bluuebunny/crossref_metadata_2025 huggingface dataset:
Metastable decay of peptides and proteins in matrix‐assisted laser‐desorption mass spectrometry
Authors: Spengler Bernhard , Kirsch Dieter , Kaufmann Raimund , Cotter R. J.
Published: May 2005

Fragmentation of protein and peptide ions generated by matrix‐assisted laser desorption has been investigated using a modified LAMMA 1000 reflecting time‐of‐flight (TOF) mass spectrometer. Whereas fragmentation of covalent bonds prior to ion acceleration (i.e., within several ns after the laser pulse) in general is not observed using the matrix technique, extensive fragmentation on a longer time scale can be studied in our instrument. The high mass resolution (M/ΔM≈1200–1800 for insulin and peptides) permits the investigation of even small mass losses from parent molecular ions (occuring in the first section of the field‐free drift region) by measuring flight time differences of daughter ions acquired during passage through a two‐stage reflection. The kind and extent of this metastable decay has been found to depend strongly on the substance under investigation. Typical fragmentations are loss of ammonia and parts of the amino acid side‐chains. The large abundances of peaks due to such metastable fragmentation, observed for most of the peptides and proteins investigated, may, at least in part, explain peak broadening (and, hence, poor mass resolution) typical in matrix‐assisted laser‐desorption TOF mass spectra.
Factors affecting the ionization efficiency of quaternary ammonium compounds in electrospray/ionspray mass spectrometry
Authors: Raffaelli Andrea , Bruins Andries P.
Published: May 2005

A series of quaternary ammonium salts was analysed by the ionspray technique under different conditions in order to study the influence of some important factors on the ionization efficiency, The factors taken into account were droplet charging, sample ion, counter ion, solovent composition, and concentration. Measurement of the spray current leaving the nebulizer has shown that the spray current increases linearly with sample concentration up to at least 50 pmol/μL. The measured spray current is approximately 30% of the calcualated current corresponding to a given concentration of quaternary ammonium ions in solution leaving the nebulizer at a given flow rate. The results obtained show that tetraakylammonium salt give the best sensitivitly with no influence of sample‐ion shape or counter ion. The dynamic range for full‐scan mass spectra of the compounds studied appears to the linear for concentrations from 0.1 pmol/μL (10−7M) up to 10 pmol/μL (10−5M).
An A priori relationship between the average and monoisotopic masses of peptides and oligonucleotides
Authors: Zubarev R. A. , Bonddarenko P. V.
Published: May 2005

A straightforward relationship between the average and the monoisotopic masses of peptides (proteins) and oligonucleotides is proposed which allows one to calculate the monoisotopic mass from aknown average mass with a 0.1 u order of precision. The approach offered here can be applied to any type of biopolymer.
Molecular weight determination of recombinant interleukin 2 and interferon gamma by electrospray ionization mass spectroscopy
Authors: Maquin Francis , Schoot Bernard M. , Devaux Philippe G. , Green Brian N.
Published: May 2005

The molecular weights of the recombinant proteins interleukin 2 and interferon gamma were determined by electrospray ionization (ESI) mass spectroscopy on the whole molecules. For interleukin 2 an average experimental mass of 15 549.4 u, was observed in excellent agreement with the theoretical average mass of 15 547.2 u. The mass observed for interferon gamma (16 908.4 u) agreed with the theoretical molecular weight of the monomeric species (16 907.3 u). By ESI mass spectrometry it was possible to determine the presence of proteins lacking one or two amino acids.
Electrospray ionization for analysis of platelet‐activating factor
Authors: Weintraub Susan T. , Pinckard R. Neal , Hail Mark , Gaskell S. J.
Published: May 2005

Platelet‐activating factor (PAF) was analyzed by electrospray‐ionization spectrometry (ESI‐MS) using a single quadrupole mass spectrometer. The positive‐ion spectrum was dominated by an ion corresponding to a sodiated molecule when a low potential difference between the capillary exit (nozzle) and the skimmer was employed, but when the capillary exit voltage was increased, fragmentation of PAF was observed. Initial fragmentation involved the loss of the elements of trimethylamine from the sodiated molecule to yield [M+Na−59]+. An intense ion at m/z 147, generated by the loss of trimethylamine from the sodiated phosphocholine portion of the molecule was also detected, along with a lower intensity ion at m/z 184 which is representative of a protonated phosphocholine moiety. With negative‐ion detection the major molecular species was [M + Cl]−. Interpretation of the mass spectral fragments was verified by ESI tandem mass spectrometry on a triple‐quadrupole tandem mass spectrometer.
Gas‐phase chemistry of metal oxide anions. The reactions of dioxomanganate(III), MnO and trioxomanganate(V), MnO ions with aliphatic alcohols
Authors: Fokkens R. H. , Gregor I. K. , Nibbering N. M. M.
Published: May 2005

Results of gas‐phase reactions of MnO and MnO ions with a series of aliphatic C1C4 alcohols show that C2C4 primary alcohols are oxidized by MnO in reaction channels which involve proton abstraction and hydride‐ion transfer, along with the appearance of [H.Mn.O.OH]− ions. Secondary alcohols are oxidized in slower processes while menthanol and t‐butanol are unreactive. MnO/alcohol reactions are more complex and involve the formation of [H.MnO3]−, [H.Mn.O2.OH]−, [RO.Mn.O.OH]−, [(RO)2 Mn.O]− and the terminal solvated ion [(RO)3.Mn.OH]−.
Matrix‐assisted laser desorption ionization with a magnetic mass spectrometer
Authors: Hill James A. , Annan Roland S. , Biemann Klaus
Published: May 2005

