bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrospray ionization mass spectrometry coupled with size‐exclusion chromatography
Authors: Prokai Laszlo , Simonsick William J.
Published: May 2005

The coupling of electrospray ionization mass spectrometry with gel permeation chromatography (GPC) has been used for the separation of a commercial polydisperse mixture of octylphenoxypoly(ethoxy)ethanol. Stable electrospray conditions are obtained upon using, as GPC solvent, tetrahydrofuran containing 10−5−10−4M sodium salt which also provides for the formation of intact molecular ions through cationization. Selected‐ion chromatograms of sodiated species allow for the monitoring of the elution profiles of individual oligomers, and can be used for the calibration of the GPC.
Multiply pulsed collision gas for ion axialization in fourier‐transform ion cyclotron resonance mass spectrometry
Authors: Guan Shengheng , Marshall Alan G.
Published: May 2005

We present a new multiply pulsed collision‐gas technique forion axialization for Fourier‐transform ion cyclotron resonace (FTICR) high‐resolution mass analysis. Ions are axialized in the source trap of a dural‐trap FTICR spectrometer y aimuthal quadrupolar irradiation for several tens of seconds at a steady‐state pressure maintained y repeated pulses of coolision gas (argon), folowed by removal of the collision gas and detection at a much lower pressure after transfer to the analyzer trap. Magnitufe‐mode FTICR mass resolving power, m/Δm≈︁1770000, for [M + K]+ ions from laser‐desorbed/ionized leucne enkephalin at m/z 594 is demonstrated. This resolving power is the highest yet reported for a peptide with any type of laser desorption/ionization mass analyzer.
Characterization of melanins by pyrolysis/gas chromatography/mass spectrometry
Authors: Vas György , Vékey Károly , Czira Gábor , Tamás József , Favretto Donata , Traldi Piero , Bertazzo Antonella , Costa Carlo , Allegri Graziella
Published: May 2005

Various natural and synthetic melanins were studied by the pyrolysis/gas chromatography/mass spectrometry technique, using both resistive and Curie‐point heating. The results obtained by the two pyrolysis procedures are different and complementary. By means of Curie‐point pyrolysis, at long times and high temperatures low molecular weight gases are produced from various melanins; the yields of the common pyrolysis products are also dependent on the melanin under study. By resistive heating, higher molecular weight compounds are produced, mainly nitrogen and oxygen heterocyclic systems, and differences are still evident among the products from the different melanins.
Suppression effects on a reduction process in fast‐atom bombardment mass spectrometry
Authors: Murthy Vemisetty S. , Miller Jack M.
Published: May 2005

Various methods of suppression of the reduction process occurring in fast‐atom bombardment (FAB) mass spectrometry have been studied, using the organic dyes rhodamine B and methylene blue as reference compounds. Our results indicate that transition metal chlorides have a strong influence on the suppression of the reduction process, while stannous chloride exhibits a remarkable suppression effect despite being a strong reducing agent. We suggest that the metal radicals generated in glycerol solution are responsible for these suppression effects. This phenomenou strongly supports the mechanism of hydrogen radical addition to the substrate molecules, postulated earlier as the cause of the reduction process. Co‐solvents in the matrix have also been found to suppress the reduction ions along with other matrix‐interfering ions. These studies help shed some light on the FAB ionization mechanism.
Non‐linear resonance conditions and their relationships to higher multipole fields in ion traps and quadrupole mass filters
Authors: Wang Yang
Published: May 2005

Deviations of electrode shapes from pure quadrupole systems result in the superposition of higher multipole fields onto the quadrupole field. Non‐linear resonances are generated due to these higher multipole fields. These non‐linear resonances can be thought of as internal resonances, which must fulfil appropriate conditions. In this paper, general non‐linear resonance conditions for a time‐variable, three‐dimensional, non‐linear quadrupole system are derived, using previously described methods. The occurrence of resonances depends on the electrode shapes of the non‐linear quadrupole systems which control the weight factors of the higher multipole fields. With special electrode shapes, for example shapes with symmetry, the resonance effects are reduced. Different higher multipoles (for example, octopoles and dodecapoles) generate non‐linear resonances which fulfil different and/or the same resonance conditions. Each resonance condition can be described by resonance lines within the stable regions of the stability diagram. Resonant ion motion possesses the characteristic that groups of ion frequencies are simultaneously resonant. These properties are analyzed and corresponding results are given.
Analysing the complexation of amino acids and peptides with β‐cyciodextrin using electrospray ionization mass spectrometry
Authors: Camilleri Patrick , Haskins Neville J. , New Anthony P. , Saunders Martin R.
Published: May 2005

