bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐Equilibration of the [MH]− ions of isomeric dimethylsulphone and methyl methylsulphinate
Authors: Dua Suresh , Bowie John H.
Published: May 2005

The collision‐induced dissociations of −CH2S(O)2CH3, −CD2S(O)2CH3 and −CH2S(O)OCH3 indicate that (i) a sulphone/sulphinate ester rearrangement does not occur for these systems, (ii) proton transfer accompanying or preceding the fragmentation of the [M  H]− ion of the sulphone is a minor process, and (iii) the characteristic fragmentations of −CH2S(O)2CH3 and −CH2S(O)OCH3 form [CH2S(O)2]−. and HCSO− respectively.
Studies on non‐covalent associations of immunosuppressive drugs with serum albumin using pneumatically assisted electrospray ionization mass spectrometry
Authors: Bakhtiar Ray , Stearns Ralph A.
Published: May 2005

Pneumatically assisted electrospray ionization (ion‐spray) mass spectrometry was employed in the detection of non‐covalent interactions of immunosuppressive drugs with proteins. Non‐covalent complexes of albumin (rat and bovine) with FK506, dihydro‐FK506, and FK520 were observed. No complexation was detected between albumin and cyclosporin A (CsA), even at a protein‐ligand molar ratio of 1:20. It is suggested that the lack of detection of an albumin–CsA non‐covalent complex may be attributed to dissociation of the weakly associated species during ion vaporization. Nonetheless, preliminary results indicate that ion‐spray mass spectrometry has potential in qualitative evaluation of drug–plasma protein interaction.
Electron impact, metastable ion and CID spectra of some thieno[2,3‐d]‐1,3‐dithioles and thieno[3,4‐d]‐1,3‐dithioles
Authors: Rovira Concepció , Tarrés Judit , Dias Marylène , Garín Javier , Orduna Jesús
Published: May 2005

The mass spectra of 1,3‐dithiole‐2‐thione‐ and tetrathiafulvalene‐fused thiophenes have been studied. Isomer differentiation was achieved by electron impact, metastable ion and collision‐induced dissociation spectra.
Liquid chromatography/mass spectrometry with collision‐induced dissociation of arachidonic acid metabolites derivatized with aminobenzenesulphonic acid
Authors: Yang Y. , Griffiths W. J. , Lindgren J. Å. , Sjövall J.
Published: May 2005

A fused‐silica capillary high‐performance liquid chromatography column (i.d. 0.25 mm) packed with octadecylsilane‐bonded silica has been used on‐line with continuous‐flow negative‐ion fast‐atom bombardment (FAB) mass spectrometry for the separation and structural analysis of series of fatty acids and arachidonic acid metabolites derivatized with 4‐aminobenzenesulphonic acid. Negative‐ion FAB spectra of the derivatized lipids showed strong [MH]− pseudomolecular ions. Collision‐induced dissociation of these anions produced structurally informative daughter ions, arising from charge‐remote fragmentations.
Detection of hydrogen‐bonded supramolecular complexes using electrospray ionization from chloroform
Authors: Cheng Xueheng , Gao Quanyin , Smith Richard D. , Simanek Eric E. , Mammen Mathai , Whitesides George M.
Published: May 2005

The stoichiometry of a noncovalent, hydrogen‐bonded supramolecular complex, hub(M)3·RCA3, was characterized using electrospray ionization from chloroform. The intact (1:3) complex was observed in the negative‐ion mode as a Cl−‐bound species using Ph4PCl as the source of the charge donor. Collisionally and thermally induced dissociation of the (1:3) complex resulted in the simultaneous loss of all the three RCA units, indicating a cooperative binding of RCA units in the (1:3) complex. These results suggest that the attachment of small, organic‐soluble ions may be a useful technique for mass spectrometric characterization of neutral supramolecular complexes that are stable or soluble only in non‐polar organic solvents.
Measurements of dication lifetimes by translational energy spectrometry
Authors: Safvan C. P. , Mathur D.
Published: May 2005