Matrix‐assisted laser desorption ionization has been carried out with a high mass double‐focusing magnetic mass spectrometer. The pulsed ion signal, generated by irradiation of the sample (substance P, ubiquitin, and cytochrome c) embedded in 2,5‐dihydroxybezoic acid with a XeF excimer laser (353 nm, 12 ns pulse, 10–160 Hz), was recorded with an integrating array detector. Good resolution of 2600 (full width at half maximum) and high sensitivity (a few pmol) were obtained. The loss of small neutral fragments was observed, supporting the notion that the peak broadening observed in the time‐of flight mass spectrometers commonly used for this ionization mode is due to such metastable decomposition.
Isomerization reaction of [C6H6 C4H] π complexes
Authors: Berthomieu Dorothée , Audier Henri‐Edouard , Monteiro Candida , Denhez Jean‐Pierre , Maquestiau A.
Published: May 2005

Metastable protonated butylbenzenes have been studied by extensive labelling and kinetic energy release measurements. Protonated s‐butylbenzene isomerizes by 1–2 hydrogen shift to the π complex [C6H6 SC4H], and the SC4H cation rearranges to t‐C4H. The interconversion between [C6H6 SC4H] and [C6H C4H8] ion/neutral complexes is demonstrated. Protonated t‐butylbenzene reacts without hydrogen exchange to give t‐C4H, while protonated n‐butylbenzene isomerizes to s‐butylbenzene prior to dissociation. Protonated iso‐butylbenzene isomerizes to protonated t‐butylbenzene and to protonated s‐butylbenzene. In the 2nd field‐free region, the dissociation of this last form predominates.
Mass spectrometry of nuphar alkaloids
Authors: Bortolini Olga , Curcuruto Orenella , Traldi Pietro , Wróbel Jerzy T. , Vékey Kàroly
Published: May 2005

This paper summarizes the data obtained during the last 20 years on the mass spectrometric behaviour of C15 and thio−C30 nuphar alkaloids. The usefulness of this technique in the solution of stereochemical problems is confirmed.
Structure determination of the antibiotic desertomycin B by fast‐atom bombardment mass spectrometric techniques
Authors: Dinya Zoltán , Sztaricskai Ferenc , Horváth Géza , Vékey Kàroly
Published: May 2005

By means of different fast‐atom bombardment (FAB) mass spectrometric techniques (i.e., positive‐ and negative‐ion FAB ionizations and high resolution measurements) we have determined the chemical structure of desertomycin B which is a novel representative of the family of macrolide antibiotics carrying a guanidino function in its side‐chain.
Laser‐pulse ejection of organic molecules from a matrix: Lessons from fast‐ion‐induced ejection
Authors: Johnson R. E. , Sundqvist B. U. R. , Ens W.
Published: May 2005

Lessons learned from electronic sputtering by incident ions of condensed‐gas solids and solids composed of biomolecules are applied to laser‐pulse‐induced ejection of biomolecules inbedded in a matrix of small molecules. In electronic sputtering by fast ions, single excitation desorption, thermally activated sputtering, and pressure‐pulse sputtering have been observed. In addition, yields for ejected ions have been shown to exhibit trends different from yields for ejected neutrals. The parallel processes are considered for laser‐pulse ejection of a martix with imbedded molecules and expressions are given to examine the yield data.
Thermally induced dissociation of ions from electrospray mass spectrometry
Authors: Rockwood Alan L. , Busman Mark , Udseth Harold R. , Smith Richard D.
Published: May 2005

The thermally induced dissociation (TID) of inos at near atmospheric pressure, followed by their mass spectraometric analysis, is demonstrated. The TID occurs in a heated metal capillary interface, and should be broadly applicable to any system capable of producing ions at high pressure. The heated capillary provides a reaction vessel, potentially very useful for kinetic and mechanistic studies of ions. The technique has been applied to the fragmentation of large multiply charged ions from an electrospray ionization source. Preliminary results show that stability for multiply protonated petide or protein molecules in inversely related to its charge.
Ion counting and ion intensity measurements in time‐of‐flight mass spectrometry. Application to matrix‐assisted laser desorption
Authors: Baptista G. B. , Brunelle A. , Chaurand P. , Della‐negra S. , Depauw J. , Le Bayec Y. , Chait B. T.
Published: May 2005

A time‐to‐digital converter coupled to a charge‐to‐digitalconverter has been used to record mass spectra in matrix‐assisted laser desorption(MALD) time‐of‐flight mass spectrometry. Masses above 100 000 Da have been detected by ion counting. Utilizing an electrostatic mirror, good mass resolution has been achieved in MALD. When the number of detedted secondary ions is small the sensitivity of mass measurements is improved by using a charge‐to‐digital converter rather than a transient recorder.
Mass spectrometric analysis of a transition‐metal‐binding peptide using matrix‐assisted leaser‐desorption time‐of‐flight mass spectrometry. A demonstration of probe tip chemistry
Authors: Nelson Randall W. , Hutchens T. William
Published: May 2005

Matrix‐assisted laser desorption time‐of flight mass spectrometry has been used to investigate the affinity of aqueous copper ions for a 26‐residue synthetic peptide predicted to have metal‐binding properties. A specific reaction occurred upon the dirct application of aqueous CuSO4 to the matrix/peptide sample remaining on the probe tip ater initial mass spectrometric investigation. Results indicated the binding of up to one copper ion per histidine residue and the loss of one proton for each bound copper. Bound copper was not returned to solution upon subsequent cold water washings of the probe tip. These results suggest that covalent interations, between the copper and the peptide, occurred during the probe‐tip application of the metal ion to the sample.
Negative‐ion fragmentations of deprotonated heterocycles. The pyrazole and imidazole ring systems
Authors: Adams Gregory W. , Bowie John H. , Hayes Roger N.
Published: May 2005

