy derivatives. A graphical representation of the results obtained by using fragment‐specific features proides a staightforward method of visualizing mass spectra/structure relationships. The explanatory power of the relatioonships can be assessed by finding linear discriminant components in the space of fragement‐type features. Computer‐generated spectral‐type features, when used as spectral classifiers, show statistilcally comparable performance on the same set of mass spectra.
Ion‐trap mass spectrometry applications in forensic sciences. I. Identification of morphine and cocaine in hair extracts of drug addicts
Authors: Curcuruto O. , Guidugli F. , Traldi P. , Sturaro A. , Tagliaro F. , Marigo M.
Published: May 2005

Daughter‐ion spectra obtained by ion‐trap mass spectrometry have been successfully employed in the field of drug abuse investigation. Selection and collison‐induced fragmentation of molecular‐ion species of morphine and cocaine lead to an easy identification of such molecules in hair extracts of heroin and cocaine addicts.
Comparison of the fast‐atom bombardment and electrospray ionization mass spectra of meso‐pyrzolylporphyrins
Authors: Aubagnac Jean‐Louis , Münster Helmut , Elguero José , Meutermans Wim
Published: May 2005

Fast‐atom bombardment (FAB) and Electrospray ionization (ESI) mass spectra of meso‐pyrazolylporphyrins have been studied. Both types of spectra allow one to determine the molecular weight of each compound studied. ESI mass Spectra show two further nteresting properties. First, there is addition of only one and two protons. Second, the ESI spectra show cluster ions for which the measured and theoretical isotope rations are in good occurrence of reduction phenomena prevents such a calculation from the FAB mass Spectra.
Mass spectral studies of some protoadamantanoid ketones
Authors: Škare Danko , Mlinarić‐Majerski Kata , Švob Valdimir , Milivojevič Dušan
Published: May 2005

The mass spectra of saturated and unsaturated protpadamentanoid ketones wee studied. Remarkable and unusual loss of water in 10 protoadamantanone is explaned by the flesibility of the ethono‐bridge and the ability for intera ction with carbony. three fragmentation paths of protoadamantanoid ketones are disussed.
Computer‐assisted determination of elemental composition of fragments in mass spectra
Authors: Kumar K. , Menon A. G. , Sastry P. S. , Mathur D.
Published: May 2005

This paper presents details of an expert system that infers elemental composition of fragment peaks in a mass spectrum and suggests possible chemical formulae for the molecular ion even when it does not itself appear in the spectrum. The system relies on a knowledge of the natural isotopic abundances of the elements, and exploits the fact that fragments are siblings, with the molecular ion as their parent. The program has been written in PASCAL and runs on any IBM PC‐AT compatible machine.
Electron‐impact induced fragmentation of spiro‐1‐pyrazolines
Authors: Dinya Zoltán , Lipták Miklós , Lévai Albert , Tóth Gábor , Vékey Károly
Published: May 2005

The positive‐ion electron impact mass spectra of twelve spiro‐1‐pyrazolines have been recorded as 70 eV electron energy and the dat analyzed to elucidate their fragmentation pathways. None of these compounds gave abundant molecular ions (M+) due to the instability of the pyrazoline ring. The first step in the decomposition of M+ ions is the elimination of a nitrogen molecule followed by a rearrangement resulting in the formation of the cation radical [M–28]+, the decomposition of which is discussed in detail. The proposed fragmentation pathways and their mechanisms are supported by high‐resolution data, linked‐scan measurements at constant B/E and collision‐induced dissociation‐mass‐analyzed ion kinetic energy spectra.
An electron ionization and fast‐atom bombardment mass spectrometric study of some N(10)‐substituted phenothiazine‐S‐oxides
Authors: Hegedüs‐Vajda Judit , Tamás József , Taulov Ivan G.
Published: May 2005