A new application of mass spectrometry to experimental studies of molecular dynamics has been developed and implemented in which ion translational energy spectrometry at very high angular resolutions is utilized to study the unimolecular dissociation of metastable dications. A brief overview is presented of the experimental technique, which utilizes a ‘home‐made’, three‐sector (equivalent to BEE geometry) instrument. The fragmention kinetic energy spectrum obtained using such apparatus is capable of yielding information on the lifetimes of specific quantal states of dications of a wide variety of stable and radical species; two illustrative examples (CO2+ and SH2+) are presented.
Dissociative attachment studies by negative‐ion time‐of‐flight mass spectrometry
Authors: Krishnakumar E. , Nagesha K.
Published: May 2005

Experiments using time‐of‐flight mass spectrometry for studying the formation of negative ions in dissociative attachment processes by electron impact are discussed. The problems of making accurate measurements of absolute partial cross‐sections have been solved using a combination of a new pulsed‐electron‐beam/pulsed‐ion‐extraction technique, the relative flow technique and a time‐of‐flight mass spectrometer. We also discuss some of the results obtained utilizing this method.
Dissociation dynamics of molecular ions in very high charge states
Authors: Mathur D. , Safvan C. P. , Krishnamurthy M.
Published: May 2005

An attempt is made to relate the dissociation dynamics of highly charged molecular ions (possessing charges in excess of 2+) to molecular structure. High‐level, ab initio configuration‐interaction calculations are carried out of the potential energy functions of N, for q = 2–12, and predictions are made of the values of the kinetic energies released upon unimolecular dissociation of such ions. The calculated values are found to be significantly lower than those expected from simple Coulombic considerations. Electron density distributions of highly charged molecules are calculated and, on the basis of these, a long‐lived state of a diatomic tri‐cation, CS3+, is predicted. Mass spectrometric evidence is produced which confirms these predictions.
Structural characterization of glutaminergic blocker spider toxins by high‐energy collision charge‐remote fragmentations
Authors: Fujita Tsuyoshi , Itagaki Yasuhiro , Naoki Hideo , Nakajima Terumi , Hagiwara Ken'ichi
Published: May 2005

Spider venom gland stores various glutaminergic blockers such as acylpolyamines, besides proteins and peptides. A method is described for structure determination of these acylpolyamines using fast‐atom bombardment and four‐sector tandem mass spectrometry. The collision‐induced dissociation (CID) spectra of protonated molecular ions of synthetic model compounds show only a small number of weak, sequence‐related product ions. But, unlike the CID spectra of [M + H]+ ions, dissociation of sodium‐attached molecular ions leads to charge‐remote fragmentations and provides intense sequence‐related product ions.
Structure of the diene originating from a retro‐Diels–Alder cleavage, of the natural product kuwanon g
Authors: Takayama Mitsuo , Nomura Taro , Nojima Kazutetsu
Published: May 2005

Fragmentation of a natural Diels–Alder adduct, kuwanon G, has been examined using fast‐atom bombardment and collision‐induced dissociation (CID) techniques. The CID spectrum of a diene ion originating from a retro‐Diels–Alder cleavage of the [M + H]+ ion gave an intense peak arising from the fragmentation of the diene moiety, as well as characteristic peaks arising from the fragmentation of a tautomeric 2,2‐dimethylpyran ring structure. The results obtained suggest that the diene can be irreversibly converted into the 2,2‐dimethylpyran ring structure under gas‐phase mass spectrometric conditions.
Graphical method for artefact peak interpretation, and methods for their rejection, using double and triple sector magnetic mass spectrometers
Authors: Mouget Yves , Bertrand Michel J.
Published: May 2005

The problem of artefact peaks, in spectra obtained from various tandem mass spectrometric scans on instruments of both forward and reverse geometry, is examined. The filtering conditions imposed by additional analyzers are investigated, in order to evaluate the potential of several different triple sector geometries to reduce specific interferences. No previous evaluation of the rejection ability for artefacts of different origins has been presented with respect to the various geometries. In order to gain a better insight into the origin of various artefacts, and to more easily explain their occurrence in certain geometries, a new graphical representation was developed in order to take into account the effects of three analyzer fields. This approach allows different linked scans to be projected within a cube, while also qualitatively proposing an explanation for the presence or absence of artefact peaks. New scans can also be conceived by means of this method, as is the case with a new selected mass ion kinetic energy (SMIKE) scan, which allows artefacts present in MIKE scans performed using reverse geometry instruments to be determined.
Desorption of ions from locust tissues. III. Study of a metabolite of A‐destruxin using fast‐atom bombardment linked‐scan mass spectrometry
Authors: Loutelier Corinne , Marcual Albert , Lange Catherine , Cherton Jean‐Claude , Cassier Pierre
Published: May 2005