Imidazole and pyrazole deprotonate preferentially at the 1‐position, and a number of fragmentations are best rationalized as occurring through common ring‐opened intermediate −NHCHCHCN. C‐Methylomidazoles and pyrazoles fragment similarly.
Mass spectrometer sysrtems and products. An expanded directory of manufacturers and suppliers
Authors: Lammert S. A. , Cooks R. G.
Published: May 2005

A directory of companies which supply mass spectrometers, components and services is provided. This directory expands on an earlier version.
Development of a condensation technique for thin‐layer chromatography/fast‐atom bombardment mass spectrometry of non‐visible compounds
Authors: Oka Hisao , Ikai Yoshitomo , Kondo Fumio , Kawamura Norihisa , Hayakawa Junko , Masuda Katsuyoshi , Harada Ken‐Ichi , Suzuki Makoto
Published: May 2005

In Order to prevent the diffusion of sample when a matrix is deposited on the sample spot on a thin‐layer chromatography (TLC) plate and to obtain constructively high sensitivity in mass spectrometry, we developed a conedensation technique including ‘trapezoid technique’ for TLC/fast‐atom bombardment mass spectrometry (FABMS) on both silica gel and C18 plates. For colored samples and colorless samples having a chromophore, the condensation technique previously in use, that condenses the sample towards the center of the spot in a line, using methoanol, was effective. The trapezoid condensation technique has been newly developed for colorless compounds having no chromophore. The mass spectra obtained using this technique clerly showed molecular ion species at relatively lower concentrations of samples, and the technoique can improve the detection limits of molecular ion species in TLC/FABMS by 3‐100 times with good reproducibility.
Secondary‐ion generation from large keV molecular primary ions incident on a stainless‐steel dynode
Authors: Kaufmann Raimund , Kirsch Dieter , Rood Hans‐Achim , Spengler Bernhard
Published: May 2005

Positive and negative secondary ions from large (up to 40 KDa) peptide and protein primary ions incident at 5–40 keV collisional energies on a stainless‐steel (mesh) conversion dynode have been investigated in a tandem (reflectron) time‐of‐flight arrangement. Negative secondary‐ion spectra consisted mainly of H− and C2H−, C2H ions; positive secondary‐ion spectra were more complex and contained prominent signals due to H+, Na+ and K+, and further signals at m/z. 28, 41, 43, 45, 73 up to m/z 326. The secondary mass spectra were qualitatively very similar amongst the various peptide primaries and not different from those of other organic projectiles such as, for example, coronene or cyclodextrin. With increasing mass of the primary ion, ratios of the secondary‐ion abundances changed drastically in the negative secondary‐ion spectra (increase of higher m/z signals, decrease of H−). Since most of the positive secondary ions could be attributed to a silicon‐organic surface contamination of the dynode (vacuum grease), it is concluded that the formation of such secondary ions is due to sputtering rather than surface‐induced dissociation.
Triphosphorus disulfide: The elusive P3S radical generated and identified by neutralization/reionization mass spectrometry
Authors: Keck Helmut , Kuchen Wilhelm , Tommes Peter , Wong Thomas , Terlouw Johan K.
Published: May 2005

The dissociative ionization by electron impact (70 eV) of terraphosphorus trisulfide, P4S3, yields P3S ions whose neutralization/reionization mass spectrum shows that the elusive P3S radical is a viable species in the rarefied gas phase. Ab initio molecular orbital calculations indicate that the structure of this radical is that of a planar five‐membered PPSPS ring of C2v symmetry.
Negative‐ion fast‐atom bombardment mass spectra of fluorosilicates. Reactivity of matrices
Authors: Aubagnac Jean‐Louis , Poirier Monique
Published: May 2005

Negative‐ion fast‐atom bombardment mass spectra of fluorosilicates allow their identification. Both a glycerol matrix and a m‐nitrobenzyl alcohol matrix show specific reactivities towards the anions.
Gas‐phase chemistry of first transition series carbonyl metallate ions, [Metal(CO)x]−: Reactions with 13C‐ and 18O‐Labelled carbon dioxide. A Fourier‐transform ion cyclotron resonance study
Authors: Gregor I. K. , Gregor R. C.
Published: May 2005

Gas‐phase reactions between 13CO2 and C18O2 and a series of carbonyl metallate ions [Metal(CO)x]− with x=3, 4 for the metals chromium, manganese, iron and also x=2 for iron, have ben examined at low pressures by Fourier‐transform ion cyclotron resonance mass spectrometry. while the 16‐and 17‐electron ions [Mn(CO)4]− and [Fe(CO)4]− were unreactive, both ligand displacement and oxidative reactions have been identified for the other 13‐, 14‐ and 15‐electron metal‐ion systems as a consequences of Metal‐C, O13 and 18OC cleavages in [(CO)x. Metal. η2‐OCO]− intermidiates.
Electron impact and chemical ionization mass spectrometry of heterocumulenes produced by flash vacuum pyrolysis
Authors: Brown Jeff , Flammang Robert , Govaert Yasmine , Plisniedr Michel , Wentrup Curt , Van Haverbeke Yves
Published: May 2005

Heterocumulenes such as ketenes, propadienones and comulogs of isocyanates are produced by flash vacuum pyrolysis of Meldrum's acid. Real‐time monitoring of the pyrolysis products is performed by methods of tandem mass spectrometry. In particular, chemical ionization is show, for the first time, to generate protonated moleculular ions of these kinetically unstable neutral molecules which can be identified by collisional activation experiments.
Detection of nitrotoluene isomers by ion cyclotron resonance mass spectrometry using ion/molecule reactions with NO+ as reagent
Authors: Xu Guoying , Herman Jan A. , Harrison A. G.
Published: May 2005