Electron ionization mass spectral behavior of N R substituted phenothiazine‐S‐oxides (R:CH2CCH3CH2, CH2CCH, CCCH3, COCH3, COC2H5 and COC6H5) has been studied by comparison of normal and daughter‐ion mass spectra. Among several characteristic pathways, formation of [MOR]+, C12H8NS+ ions (m/z 198) was found to result in a common and abundant fragment peak for both N‐alkyl and N‐acyl derivatives. Appearance energy measurements as well as thermochemical considerations revealed this ˙OR loss, to be a single‐step dissciation process and to correspond to the energetically most favoured primary decomposition of M+˙; it seems to involve a transannular rearrangement. The ˙OR elimination also occurred from [MH]+ ions, produced by fast‐atom bombardment.
An investigation of fragmentation mechanisms of doubly protonated tryptic peptides
Authors: Tang Xue‐Jun , Boyd Robert K. , Bertrand M. J.
Published: May 2005

Peptides formed as reaction products, of specific hydrolysis of proteins by trypsin, are characterized by a basic residue (Arg or Lys) as the C‐terminus, which facilitates formation of bundant [M+2H]2+ ions under electrospray r ionspry conditions. These doubly charged ions readily dissociate upon collisional activation to y" and b fragment ions which are mass complemens of one another. The suggestion tht these fragments are formed by direct charge‐separation disociatons must contend with the observation that the y" intensities are generaly appreciably larger than those of their b counterparts. However, it is shown that this can be accouned for by a greater susceptibility f the b ions to undergo further dissociaton to smaler fragments such as immonium ions. In addition no evidence could be found to support alternative mechanisms, including dissociative electron capture, for which equal intensities of the two fragment ion series are not obligatory. Initial protonation at the N‐terminus was shown to be required for formation of these [M+2H]2+ ions via its suppression by mono‐acetylation at the N‐terminus. These findings, and others concerning formation of [y"′]2+ fragments from singly protonated peptides, via charge‐site‐induced cleavages and intramolecular proto transfers between nitrogen atoms, respectively.
Characterization of iminopropadienone ions and neutrals in a tandem mass spectrometer
Authors: Flammang Robert , Laurent Sophie , Flammang‐Barbieux Monique , Wentrup Curt
Published: May 2005

Radical‐cations of iminopropadienones (RNCCCO+˙) have been generated by dissociative ionization of isoxazle precursors a structurally characterized by collisional activation mass spectrometry; the corresponding neutral cumulenes have also been produced in a tandem mass spectrometer by neutralization and/or flash‐vacuum pyrolysis experiments.
Kinetic energy measurements of molecular ions ejected into an electric field by matrix‐assisted laser desorption
Authors: Zhou J. , Ens W. , Standing K. G. , Verentchikov A. , Sundqvist B. U. R.
Published: May 2005

Measurements of kinetic energy distributions of molecular ions ejected into an extraction field by matrix‐assisted laser desorpton re reported. The measurements were made in a time‐of‐flight mass spectrmeter with an electrostatic mirror by measuring the reflected signal as a function of the difference between the accelerating voltage and the voltage applied t the mirror. The molecular ions ere found to have less kinetic energy than the extraction field alone would normally provide, i.e. we observed an nergy deficit. Under conditons typical for a matrix‐assisted laser desrptio experiment, the deficit is about 24 eV for oleclar ions of insulin. The size of the deficit increases with the intensity of the molecular ion signal, and the molecular weight of the protein; t is also larger for negative molecular ions than for positive molecular ions.
Mass spectrometric studies on some macrocyclic, macrobicyclic and macroacyclic Schiff bases
Authors: Guerriero P. , Tamburini S. , Vigato P. A. , Catinella S. , Traldi P.
Published: May 2005

The mass spectrometric behaviour of four macrocyclic, one macrobicyclic and one macroacyclic Schiff bases, obtained by one‐step multiple condensation reactions of 2,6‐diformyl‐4‐methylpropane, 1,3‐diamino‐ 2,2‐dimethylpropene, 1,5‐diamino‐3‐oxapentane or tris‐(2‐aminoethyl) amine under fast‐atom bombardment conditions, was studied in detail with the aid of mass‐analyzed ion kinetic energy spectrometry. The mass spectrometric behaviour of a mononuclear macrobicy La(III) complex is also described.
Investigation of the evaporation of graphite in high‐voltage vacuum discharge: The formation mechanism of carbon clusters
Authors: Cornides I. , Morvay L.
Published: May 2005