The formation of non‐covalently bound inclusion complexes between ß‐cyclodextrin and peptides containing aromatic acid residues has been confirmed by elcctrospray ionization mass spectrometry. This preliminary study has indicated that phenylalanine and tryptophan residues can form 1:1 complexes with ß‐cyclodextrin whereas no evidence for such a complex could be found for tyrosine residues. Bradykinin, which contains two phenylalanine residues, formed both 1:1 and 1:2 complexes.
Multiresidue pesticide analysis by ion‐trap mass spectrometry
Authors: Cairns Thomas , Chiu Kin S. , Navarro David , Siegmund Emil
Published: May 2005

The ion trap has been demonstrated to be able to detect and quantify 245 target pesticides extracted via the Luke method while providing concurrent confirmation of presence via full scan data at the sub‐ppm level. The precision and accuracy of the analytical approach was determined to be no greater than 15% relative standard deviation. A comparision study of over 100 incurred residues analyzed by the ion trap and gas chromatography with an array of element‐selective detectors has indicated that sample clean‐up will probably be necessary before quantification is acceptable for all target compounds. The data obtained using a combination of gas chromatography and mass spectrometry and presented for 250 target pesticides constitutes the basic information required to duplicate and extend the methodology.
High temperature mass spectrometric study of oxide systems and materials
Authors: Stolyarova V. L.
Published: May 2005

High temperature mass spectrometry is a powerful tool for studying the vaporization processes and thermodyna‐mic properties of different types of materials such as glasses, ceramics and coatings. This paper illustrates the main advantages of this method for investigations of oxide systems and the approaches available to predict the relative volatilities as well as the thermodynamic properties of materials based on these systems.
Reactions in the mass spectrometry of 2,4,6‐N‐tetranitro‐N‐methylaniline (tetryl)
Authors: Yinon Jehuda , Zitrin Shmuel , Tamiri Tsippy
Published: May 2005

Despite the presence of the ions at m/z 242 and m/z 243 in the electron ionization (EI) and chemical ionization (CI) mass spectra of tetryl, respectively, no such daughter ions were observed in the collision‐induced dissociation spectra of the M+· ion in EI and of the [M+H]+ ion in CI. This supports the thesis that these ions are formed through hydrolysis of tetryl to N‐methylpicramide in the ion source before ionization. It was found that the hydrolysis is considerably stronger under CI consitions, but can be minirnized in EI. The structure of the molecular ion at m/z 242 in the EI mass spectrum of N‐methylpicramide was found to be similar to that of the [MH‐NO2]+ ion in the CI mass spectrum of tetryl.
Quantification of abscisic acid using liquid chromatography/thermospray ionization tandem mass spectrometry for selected reaction monitoring
Authors: Okamoto Masahiko , Takahashi Ken‐ichi , Doi Tadashi
Published: May 2005

A liquid chromatography/thermospray ionization tandem mass spectrometry (LC/TSP‐MS/MS) method was developed for the quantification of abscisic acid (ABA) in crude plant extracts without derivatization. By this technique interfering chemical background ions are eliminated and a detection limit for ABA olf 0.2 ng is achieved. Reproducibility for quantification is attained by parallel reaction monitoring of ABA and added ABA‐d6 used as an internal standard. The standard curve is linear over the range 200 pg to 10 ng of injected ABA. As examples of the application of the methodology, the quantification of ABA in some plant tissues is given.
Multiresidue pesticide analysis by ion‐trap technology: A clean‐up approach for mass spectral analysis
Authors: Cairns Thomas , Luke Milton A. , Chiu Kin S. , Navarro David , Siegmund Emil G.
Published: May 2005