Ion/molecule reactions in nitrotoluene/NO and nitroluene/OCS systems were studied in an ion cyclotron resonance mass spectrometer. The formation of an adduct ion between m‐nitrotoluene and NO (or OCS to a lesser extent) differentiates it from the o‐ and p‐nitrotoluene isomers can be distinguished by their different decomposition rates into C7H6NO+ and C7H6NO+ fragment ions.
Doubly ionized states of CH4 studied by double‐charge‐transfer and auger‐electron spectroscopies
Authors: Griffiths W. J. , Svensson S. , Naves de Brito A. , Correia N. , Langford M. L. , Harris F. M.
Published: May 2005

High‐resolution double‐charge‐transfer spectroscopy has been used to measure the double‐electron‐capture reactions with CH4. Using kilo electron volt OH+, CI+ and F+ projectile ions it is possible in double‐electron‐capture reactions with CH4 molecules to populate the ground triplet state of CH. The energy of this state relative to the gound state of CH4 is found to be 38.2±0.4 eV, while the fiest excited triplet state is found at a double‐ionization energy of 46.7±0.8 eV. In double‐electron‐capture reactions involving H+ projectile ions and CK4 molecules, low‐lying singlet states of CH are populated. The energies of the four lowest singlet states in CH were measured to be 39.2±0.4, 40.5±0.4, 42.1±1 and 51.0±1 eV. High‐resolution photon‐induced Auger‐electron spectra of the CH4 molecule have been recorded. The KLL Auger Spectrum shows four distinct structures in the 30–70 eV double‐ionization evergy range centred at 40.3±0.1, 47.03, 53.2±0.3 and 6.9±0.3 eV. The previously published data on CH have been reviewed.
How are ions formed from electrosprayed charged liquid droplets?
Authors: Hiraoka Kenzo
Published: May 2005

The dependence of ion intensities on capillary position has been investigated for electrosprayed solutions of 5 × 10−6M (CH3)4 NBr and 10−3M CH3COOH in CH3OH+H2O+CCI4. It was found that the efficiencies for desorption from the charged liquid droplets into the gas phase are in thE order (CH3)>NH>CH3OH. The intensities of ions with higher desorption efficiencies become strong near the periphery of the spray cone, whereas those with lower desorption efficiencies have maxima in the central region of the spray cone. With increase of the vertical distance between the capillary tip and the sampling orifice, the distribution of the space‐charge density becomes nearly uniform in the spray cone due to the space‐charge field.
Probing vibrational modes in a neutral triatomic molecule by high‐resolution translational‐energy spectrometry
Authors: Mathur D. , Wilkins A. C. R. , Brenton A. G.
Published: May 2005

High‐resolution translational‐energy spectrometry has been applied to study vibrational excitation in neutral CO2 in its ground electronic state by 3 ke V impact by O+, N+, Ne+, Ar+ and Xe+ projectile ions. Three quanta of asymmetric stretch mode are excited. Bending mode vibrational excitation also manifests itself in translational‐energy spectra obtained with the heavier projectile ions (Ne+, Ar+ and Xe+). In the case of the O+ projectiles, simultaneous electronic (O+,2D⇔︁2P) and vibrational (CO2, ν3=0→1) excitation is also observed.
Improved accuracy of mass measurement with a quadrupole ion‐trap mass spectrometer
Authors: Williams Jon D. , Cooks R. Graham
Published: May 2005

Mass Measurement accuracy of better than 0.015% on protonated gramicidin S (nominal chemical average molecular weight 1141.5 Da) and its first three isotopes has been achieved using reasonant ion ejection in the quadrupole ion‐trap mass spectrometer operated at unit resolution. Analyte and Calibrant ions are subjected to identical injection and trapping conditions when desorbed by Cs+ ions from a split prone‐tip and co‐injected into the trap. When the mass analysis scan rate is slowed, enhanced resolution is achieved for all ions but the mass range accessed in a single scan of the digital‐to‐analog converter, which controls the mass analysis scan, is limited making calibration difficult. A peak‐matching procedure is described for use at these higher resolution conditions in which the offset voltage which determines the origin of the RF amplitude ramp is adjusted in such a fashion that the analyte and calibrant ions occur at the same point in the mass analysis scan. This procedure gave an improved mass measurement accuracy of better than 0.007% for the protonated gramicidin S. ions.
On‐line isotachophoretic analyte focusing for improvement of detection limits in capillary electrophoresis/electrospray mass spectrometry
Authors: Tinke A. P. , Reinhoud N. J. , Niessen W. M. A. , Tjaden U. R. , van der Greef J.
Published: May 2005

Detectability enhancement in capillary electrophoresis/mass spectrometry (CE/MS) has been realized using on‐line isotachophoretic (ITP) analyte focusing. This is demonstrated for the analysis of a mixture of anthracyclines, showing on at least 200‐fold improvement detectable concentration for ITP/CE/MS compared to CE/MS using an electrospray (ESP) interface.
Unequivocal discrimination between consecutive and competing collisionally induced decompositions in an ion trap
Authors: Paradisi Cristina , Todd John F. J. , Traldi Pietro , Vettori Umberto
Published: May 2005