The process of the detoxification of A‐destruxin into a polar linear peptide in vivo in Locusta migratoria has been demonstrated using both high performance liquid chromatography and negative‐ion fast‐atom bombardment mass spectrometry. The final structure of the metabolite, after synthesis and comparison of retention time with the component in the crude biological mixture, was elucidated by positive‐ion fast‐atom bombardment linked‐scan mass spectrometry. Diagnostic fragment ions produced by collision‐induced dissociation are discussed.
Paclitaxel metabolites in human plasma and urine: Identification of 6α‐hydroxytaxol, 7‐epitaxol and taxol hydrolysis products using liquid chromatography/atmospheric‐pressure chemical ionization mass spectrometry
Authors: Royer I. , Alvinerie P. , Wright M. , Monsarrat B. , Ho L. K. , Armand J. P.
Published: May 2005

Reversed‐phase high‐performance liquid chromatography/mass spectrometry (LC/MS), with an atmospheric‐pressure chemical ionization (APCI) interface, has been applied to the identification of metabolites and derivatives of paclitaxel (taxol) in plasma and urine of patients treated with this new anticancer drug. Protonated molecules with substantial fragmentation were obtained using this ionization technique. The three ion series observed are characteristic of the intact molecule, the taxane ring, and the side chain at C13. Their analysis gives information about chemical modifications of the taxane structure at different positions of the molecule. Urine and plasma extracts were evaluated using the capacity to perform MS analysis directly on the entire effluent from conventional LC columns. Excellent spectra were obtained with 50 pmol of separated compounds in full scan mode. This technique allowed highly sensitive identification of 6α‐hydroxytaxol, the major human biliary metabolite, and of 7‐epitaxol in extracts of plasma and urine from patients. Taxol hydrolysis derivatives were observed for the first time in urine 24 hours after the end of the infusion period. Sensitivity could be increased further using single ion monitoring (SIM) mode, once a target derivative was identified. These results demonstrate that LC/MS with an APCI interface is useful for the characterization and pharmacokinetic analysis of taxoids in biological matrices.
Determination of isoflavones using high‐performance liquid chromatography with atmospheric‐pressure chemical ionization mass spectrometry
Authors: Aramendía Maria Angeles , García Isabel , Lafont Fernando , Marinas Jose María
Published: May 2005

High‐performance liquid chromatography in combination with mass spectrometric detection (atmospheric‐pressure chemical ionization, APCI) was used to determine various isoflavones. Negative‐ion APCI ionization has proved to be a suitable technique for determining this class of natural compound, as it provides quality mass spectra which give not only the molecular weight of the isoflavones, but also their molecular structures; consistent collision‐induced dissociation pathways were elucidated and fragments are reported. Deuterium oxide was used to induce peak shifts in the mass spectra in order to determine the number of exchangeable hydrogen atoms in each molecule.
Collision‐induced fragmentation processes in some pesticides studied by tandem mass spectrometry
Authors: Yinon Jehuda
Published: May 2005

Tandem mass spectrometric (MS/MS) collision‐induced dissociation (CID) mass spectra of the molecular ion and main fragment ions in electron ionization of a series of pesticides were recorded using a triple quadrupole mass spectrometer. The fragmentation pathway map of simazine was deduced from the CID mass spectra. The utility of these CID fragmentation ions is demonstrated in the gas chromatography/MS/MS spectrum of carbofuran.
Fast‐atom bombardment mass spectra of the 132‐epimers of 132‐hydroxychlorophyll a
Authors: Kostiainen Risto , Hyvärinen Kristiina , Hynninen Paavo H.
Published: May 2005