Previous studies using the ion trap as a potential replacement for an array of element‐sensitive detectors indicated that only semi‐quantitative results at the 50–100 ppb range could be obtained for 245 pesticides because of interfering endogenous sample matrix compounds. The development of a new clean‐up procedure for a wide range of fruits and vegetables, specifically for use in an ion trap, has been undertaken to improve recoveries at the low ppm level to within analytically acceptable ranges (80–120%). This clean‐up involved the use of three solid‐phase extractions. The use of a C‐18 SepPak column removed the majority of hydrocarbon‐like molecules while the anion‐exchange column (QMA) removed all colored compounds and flavors, and finally the use of an aminopropyl column removed all sugars. Preliminary results from this study using 24 selected pesticides in four different sample matrices have indicated an acceptable improvement over previous results.
Simultaneous isolation of two different m/z ions in an ion‐trap mass spectrometer and their tandem mass spectra using filtered‐noise fields
Authors: Kenny Donald V. , Callahan Patrick J. , Gordon Sydney M. , Stiller Steven W.
Published: May 2005

For the first time, molecular ions from two different compounds have been simultaneously isolated in an ion‐trap mass spectrometer and their subsequent tandem mass spectra (MS/MS) obtained. Isolation was achieved by applying a filtered‐noise field (FNF) to the end‐caps of a FinniganMAT ion‐trap mass spectrometer (ITMS) using the Teledyne MEC/Hitachi HST‐1000 Enhancement Kit. The HST‐1000 generates a broadband waveform that would normally eject all ions from the trap. However, by setting notches in the waveform that correspond to certain resonant frequencies, individual masses can be isolated and stored in the trap without the need for the conventional DC voltage on the ring electrode. Using this FNF technique, the molecular ions of p‐dichlorobenzene (m/z 146) and 1,3,5‐trimethylbcnzene (m/z 120) were simultaneously isolated from a 42‐component mixture of volatile organic compounds. Each molecular ion was collisionally dissociated by applying a resonance excitation (‘tickle’) voltage from the HST‐1000, and the spectrum for each molecular ion was obtained by scanning the RF voltage to the ring electrode.
Quantitative analysis of low molecular weight compounds of biological interest by matrix‐assisted laser desorption ionization
Authors: Duncan Mark W. , Matanovic Gabrijela , Cerpa‐Poljak Anne
Published: May 2005

Internal standards were used to demonstrate that matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry can be applied to the quantitative analysis of low molecular weight polar compounds. Three examples were tested: a standard curve for 3,4‐dihydroxyphenylalanine (DOPA) was prepared using a stable isotope analogue (i.e., [13C6]DOPA) as an internal standard; [2H16]‐acetylcholine was employed as an internal standard for the quantification of acetylcholine; and in the final example, the peptide Ac‐Ser‐Ile‐Arg‐His‐Tyr‐NH2 was used as an internal standard for the quantification of the peptide H‐Ser‐Ala‐Leu‐Arg‐His‐Tyr‐NH2. In each instance, straight line fits (r2>0.95) demonstrate that MALDI is a viable approach for the quantitative analysis of low molecular weight analytes.
Multiresidue analysis of sulfonamides using liquid chromatography with atmospheric pressure chemical ionization mass spectrometry
Authors: Doerge Daniel R. , Bajic Steve , Lowes Steve
Published: May 2005