Discrimination between consecutive and competing collisionally induced decomposition (CID) reactions can easily be obtained by a new pocedure consisting of the collisional activation of a parent ion and the simultaneous ejection of one of its daughter ions in an ion trap. This is done by applying, during a single storage phase, a DC voltage appropriate to induce fragmentation (‘boundary’ activation) of the parent and, at the same time, a ‘tickling’ RF potential, sufficient to eject a selected daughter ion rapidly from the trap. Several examples are reported which illustrate the capabilities of the procedure in establishing fragmentation pathways e.g., to determine whether a daughter ion is formed in a stepwise process involving an intermediate primary fragment rather than from the direct fragmentation of the parent ion. Salient features of this technique are discussed.
Analysis of pesticides using liquid chromatography/atmospheric‐pressure chemical ionization mass spectrometry
Authors: Doerge Daniel R. , Bajic Steve , Millington D. S.
Published: May 2005

Seventeen pesticides in five chemical classes (triazines, phenylureas, carbamates, organophosphates, miscellaneous) from the US Environmental Protection Agency's National Pesticide Survey of groundwater contaminants were selected for analysis by atmospheric pressure chemical ionization (APCI‐MS). The spectra obtained from most compounds consisted solely of [M + H]+ in positive‐ion mode. One example, p‐nitrophenol produced only the [M − H]− ion in negative‐ion mode. Increasing the potential on the sampling cone effected voltage‐dependent fragmentation of all carbamates ad alachlor to form diagnostic daughter ions. Detection limits (Limit of detection (LOD), signal‐o‐noise ratio=3) in full‐scan or selected‐ion monitoring mode varied from 0.8–10 ng of 0.01‐1 ng, respectively, and calibration curves were highly linear from the LOD to 100 ng. Mobile phase composition (50–100% acetonitrile in water) and flow rate (0.24 and 1.25 mL/min) had small effects on sensitivity of response. These reslts suggest that the sensitivity of APCI‐MS is affected less than that for thermospray and particle beam LC/MS by chemical differences in analyte structure for the pesticide classes tested. The low detection limits, high degree of linearity, the ability t produce diagnostic fragment ions using cone voltage fragmentation and the inter‐class versatlity suggest that APCI is a valuable technique for multiresidue confrmations of pesticides in groundwater.
Ion detection limitations to mass resolution in matrix‐assisted laser desorption time‐of‐flight mass spectrometry
Authors: Brown R. S. , Gilfrich N. L.
Published: May 2005

The ion detection process in a discrete‐dynode electron multiplier can result in significant mass resolution losses in time‐of‐flight mass spectrometry (TOF‐MS) for higher mass‐to‐charge (m/z) ion species. This resolution loss is attributed to propagation time delays and signal broadening in the ion detector. This is presumed tobe due to the generation o a distribution of secondary ion species produced initially upon impact of a primary ion with the first ynoe surface of the ion detector. Comparisons are made between the signals produced by a standard discrete dynode ion detector (which amplified the negatively chqrged species produced by impact of a primry ion) and a detector modified to respond to only the positively charged secondary ion species produced by a primary ion impact. Ion signals for higher m/z ions with the standard detector geometry are see to be due to a narrow signal component, most likely due to the generation o secondary electrons and/or very low mass secondary ions (H−), and a broad signal component, apparently due to secondary ions which take signifiant amounts of time to traverse the low potential fields between the first and second detector dynode. This results in ion signal tailing for higher m/z ion species. Numerical subtraction of the ion signal obtained with the standard and modified detector geometries (singly protonated molecular ion species of equine myoglobin) results in an improvement in mass resolution, such that a new adduct ion species (from trifluoroacetic acid) can be resolved.
Thermally assisted electrospray interface for liquid chromatography/mass spectrometry
Authors: Lee Edgar D. , Henion Jack D.
Published: May 2005

An electrospray interface for liquid chromatography/mass spectrometry (LC/MS) is described that combines the direct heating of High‐performance liquid chromatography (HPLC) effluent that is characteristic of thermoooospray‐type interfaces. This interface is called the thermally assisted electrospray interface for LC/MS. The device can accept the total effluent from a liquid chromatograph at flow rates ranging up to 500 μL/min. The HPLC effluent is nebulized into charged droplets by a combination of heat and an applied electric field. Ions emitted from charged droplets are mass‐analyzed by a triple quadraupole mass spectrometer equipped with an atmospheric pressure ion sampling orifice. Singly or multiply charged ions, indicating the molecular weight of a sample, are observed with minimal fragmentation. The extent of multiple charging observed in electrospray and ion spray mass spectrometry is decreased somewhat in thermally assisted electrospray. Labile compounds which undergo thermal decomposition by conventional thermospray show no decomposition with thermally assisted electrospray.
A novel derivatization method for peptides to increase sensitivity and backbone fragmentation in liquid secondary‐ion mass spectra
Authors: Kiplinger Jeffrey P. , Contillo Leonard , Hendrick W. Lee , Grodski Alex
Published: May 2005

Derivatization is used to increase both negative‐ion sensitivity and positive‐ion sequence information in the liquid secondary‐ion mass spectra (LSIMS) of a series of peptides. The derivatization method involves acylation with pentafluorobenzyl fluoride in a single‐step reaction, and the reaction mixture is applied directly to the probe tip for analysis. Acylation takes place at the unprotexted N‐terminus, tyrosine, and lysine. The derivatives exhibit increased signal‐to‐noise ration for [MH]− ions, especially where there is not already an acidic amino acid residue in the peptide. In positive‐ion LSIMS, the N‐terminal group acts to retain the charge at the N‐terminus, simplifying the fragmentation by producing N‐terminal fragment ions. It also increases positive‐ion fragmentation, sometimes very dramatically, making sequence determination more straightforward. The simplicity of the process, together with the enhancements it provides, make3 this a generally useful method for obtaining peptide structural information.
An investigation into the electron‐ionization‐induced mass spectrometric behaviour of some trans‐ and cis‐substituted cycloalkylamines of pharmaceutical interest
Authors: Anchisi Carlo , Fadda Anna Maria , Maccioni Anna Maria , Maccioni Elias , Favretto Donata , Traldi Pietro
Published: May 2005