Fast‐atom bombardment (FAB) mass spectra have been measured for resolved 132‐hydroxychlorophyll a epimers. The fragmentation of each epimer was studied by tandem mass spectrometry using linked scans at constant B/E. The FAB spectra showed a very intense radical cation (M+·) and EI‐type fragmentations. The most abundant fragment ions were formed by the losses of the phytyl, the 132‐hydroxy, and the 132‐methoxycarbonyl groups in various combinations. The fragment ions [M  OH]+, [M  phytadiene]+·, and [M  phytadiene  OH]+ were found to be characteristic of both 132‐hydroxychlorophyll a epimers. Nevertheless, it was shown that the loss of the 132‐hydroxy group occurs more easily from the 132(S)‐epimer than from the 132(R)‐epimer. This fragmentation difference offers a new possibility for the determination of the stereochemistry at the 132‐chiral centre of purified 132‐hydroxychlorophyll preparations.
Pyrolysis/gas chromatography/mass spectrometry of arsenic inorganic compounds
Authors: Chiavari Giuseppe , Fabbri Daniele , Galletti Guido C.
Published: May 2005

Pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS) of As4S6 (orpiment), As4S4 (realgar), As4O6 (arsenolite), NaH2AsO4 (sodium di‐H‐orthoarsenate) was performed using a platinum‐filament pyrolyzer heated at 700°C for 10 s and coupled to a capillary gas chromatograph/ion trap mass spectrometer. As4 was observed as a pyrolysis fragment in the pyrograms of all compounds. Pyrolysis of NaH2AsO4 equivalent to 100 ng of As, produced a strong As4 chromatographic peak. As4S3 and As4S4 were detected as pyrolysis products of As4S6 (orpiment). As4S4 (realgar) and As4O6 (arsenolite) were detected as intact molecules after pyrolysis. By contrast, intact As4S6 was not detected after pyrolyses in the range 400–700°C. As4 was detected as an impurity in the painting layer of an Egyptian mummy. The mass spectra of such arsenic compounds, none of which is included in the NIST library of spectra, are reported. Advantages and limitations of PY/GC/MS as a technique for the qualitative detection of arsenic inorganic compounds are discussed.
Mass spectrometry of lepidopterous insect sex pheromones containing a diene system
Authors: Yuan Gu , He Meiyu , He Xioran
Published: May 2005

The mass spectrometric behavior of some diene‐based sex pheromones of lepidopterous insects, under electron impact ionization conditions, was studied with the aid of mass‐analyzed ion kinetic energy spectroscopy and high‐resolution data. The similarity of the mass spectra of these dienes and their ability to distinguish double bond positional isomers and geometrical isomers was examined by a ‘minimum‐maximum’ similarity analysis.
Mass spectrometry of cyanocobalamine, glucose and raffinose in the solid state and on a disperse oxide surface
Authors: Pokrovskiy V. A. , Galagan N. P. , Dembnovetskaya L. I.
Published: May 2005

The biologically active systems were synthesized by adsorption of vitamin B12, glucose and raffinose on an ultrafine oxide surface and studied by means of thermal analysis and temperature‐programmed mass spectrometry. It is shown that adsorption of cyanocobalamine (B12) on the silica surface transformed the propionamide group to a weakly bound form. The role of the charged cobalt atom and of the propionamide and benzimide groups in the adsorption mechanism is discussed. Experimental data were obtained confirming the stable adsorption of glucose and raffinose on an ultrafine pyrogenic silica surface modified by amino groups.
Temperature‐programmed mass spectrometry of biomolecules in surface chemistry studies
Authors: Pokrovskiy V. A.
Published: May 2005

The peculiarities of the temperature‐programmed mass spectrometry (TPDMS) experimental technique are discussed with reference to studies of biologically active molecules absorbed on ultrafine oxide surfaces. Simple theoretical models are presented in order to allow an approximate analytical treatment of TPDMS data.
Analysis of C60 derivatives by fast‐atom bombardment mass spectrometry as γ‐cyclodextrin inclusion complexes
Authors: Juo Chiun‐Gung , Shiu Lung‐Lin , Shen Clifton Kwang‐Fu , Luh Tien‐Yau , Her Guor‐Rong
Published: May 2005

Many C60 derivatives form stable complexes with γ‐cyclodextrin in a ratio of 1:2. These complexes can be easily analyzed by fast‐atom bombardment mass spectrometry (FAB). Unlike the analysis of C60 derivatives directly by FAB, the spectra of these complexes were characterized by molecular ions with little or no fragmentation. The analysis of these complexes by FAB provides an easy and useful approach for the characterization of C60 derivatives. Most likely due to the size of the cavity, this approach is limited to C60 derivatives with molecular weights not significantly larger than that of C60 itself.
Experimental verification of an improved prefilter model
Authors: Simon M. , Bohátka S. , Futó I. , Trajber Cs.
Published: May 2005