Sulfonamide antibiotics are widely used to prevent bacterial infections in livestock, and residues are commonly found in milk and meat. This is of toxicological and regulatory concern because sulfamethazine produces thyroid tumors in rodents. Unadulterated milk was purified using solid‐phase extraction and six sulfonamides were added prior to analysis by liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry. The mass spectra of all sulfonamides consisted exclusively of protonated molecules at low sampling cone voltage and, under these conditions, estimated detection limits were 0.05–0.5 ng, corresponding to 0.25–2.5 ppb in milk. The response curve for sulfamethazine was linear over a concentration range (1.25–20 ppb) that encompasses the regulatory level of interest in milk (10 ppb). Increasing the sampling cone voltage caused collision‐induced dissociation of sulfonamides that resulted in formation of ions that are diagnostic for the variable heterocyclic base and constant sulfanilyl portions of the molecule. At intermediate sampling cone voltages, multiple fragment ions were formed with reproducible intensity ratios. This process can be used to provide additional confirmation of target sulfonamides. Monitoring a common fragment ion formed at high sampling cone voltage permitted class‐specific multiresidue detection of the six sulfonamides with minimal losses in sensitivity. An analytical method is proposed for the detection, confirmation and quantification of sulfonamides and metabolites in milk with sensitivity equal to or greater than those obtained with less specific methods involving liquid chromatography with a UV detector. The relative simplicity of this technique and the availability of benchtop instrumentation suggests that routine screening and confirmation analyses of sulfonamide contaminants in milk is practicable.
Laser‐desorption Fourier‐transform mass spectrometry of triazines adsorbed on solid‐phase extraction membranes
Authors: Krier G. , Masselon C. , Muller J. F. , Nélieu S. , Einhorn J.
Published: May 2005

Until the present, analysis of aqueous solutions of atrazine has been conducted using a combination of liquid chromatography or gas chromatography with mass spectrometry, after a preconcentration step. We explore herein a new approach for studying support‐phase‐extracted atrazine and hydroxyatrazine samples. Solid‐phase extraction membranes are inserted directly into the cell of a Fourier‐transform mass spectrometer for analysis after laser ionization. It appears that atrazine and its metabolite have very different ionization processes. In the case of hydroxyatrazine, the [M + H]+ ion signal can be correlated to the concentration of the extracted solution. These encouraging results might open the route to a quantification method.
The Fourier‐transform laser microprobe mass spectrometer with external ion source as a tool for inorganic micro‐analysis
Authors: Struyf Herbert , Van Roy Wim , Van Vaeck Luc , Van Grieken René , Caravatti Pablo
Published: May 2005

Focused‐laser ionization of solids and subsequent analysis of the generated ions by Fourier‐transform mass spectrometry is suitable for the characterization of inorganic and organic constituents. This paper describes selected examples to illustrate the capability of structural characterization of inorganic substances and the problems associated with the critical nature of the energy deposition phenomena which can complicate the use of the method. Selected examples from practical problem solving in material applications are presented to evidence the feasibility of local analysis by Fourier‐transform laser microprobe mass spectrometry.
Desorption—ionization of organic compounds studied by Fourier‐transform laser microprobe mass spectometry
Authors: Van Roy Wim , Struyf Herbert , Van Vaeck Luc , Gijbels Renaat , Caravatti Pablo
Published: May 2005

The recently developed FT LMMS with an external ion source has been applied to selected organic molecules. Some aspects of the ion formation processes from solids under focused laser irradiation at 266 nm were investigated. Specifically, the effect of laser energy and the time profile of ion production were studied. First, the generation of intact cations, fragments and thermal decomposition products from a quaternary ammonium salt were evaluated at distinct times after the laser pulse. The mass spectra of phenol red in its neutral and salt form were recorded under different conditions with respect to laser irradiation power density conditions and ion formation after the laser pulse. The results allow the refinement of previous concepts about ionization in LMMS.
A regiospecific cycloaddition: Successive reactions of ·CH2CH2OH with CH2O
Authors: Mourgues Philippe , Audier Henri Edouard , Hammerum Steen
Published: May 2005

Four dominant reactions can be observed when the β‐distonic ion ·CH2CH2OH reacts in the cell of a Fourier‐transform ion cyclotron resonance spectrometer with a number of neutral molecules: protonation of the neutral molecule, ethylene radical‐cation transfer, hydride abstraction from the neutral molecule, and charge exchange. Among the ethylene transfer reactions, which can lead to a variety of other distonic ions, we have throroughly studied the reaction with formaldehyde. The reaction of a first molecule of CH2O yields ·CH2CH2OCH. The addition of a second one leads to 1,3‐dioxane which stabilizes by H· loss. This latter reaction is regiospecific.
Laser‐desorption Fourier‐transform mass spectrometry of [Ta6X12]X2·8H2O, X=C1, Br
Authors: Srzić Dunja , Tolić Ljiljana Paša , Martinović Suzana , Plavšic Dejan , Klasinc Leo
Published: May 2005