The electron‐ionization‐induced mass spectrometric behaviour of eight cyclopentylamine and cyclohexylamine derivatives, recently synthesized, has been investigated by means of accurate mass measurements and metastable ion studies. These approaches allowed an easy structural characterization of the title compounds. In particular, mass‐analyzed ion kinetic energy spectroscopy proved effective for the differentiation of cis‐ vs trans‐isomers.
Improved methodology for liquid chromatography/continuous flow secondary‐ion mass spectrometry: Quantitation of abscisic acid glucose ester using reaction monitoring
Authors: Hogge Lawrence R. , Balsevich John J. , Olson Douglas J. H. , Abrams Garth D. , Jacques Suzanne L.
Published: May 2005

Improvements in methodology for liquid chromatography/continuous flow secondary‐ion mass spectrometry (LC/CFSIMS) are described. Practical procedures have been developed for the preperation of packed fusedsilica capillary liquid chromatography columns and the coupling of these columns to the CFSIMS probe. A modified probe tip is described that significantly reduced ion beam instability arising from acceleration voltage discharge, changes in mobile phase composition during gradient elution, and uneven tip wettability. Interfering matrix background ions in LC/CFSIMS experiments are eliminated by reaction monitoring: the detection limit of the plant hormone metabolite, abscisic acid glucose ester, ABAGE is below 100 pg (235 fmol) with this technique. Reproducibility for quantitation is achieved by parallel reaction monitoring of the analyte and an added internal standard, ABAGE‐d6. The d6/d0 ABAGE response ratio for the monitored transitions is linear over the range 100 pg to 10 ng of injected ABAGE.
Matrix‐assisted laser desorption mass spectrometry of cytochromes P450
Authors: Lewis Sydell , Korsmeyer Katy Kuo , Correia Maria Almira
Published: May 2005

Matrix‐assisted laser desorption ionization on a time‐of‐flight (MALDI/TOF) mass spectrometer provides a rapid and accurate method for molecular weight determination of hydrophobic cytochrome P450 proteins (P450s). A mass accuracy of 0.075% was achieved by analysis of dialyzed P450 2B1 using bovine serum albumin (BSA) as an internal standard. The measured mass of cytochorme P450 2B2 with MALDI/TOF resulted in an average molecular weight which was higher than reported values. Immobilization procedures proved extremely effective on samples containing high concentrations of phosphate buffers.
The use of hydrogen‐deuterium exchange to facilitate peptide sequencing by electrospray tandem mass spectrometry
Authors: Sepetov Nikolai F. , Issakova Olga L. , Lebl Michal , Swiderek Kristine , Stahl Doughas C. , Lee Terry D.
Published: May 2005

The utility of hydrogen‐deuterium exchange for sequencing peptides by mass spectrometry is demonstrated. The number of exchangeable hydrogens in a peptide is readily obtained by electrospray analysis of the peptide dissolved in deuterated solvents. This information can be used, in conjunction with published computer algorithms for interpreting peptide mass spectra, to reduce significantly the number of candidate sequences that fit the experimentsl data. This information, when combined with fragment‐ion information in the mass spectrum, greatly increases the reliability of sequence determination.
Stereospecific Retro‐Diels‐Alder reactions in the negative‐ion mass spectra of Diels‐Alder adducts of substituted p‐benzoquinones and glucofuranodienes
Authors: Madhusudanan K. P. , Dhami T. S. , Rani A. , Suryawanshi S. N.
Published: May 2005

The negative ions of cis‐ and trans‐Diels‐Alder adducts of p‐benzoquinones and glucofuranodienes enable these stereoisomers to be differentiated because the cis‐ isomers undergo a highly‐favoured retro‐Diels‐Alder reaction.
Vaporization processes of borosilicate coatings studied by high temperature mass spectrometry and using an induction plasma generator
Authors: Stolyarova V. L. , Archakov I. Yu. , Gordeev A. N. , Yakushin M. I. , Shultz M. M.
Published: May 2005

A new approach has been applied to study processes which take place during the thermochemical action of air (or other) plasma on heat protection materials. Vaporization processes of the borosilicate coating of ‘Buran's’ heatprotective tiles, both the initial state and after rf‐entry simulation testing (up to 100 landings), were investigated by the Knudsen mass spectrometric effusion method. Modelling of the thermochemical action of the shock‐layer plasma onto the front surfaces of real‐scale tiles was carried out by using an induction plasma genetor of 500kW power. It was established that the thermochemical action of the plasma causes, essentially, a decrease of vapour pressure over the coating. However, despite this decrease, the pressures observed are significantly higher than those over the SiO2–B2O3 system at the same temperature, due to gas‐phase SiO production by reaction between boron and silicon oxides and SiB4, which are contanied in the coating. The data available aiiow one to postulate the presence of the SiBO molecule in the gas phase. Data on mass‐loss rates obtained by direct measurments after re‐entry simulation compared nwell with the values calcuted from mass spectrometric data. It is suggested that the difference observed is caused by thermochemical action of atomic oxygen on the coating.
Structural investigation of the hydroxy‐propynal molecular ion
Authors: Pandolfo L. , Paiaro G. , Somogyi Á. , Catinella S. , Traldi P.
Published: May 2005