The experimental verification of predictions of a new simulation model of quadrupole mass filters is presented. Computer calculations show that the transmission of the prefilter‐QMS system is periodical as a function of the prefilter length. The periodicity of the transmission is independent of the mass number of ions of equal velocity. Experimental proof of the simulation has been produced for low mass numbers and a more difficult procedure is required for higher masses (m/z > 100). This is realized with a closed ion source and tandem quadrupole mass spectrometer arrangement. Experimental results prove the mass‐independent behaviour predicted by the model.
Mass spectral study of diastereomers by electron impact
Authors: Vairamani M. , Prabhakar S. , Rama Devi A. , Madhusudanan K. P.
Published: May 2005

The electron impact mass spectra of some diastereomeric dialkyl tartrates and isopropylidine derivatives of dimethyl tartrate show diagnostic differences in the relative abundances of some ions. The differences have been explained based on preferred conformations of these isomers. The configuration of the carbomethoxy groups has been correlated with the configuration of carbomethoxy groups in dimethyl maleate and fumarate. The interaction between the two carbomethoxy groups is relatively larger in conformations where there is a gauche interaction between them. The results could also be correlated with the solution phase conformations of these compounds reported in the literature using nuclear magnetic resonance techniques. The difference, which is small in diastereomeric dimethyl tartrates, is very reproducible and has been confirmed using six different mass spectrometers.
Glycosyl compositions and structural characteristics of the potential immuno‐adjuvant active saponins in the Quillaja saponaria Molina extract Quil A
Authors: van Setten Dirk C. , van de Werken Gerrit , Zomer Gijsbert , Kersten Gideon F. A.
Published: May 2005

Fifty saponin components of Quil A, a commercially available extract from the bark of the South American tree Quillaja saponaria Molina, were partially structurally characterised. The molecular weights were determined by fast‐atom bombardment mass spectrometry. The glycosyl and elemental composition of all the saponins was determined by applying our recently developed method, monomer mapping, consisting of a computer program and accurate mass measurements. Support for the presumed identity of the aglycone, i.e. quillaic acid, was found in the accurate mass determination, 1H NMR measurement and chemical reactions. The saponin composition of Quil A was shown to consist of pairs. Within the 3‐O bound glycosyl moiety of a pair there was a structural difference: a pentose and rhamnose were interchanged. Structural differences between different pairs were located in the 28‐O bound glycosyl moiety. A structural element, unknown to date and of which the elemental composition was deduced to be C8H12O5, was found in the 28‐O bound glycosyl moiety of several saponins.
Negative‐ion electrospray mass spectra of peptides derivatized with 4‐aminonaphthalenesulphonic acid
Authors: Griffiths William J. , Lindh Ingemar , Bergman Tomas , Sjövall Jan
Published: May 2005

The detection limits of a series of small peptides derivatized with 4‐aminonaphthalenesulphonic acid have been determined using a magnetic sector mass spectrometer operated in the negative‐ion mode. The instrument (AutoSpec‐QFPD) is equipped with an electrospray ion source and both array and point detectors. Detection limits when using the array detector were on the sub‐femtomole level at a mass resolution of 2000 (full width half maximum height). Cone‐voltage and linked‐scan collision‐induced dissociation spectra were recorded using both the array and point detectors. When using the array detector, amino acid sequence information could be obtained from as little as 50 fmol of sample consumed.
High‐temperature mass spectrometric study of the thermodynamic properties of the CaOAl2o3 system
Authors: Stolyarova V. L. , Shornikov S. I. , Shultz M. M.
Published: May 2005

Using the Knudsen effusion mass spectrometric method, the composition of vapour and the partial pressures of vapour species over melts of the CaOAl2O3 system were studied for the temperature range 1833–2033 K. Thermodynamic functions of the CaOAl2O3 system were obtained, and the negative deviations from ideal behaviour were illustrated. The dependence of the Gibbs energies of formation of the CaOAl2O3 system on temperature and concentration of components was suggested.
The dependence of the resolving power and sensitivity of a discrete electrode detector array on the proximity of a microchannel‐plate electron multiplier
Authors: Langstaff David P. , Birkinshaw Keith
Published: May 2005