The gas phase of hexanuclear Ta clusters of type [Ta6X12]X2·8H2O, X=Cl, Br was investigated using laser‐desorption Fourier‐transform mass spectrometry. The [Ta6X12]Xions (m/z=1581 for X=Cl,m/z=2205 for X=Br) are the most characteristic peaks in their negative‐ion laser‐desorption mass spectra. Additional fragmentations observed are the result of loss of halogen and metal from [Ta6X12]X. Positive ions are observed only in the laser‐desorption mass spectra of [Ta6Br12]Br·8H2O.
Fast‐atom bombardment mass spectrometry of new polydentate schiff bases. 1. The case of variously substituted mono‐and bis‐salicylaldimine derivatives
Authors: Catinella S. , Traldi P. , Guerriero P. , Tamburini S. , Vigato P. A.
Published: May 2005

The mass spectrometric behaviour of ten variously substituted mono‐ and bis‐salicylaldimine derivatives has been studied by fast‐atom bombardment and metastable‐ion studies. In general, well detectable protonated molecules are present and fragmentation processes mainly related to aldimine chain cleavages are evidenced. Interesting cyclization reactions leading to particularly stable product ions are discussed.
Investigation of a series of neuroactive glycine dipeptide derivatives by fast‐atom bombardment and mass‐selected collision‐induced dissociation mass spectrometry
Authors: Henczi Maria , Weaver Donald F. , Borossay József
Published: May 2005

Glycylglycine (glygly) and 40 related acetamide derivatives were synthesized and investigated by fast‐atom bombardment mass spectrometry. The protonated molecules were mass selected and their collision‐induced dissociations were analyzed by tandem mass spectrometry. The data obtained allow a fragmentation pattern to be established for these glygly analogues and permit detailed structural information on the main fragment ions to be ascertained.
Multinuclear ions of ferrocene [Fen(C5H5)n+1]+ (n = 2, 3 and 4) in the gas phase identified by mass spectrometry
Authors: Tu Ya‐Ping , Wu La‐Duo
Published: May 2005

Under methane chemical ionization conditions, multinuclear ions of ferrocene [Fen(C5H5)n+1]+ (n = 2, 3 and 4), resulting from the ion/molecule reactions in the gas phase, were detected by mass spectrometry. Structures for these ions are elucidated, according to their mass‐analyzed ion kinetic energy spectra, to be triple‐, quadrupole‐, and quintuple‐decker sandwiches, respectively, and the formation pathways for them are also discussed.
Collision‐induced dissociations of three C3H3O− isomers. An interesting hydride‐transfer reaction
Authors: Dua Suresh , Bowie John H.
Published: May 2005

The major collision‐induced fragmentation of CH2CC(H)(O−) occurs following hydride transfer to form CH2CH−CO which then loses carbon monoxide to form deprotonated ethene (C2H).
Matrix‐assisted laser desorption/ionization of restriction enzyme‐digested DNA
Authors: Tang K. , Allman S. L. , Chen C. H. , Cháng L. Y. , Schell M.
Published: May 2005

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

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

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

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

High‐resolution translational energy spectra have been obtained for Ar2+ ions resulting from single‐electron capture by 9 keV Ar3+ ions in argon and xenon gas targets. Our result for Ar3+ in argon is broadly in agreement with previous high‐resolution studies, but we have further successfully assigned reaction channels to three peaks which were previously observed but not definitively identified. These channels appear to involve capture of a 3s‐electron from the target argon atom to form Ar+ ions in the first excited state Ar+[3s3p6 2S]. The capture spectrum for Ar3+ in xenon displays eleven relatively well defined peaks with exothermic energy changes in the range of 4–12 eV. However, these capture channels are difficult to identify with certainty because they involve capture into closely spaced high excited states of Ar2+, and are further complicated by the splitting (1.31 eV) of the ground‐state doublet 2P target Xe+ product ion. There are over one hundred competing channels, comprising three entrance and over forty exit channels, within this range of energy change. Tentative assignments of capture channels have been made, guided by electron‐core configuration and spin‐conservation requirements.
Gas‐phase rearrangements involving homoenolate anions. The isocamphanone/camphor rearrangement
Authors: Eichinger Peter C. H. , Bowie John H.
Published: May 2005