The applications of kinetics calculations to determine the size distribution of Cn clusters formed from the vaprized material of graphite requires aknowlledge of the initial composition of the carbon vapour. By a 13C iisotope tracer experiment it is shown that a considerable part of the Cn molecules in the case of n⩾3 evaporate directly as polyatomic fragments of the crystal structure of graphite, while the other, probably the greater part, is formed in the vapour. A more quantitative evalution of the experimental data is to be attempted later.
Application of fast‐atom bombardment mass spectrometry for sequencing of a hemoglobin fragment, naturally occuring in human cerebrospinal fluid
Authors: Glämsta Eva‐Lena , Nyberg Fred , Silberring Jerzy , Oliver R. W. A.
Published: May 2005

Recent studies have reveallled the presence of a new group of opioid peptides, the hemorphins, in the human pituitary as well as in human cerebrospinal fluid. The hemorphins are structurally related to sequence segments residing in the β, δ,γ or ϵ‐chains of hemoglobin. In this study we have applied fast‐atom bombardment mass spectrometry (FAB‐MS) to elucidate the sequence of a hemorphin fragment isolated from the cerebrospinal fluid of patients with cerebrovascular bleedings. The FAB‐MS was used in conjunction with carboxypeptidase Y degestion and results indicated that this procedure proved to be a powerful tool for rapid sequence determination. The recovered peptide was thus found to be identical with the sequence 32–41 of the above mentioned hemoglobin chainss.
Determination on the microscale of plasmatic lactic acid as its t‐butyldimethylsilyl derivative by stable‐isotope dilution using capillary gas chrommatography/mass spectrometry
Authors: Rocchiccioli F. , Sanière M.
Published: May 2005

A new sensitive and precise method for the determination of lactic acid in plasmatic microsamples (50 μL) has been developed. Lactic acid was directly extracted from plasma by ethyl acetate in acidic conditions, and analysed as its di‐t‐butyldimethylsilyl derivative by capillary gas chromatography/electron‐impact mass spectrometry (GC/MS). The internal pstandard was a previously synthesized deuterated compound, 3‐[2H]‐(2R)‐lactic acid. The method gives good reproductibility and precision, the ovedrall standard deviation being better than 3%. The GC/MS assay was in good agreement with the enzymatic determination.
Matrix‐assisted laser desorption of peptides and proteins on a quadrupole ion trap mass spectrometer
Authors: Jonscher Karen , Currie Graeme , McCormack Ashley L. , Yates John R.
Published: May 2005

The use of ultraviolet matrix‐assisted laser desorption (MALD) to ionize peptides for analysis in a quadrupole ion trap is described. An ion source was modified to accommodate a fiber optic to transmit laser radiation from a notrogen laser (337 nm) to the tip of the sample probe containing peptide of protein samples in a matrix of 2,5‐dihydroxybenzoic acid (DHB) or 3,4‐dimethoxy‐4‐hydrexy‐cinnamic acid. Detection limits are demonstrated with 10 fmol of sperm‐whale‐myoglobin. The dimer of sperm‐whale myoglobin was also observed at m/z 34, 430. A. comparison is made of the tandem mass spectrum of (MS/MS) of human angiotensin I desorbed by MALD to that of the peptide desorbed by liquid secondary‐ion mass spectrometry. Both spectra were found to contain abundant structural information.
Au+, Ag+ and Cu+ attachment to polybutadiene in laser desorption at 1064 nm
Authors: Dean Patricia A. , O'Malley Rebecca M.
Published: May 2005

Cu+, Ag+ and Au+ gas‐phase ions have been found, in laser desorption time‐of flight experiments, to attach efficiently to polybutadiene, a polymer containing no polar groups. The desorption and cation attachment were accomplished using the fundamental frequency of Nd:YAG laser, at a wavelength of 1064 nm, and supporting the samples on probe tips made of the appropriate metal. laser powers were in the range of 1.0–2.0 × 108 W/cm2. Time delays between the application of the laser pulse and the sampling of the resultant ion population were in the range 30–80 μs. The Au+ attachment is contrary to the reported findings from a laser desorption charge‐exchange spectrum obtained from a gold surface by Kahr and Wilkins. The differences in the spectra are discussed in terms of the differences in the two experimental methods. Attachment by these ions could be useful in the laser desorption analysis of other polymer molecules, particularly those containing no polar groups.