A detector array has been designed which integrates all pulse sensing, data logging, control and interface circuitry on a single silicon chip. In conjunction with a microchannel‐plate electron multiplier (MCP) the array can be used to measure dispersed spectra of ions, electrons and photons (UV and higher energies). In order to increase the sensitivity of the pulse sensing circuitry, non‐standard steps are introduced into the fabrication process which increase cost and prototype development time. In the present work it is shown that by reducing the separation between the MCP output and the array to about 4.5 microns an improvement in performance is achieved which should enable the production of high performance devices using a standard fabrication process.
Contribution of mass spectrometry to the structural confirmation of components of the antibiotic GE2270 complex
Authors: Colombo L. , Stella S. , Selva E.
Published: May 2005

The GE2270 complex consists mainly of GE2270 A (MW 1289), a thiazolyl peptide antibiotic whose structure originates from the modification of a chain of 14 amino acids in a process which creates six thiazole rings and one pyridine. Together with the main component, a number of structurally related molecules are co‐produced in small quantities by fermentation. A preparative high‐performance liquid chromatrography method was developed to isolate GE2270 factors B1, B2, C1, Ca, C2a, C2b, D1, D2, E and T. Their structures, preliminarily determined by 1H‐nuclear magnetic resonance spectroscopy in comparison with GE2270 A, were confirmed by low and high resolution fast‐atom bombardment mass spectrometry and studies on the intact molecules and on their main hydrolysis products. Their molecular weights range from 1246 to 1306 Da. The structural differences between the factors lie in the extent of methylation and/or oxidation of thiazole rings (D and E) and asparagine, and in the aromatization of the oxazoline ring.
Automation of data acquisition and processing involving dynamically programmed scanning for a quadrupole ion trap mass spectrometer
Authors: Clarke Nigel J. , Franklin Anthony M. , Langford Marian L. , Penman Andrew D. , Thorner David A. , Todd John F. J.
Published: May 2005

This paper describes the use of dynamically programmed scanning in the automation of the acquisition and processing of data using a quadrupole ion trap mass spectrometer. The programs written to carry out the fixedion tandem mass spectrometry experiments and to automate the production of the three‐dimensional graphs are described. The use of three‐dimensional graphs to display familial data is also discussed, with examples of spectra given.
Amino acid composition and wavelength effects in matrix‐assisted laser desorption/ionization
Authors: Olumee Zohra , Sadeghi Mehrnoosh , Tang Xiaodong , Vertes Akos
Published: May 2005

Ion yields were investigated in matrix‐assisted laser desorption/ionization (MALDI) as a function of amino acid composition using a variable wavelength ion source. In the case of nitrogen laser excitation (337 nm), [M+H]+ ions were abundant for short peptides containing basic or polar amino acid residues. The lack of basic residues led to diminishing ion formation at 337 nm. Increasing the chain length led to enhanced ionization even for peptides with non‐polar side chains. In contrast to the liquid phase basicities the basic residues showed Arg > His > Lys order in their affinity to protons. Variations in the average ion yield showed decreasing trend with increasing basicity of the residues pointing to potential differences in the matrix incorporation of different guest molecules. Dye laser excitation at 280 nm resulted in extensive fragmentation and enhanced ion formation from peptides containing aromatic side chains indicating the possible role of analyte excited states in ion formation. Semi‐empirical quantum chemical calculations were used to explore the sites of protonation. Heat of formation diagrams of the matrix‐analyte complexes were examined as a function of their configuration. Investigation of the optimized geometries allowed the location of bifurcated and linear hydrogen bonds between the non‐polar analyte (e.g., Gly‐Gly) and matrix molecules. In addition to these intermolecular bonds, in the case of His‐His an intramolecular hydrogen bond was also formed within the analyte molecule. Proton affinity values were calculated for every dipeptide while the site of protonation was varied. The results seemed to indicate that for every dipeptide the amino terminus was more susceptible to protonation than the peptide bond. Due to increased stabilization effects in homo‐oligomers (Glyn), increasing the number of residues led to an increase in proton affinity. For basic diopeptides (e.g., His‐His), the side chains had the highest proton affinity, underlining their role in MALDI of proteins.
Concentration dependence of nucleoside fast‐atom bombardment mass spectra
Authors: Aksyonov Sergey A. , Sukhodub Leonid F.
Published: May 2005