A formyl ketenyl platinum derivative, trans‐μ1‐(PCy3)2(H)Pt[C(CHO)CO] (where Cy represents a cyclohexyl group), when reacted with HCl, gives a C3H2O2 species among the reaction products. The structure was investigated mass spectrometrically by study of the reactions of metastable ions, and the information gained was combined with data from theoretical calculations to rationalize the structure of the C3H2O2 molecule.
An ion‐trap mass spectrometric study on electron impact and collisionally induced decomposition pathways of some phenothiazine S‐oxides
Authors: Guidugli F. , Curcuruto O. , Traldi P. , Hegedus‐Vajda J. , Tamas J. , Taulov I. G.
Published: May 2005

The electron ionization (EI) mass spectra and the daughter‐ion spectra of the EI‐generated main fragments of phenothiazine S‐oxides and its two N‐substituted derivatives have been studied by means of ion‐trap mass spectrometry (ITMS). Interesting differences with the data already published on the same molecules as obtained by a magnetic sector instrument have been rationalized by considering how, under ITMS conditions, charge exchange or self‐chemical‐ionization phenomena can take place, leading to molecular species with low energy content.
Mass spectrometric studies of some new hafnocene dialcoholates
Authors: Grafov Andrèi V. , Favretto Donata , Traldi Pietro , Battiston Giovanni A. , Porchia Marina , Rossetto Gilberto , Zanella Pierino
Published: May 2005

The electron ionization mass spectrometric behaviour of a new class of hafnocene dialcoholates, and, for comparison, of hafnocene dichloride, is discussed. They are also compared on the basis of mass‐analysed ion kinetic energy spectrometry. Fragmentation patterns of oxygen‐containing species give relevant information on their potential as precursors for the deposition of HfO2 thin films via metal‐organic chemical vapour deposition.
Randomization in the fragmentation of benzophenone
Authors: Srzić Dunja , Martinović Suzana , Vujanić Predrag , Meić Zlatko
Published: May 2005

The hydrogen and carbon randomization in the mass spectrometric behaviour of benzophenone has been studied by deuterium and 13C‐labelling. Hydrogen scrambling is involved only in the reactions of primary loss of hydrogen from molecular ions, as well as in secondary elimination of two hydrogen atoms from [MCO]+· ions. The carbon randomization does not feature in benzophenone upon electron impact.
Antisense DNA oligonucleotides I: The use of ionspray tandem mass spectrometry for the sequence verification of methylphosphonate oligodeoxyribonucleotides
Authors: Baker Timothy R. , Keough Thomas , Dobson Roy L. M. , Riley Timothy A. , Hasselfield Jody A. , Hesselberth P. Eric
Published: May 2005

The sequences of synthetically prepared methylphosphonate oligodeoxyribonucleotides have been verified using ionspray tandem mass spectrometry with sample introduction via flow injection. The technique involves the use of product‐ion scans from multiply protonated (4+ and 5+) precursors. Among the ions detected are several series of fragments of different charge states that indicate the base sequence of the intact molecule. Oligomers as large as 18 bases have been successfully characterized.
Antisense DNA oligonucleotides II: The use of matrix‐assisted laser desorption/ionization mass spectrometry for the sequence verification of methylphosphonate oligodeoxyribonucleotides
Authors: Keough Thomas , Baker Timothy R. , Dobson Roy L. M. , Llacey Martin P. , Riley Timothy A. , Hasselfield Jody A. , Hesselberth P. Eric
Published: May 2005

Matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry has been used to measure accurately the molecular masses of synthetic methylphosphonate oligodeoxyribonucleotides, up to 18 nucleotides in length. A simple method has been developed for the complete sequence verification of these compounds, which are intractable by classical means. Sequencing from the 5′ end of the molecule is possible because of inefficiencies in the synthetic procedure. Complementary information from the 3′ end can be obtained by partial hydrolysis of the methylphosphonate backbone.
Determination of sulfated peptides via prompt fragmentation by UV matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Talbo Gert , Roepstorff Peter
Published: May 2005

Determination of sulfation on peptides is difficult by biochemical methods if only a few picomoles of sample are available. By varying the laser irradiance, matrix‐assisted laser desorpiion/ionization mass spectra were obtained containing fragment ions diagnostic of sulfation.
A novel differentially pumped design for atmospheric pressure ionization‐ion trap mass spectrometry
Authors: Mordehai Alex V. , Henion Jack D.
Published: May 2005

A novel differentially pumped design for atmospheric pressure ionization (API)‐ion trap mass spectrometry is described. The vacuum system consists of three stages of pumping: API interface stage (1060 L/min), ion trap vacuum region (520 L/s) and electron multiplier region (60 L/s). The ion trap vacuum chamber has been specially designed to implement differential pumping of the ion trap and electron multiplier regions thus allowing ion trap operation with unit mass resolution at pressures up to 6 × 10−3 Torr of helium while maintaining high vacuum in the electron‐multiplier detector region. Trapping efficiency for accumulating externally produced ions was studied at unusually high pressures of the damping gas (helium) up to a pressure of 7 × 10−3 Torr (medium vacuum region). The trapping efficiency for externally produced ions and hence the overall mass spectrometric sensitivity is significantly improved by the introduction of helium damping gas into the ion trap region up to 6 × 10−3 Torr.
Quantitative trace analysis by combined chromatography and mass spectrometry using external and internal standards
Authors: Boyd R. K.
Published: May 2005