Deprotonated isocamphanones rearrange to deprotonated camphor in the gas phase, presumably via the intermediacy of a homoenolate anion.
Gas chromatography/combustion/isotope‐ratio mass spectrometry analysis of urinary steroids to detect misuse of testosterone in sport
Authors: Becchi Michel , Aguilera Rodrigue , Farizon Yves , Flament Marie‐Magdeleine , Casabianca Hervé , James Patrick
Published: May 2005

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Mixed‐oxide coatings are extensively used in the electrochemical industry. Secondary‐ion mass spectrometric data confirm that technological research can indeed find a new way of controlling precursors, synthesis conditions, purity of coatings and electrodic activity. Results obtained by argon and oxygen primary‐ion bombardment of RuO2/TiO2, IrO2/TiO2, RuO2/IrO2/TiO2 films are reported. The presence of metal, metal oxide and cluster ions suggests a more systematic use of secondary‐ion mass spectrometry in the elucidation of catalytic aspects. In‐depth profiles of some ionic species and their correlation with parameters that induce significant modifications can help in the understanding of the solid state physics and inorganic chemistry involved.
Structure‐dependent mass displacements in ion‐trap experiments
Authors: Bortolini Olga , Traldi Pietro
Published: May 2005

An overview of the phenomenon of mass displacement, observed in ion‐trap experiments, is given. In particular, the dependence of mass shifts upon the structures of the ions under investigation is discussed in detail and rationalized in terms of polarizability.
Picolinic acid as a matrix for laser mass spectrometry of nucleic acids and proteins
Authors: Tang K. , Taranenko N. I. , Allman S. L. , Chen C. H. , Chág L. Y. , Jacobson K. B.
Published: May 2005

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

Matrix‐assisted laser desorption/ionization using a 3‐hydroxpicollinic acid matrix from an active Nafion substrate has been used for detection of restriction enzyme‐degested double‐stranded plasmid DNA using time‐of‐ flight mass spectrometry. DNA strands of up to 267 base pairs were detected with minimal sample purification, although only as species corresponding to single‐stranded DNA.
Electrospray mass spectrometry on a magnetic sector instrument applied to heteropolyacids
Authors: Tuoi Jérémie Le Quan , Muller Etienne
Published: May 2005

Electrospray mass spectrometry has been applied to ionic inorganic systems such as heteropolyacids in methanol + water (1/1) or acetonitrile + water (1/1) solutions. Negative‐ion mass spectra were obtained on four different heteropolyacids. Heteropolymolybdates H3PMo12O40 and H4PMo11VO40 and heteropolytungstates H3PW12O40 and H4SiW12O40 gave ions with different charges. H3PMo12O40 gave ions of m/z 1822, 912 and 608 which correspond respectively to [PMo12O + 2H+], [PMo12O + H+]2− and [PMo12O40]3− ions. Resolution of 1:2200 has demonstrated the charge of each ion acquired. Furthermore, the isotope distribution of the observed ions was in good agreement with theory. Thus, electrospray mass spectrometry has become a powerful soft ionization technique for the analysis of such ionic compounds, provided they are soluble and stable in the solvent system used.
Ultramark 1621 as a calibration/reference compound for mass spectrometry. II. Positive‐ and negative‐ion electrospray ionization
Authors: Moini Mehdi
Published: May 2005

Electrospray ionization of solutions of Ultramark 1621, a commercially available mixture of fluorinated phosphazenes, in solution of 50:23:23:4 v/v of acetonitrile+water+methanol+acetic acid, produced a series of intense singly charged peaks in the m/z range of 900 to ca. 2200 in both positive‐ and negative‐ionization modes. The chemical compositions and accurate masses of ions in both positive‐ and negative‐ion spectra have been reported. An accuracy of approximately 2 ppm has been achieved for the average molecular weight of bovine insulin using Ultramark 1621 peaks as reference standards.