This review covers established methods for trace organic analysis by quantitative Chromatography. Although these methods are of more general applicability, they are widely used in practice with mass spectrometric detection. In the important class of methods employing surrogate internal standards (usually isotopically labelled versions of the target analytes), mass spectrometry is almost always obligatory in view of the inability to chromatographically resolve such a standard from the analyte in all but a few exceptional cases. The relative strengths and weaknesses of the methods are compared, and distinctions are drawn between ‘best’ methods for different circumstances, e.g., quality control of pharmaceutical preparations compared with analyses of environmental samples.
The 1,2‐phehyl migration of deprotonated benzyldiphenylamine in the gas phase
Authors: Reeks Lachlan B. , Dua Suresh K. , Bowie John H.
Published: May 2005

Deprotonated benzyldiphenylamine and its ring‐substituted benzyl derivatives undergo the nitrogen analogue of the Wittig rearrangement in the gas phase to form deprotonated benzhydrylanilines as product anions. The analogous process occurs under base‐catalysed conditions in the condensed phase. The collision‐induced loss of benzene from the rearrangement ion is used as a probe for the rearrangement. It is proposed that this is a stepwise reaction in which the second step (the deprotonation of the CH position by the incipient phenyl anion) is rate‐determining.
Formation of giant fullerene gas‐phase ions (C, 60 ⩽ 2n ⩽ 500): Laser desorption/electron ionization Fourier‐transform Ion cyclotron resonance mass spectrometric evidence
Authors: Wood Troy D. , Van Cleef Garrettt W. , Mearini Michael A. , Coe James V. , Marshall Alan G.
Published: May 2005

Laser desorption (followed by electron ionization) Fourier‐transform ion cyclotron resonance (LD/EI‐FTICR) mass spectra have been obtained for thin and thick deposits of purified C60 as well as benzene extracts of fullerene‐laden arc‐welded graphite soot under identical mass spectral conditions. Thick (but not thin) deposits exhibit ‘giant fullerene’‐like carbon cluster‐ion distributions, in either positive‐ or negative‐ion mode; giant fullerene ions observed by mass spectrometry therefore do not necessarily prove that neutral giant fullerenes were present in the original sample, which is consistent with recent laser vaporization and plasma desorption mass spectrometry results. FTICR‐MS of the residual soot remaining after benzene extraction yielded much more abundant ‘giant fullerene’ ions extending above C, which are probably derived both directly from the corresponding giant neutral carbon clusters in the sample and by the nucleation process seen for thick deposits of the extracts. The results shown here firmly establish the importance of sample thickness in the mass spectrometric examination of fullerene soot.
Development of a laser microprobe fourier transform mass spectrometer with external ion source
Authors: Van Vaeck L. , Van Roy W. , Struyf H. , Adams F. , Caravatti P.
Published: May 2005

Laser microprobe mass spectrometry (LMMS) employs focused laser‐beam irradiation of solids and subsequent mass analysis of the ions produced. The technique is suitable for the local analysis of inorganic and organic constituents with a spatial resolution in the micrometer range. The Fourier transform mass spectrometer (FTMS) is an analyser of choice for LMMS because high mass resolution and accurate mass determination can be routinely achieved at adequate sensitivity. This paper describes the first LMMS instrument using FTMS with an external ion source. The design considerations and the experimental performance are described with respect to such analytical parameters as spatial resolution and sensitivity. A comparison between time‐of‐flight mass spectrometry and IT‐LMMS for diagnostic analysis of organic molecules is interpreted in terms of the ion formation processes. Finally, the analysis of a selected integrated circuit evidences the feasibility of local analysis with a spatial resolution of 5 μm.
Electron‐impact induced fragmentations of some quinazolinediones and benzoxazinones
Authors: Himottu Marja , Pihlaja Kalevi , Stájer Géza , Vainiotalo Pirjo
Published: May 2005

Mass spectral fragmentations of 3‐substituted 2,4(1H,3H)‐quinazolinediones, 2‐phenylimino‐4H‐3,l‐benzoxazin‐4‐ones and 2‐thioxo‐2,3‐dihydroquinazolidin‐4(1H)‐one were examined using metastable‐ion analy sis and exact mass measurements. The isomeric compounds were easy to distinguish from their mass spectra. For quinazolinediones, the most surprising feature was the loss of CO2 showing that a rearrangement due to anilino migration must occur in these compounds. In comparison, the benzoxazinones showed no elimination of carbon dioxide.
Reduction of space‐charging in the quadrupole ion trap by sequential injection and simultaneous storage of positively and negatively charged ions
Authors: Williams Jon D. , Cooks R. Graham
Published: May 2005

Experiments were performed to establish the effects produced by the sequential introduction and simultaneous trapping of large quantities of positive and negative ions in the quadrupole ion trap. Injection conditions were controlled so that the trap stored only positively charged ions, only negatively charged ions, or both positively and negatively charged ions. Improved peak shapes and mass resolution were observed in positive‐ and negative‐ion mass spectra without loss of ion signal when ions of opposite charge were present in the trap. These results indicate that space‐charging of the trap can be relieved by the addition of ions of opposite charge.
Kinetics of isobaric ion/molecule reactions determined by the flowing afterglow‐triple quadrupole technique
Authors: Brickhouse Mark D. , Chyall Leonard J. , Sunderlin Lee S. , Squires Robert R.
Published: May 2005

An experimental method is described for determining the kinetics of gas‐phase ion/molecule reactions involving reactant and product ions with the same nominal or exact masses (i.e., isobaric ion/molecule reactions) using a flowing afterglow‐triple qvadrupole instrument. The method involves formation of specific monitor ions in the triple quadrupole analyzer by collision‐induced dissociation, exothermic ion/molecule reactions or energy‐resolved ion/molecule reactions for use in determining the kinetics of reaction of one component of an isobaric ion mixture in the flow tube. The measured depletion of these types of monitor ions is shown to provide a reliable means of determining the rate coefficient for the overall reaction taking place when a neutral reagent is added to the flow reactor.