The quantitative investigation of the four RNA nucleosides (adenosine, guanosine, cytidine and uridine) using fast‐atom bombardment mass spectra is reported. Nucleoside concentrations are varied in the 0.8–4% range. The nucleoside hydrogen‐bonded complexes are shown to form primarily on the liquid matrix surface.
Mass spectral fragmentation patterns of some 2‐methyl‐3‐furancarboxanilides and 2‐methyl‐3‐furancarbothioanilides. II
Authors: Karminski‐Zamola Grace , Fis̆er‐Jakić Lelja , And Miroslav Bajić , Boykin David W.
Published: May 2005

The electron impact mass spectra of some 2‐methyl‐3‐furancarboxanilides and 2‐methyl‐3‐furancarbothioanilides are discussed. Dominant peaks are formed by simple cleavage of a CN bond in the anilides as well as in the thioanilides. Thioanilides show some additional fragmentation pathways recently reported which are not seen in the anilides. (T. Jagodzinski and M. Stobiecki, Org. Mass Spectrom., Vol. 25, p. 333 (1990)).
Fast‐atom bombardment mass spectrometry coupled with collision‐induced dissociation of a hydantoin series for fragmentation studies
Authors: Henczi Maria , Weaver Donald F.
Published: May 2005

Phenytoin is one of the most widely employed anticonvulsant drugs in the world. Because this drug has several side effects, an exhaustive structure‐toxicity study is needed. To find an easy and cost‐effective way to monitor phenytoin in metabolism and toxicity studies, 18 phenytoin derivatives were synthesized and analysed by fast‐atom bombardment tandem mass spectrometry.
Host–guest chemistry in the gas phase. Complexes of crown ethers with Fe(CO) ions
Authors: Gren' A. I. , Mazepa A. V. , Timofeev O. S.
Published: May 2005

The complexes formed between a series of 19 different crown ethers and Fe(CO) ions are described. It is found that the energy released in the reactions increases with the crown ether ring size. The bicyclic‐ring crown ethers can form sandwich type compounds with the reagent.
Fast‐atom bombardment mass spectrometry of 2,4‐diketonate complexes of transition metals [V(III), Cr(III), Mn(III), Fe(III), Co(III), Ru(III) and Os(III)]
Authors: Saraswathi Mandapati , Miller Jack M.
Published: May 2005

The tris(acetylacetonate) (L3) and tris(1,1,1‐trifluoromethyl‐2,4‐pentanedionate) (L′3) complexes of transition metals V, Cr, Mn, Fe, Co, Ru and Os in their +3 oxidation states were studied under fast‐atom bombardment (FAB) conditions using 3‐nitrobenzyl alcohol as a matrix. All complexes showed the formation of molecular ion and protonated molecules [ML2]+ and [ML′2]+ are the most abundant ions in the spectra of all the metal acetylacetonates (L) and trifluoroacetylacetonates (L′) studied. Interaction of matrix with metal complexes and polynuclear metal complexes led to the formation of polynuclear species with significant abundance especially for manganese and iron complexes. Formation of these metal ions was observed with relative intensities from 3–30%. Ions corresponding to ligand‐exchange reactions were observed with moderate to high abundance in all metal complexes studied except those of ruthenium and osmium. Experiments carried out with a split FAB probe tip suggested ligand–ligand exchange reactions were not due to gas‐phase reactions but only due to solution‐phase exchanges. Osmium and ruthenium complexes do not yield polynuclear species or ions due to matrix clustering. Instead they show neutral ligand losses and formation of acetyl ion.
Differentiation between natural and synthetic taurine using the 13C/12C isotope ratio
Authors: Gioacchini Anna Maria , Roda Aldo , Cipolla Antonio , Parenti Massimo , Baraldini Mario
Published: May 2005

Natural taurine is an essential constituent of formula milk for infants and, because of the inferior nutritional value (δ), of synthetic forms, it is important to discriminate between these and taurines derived from a natural source. In this study we evaluated the ability of a method to make this distinction; it consisted of determination of the taurine 13C/12C ratio by means of a precision automated continuous flow mass spectrometric apparatus. This method was found to provide a powerful analytical tool for this purpose.
Localized charge distributions in stable n‐hexane radical cations
Authors: de Koster Chris G. , Beijersbergen Jaap H. M.
Published: May 2005

The potential energy surface of n‐hexane radical cations is probed theoretically. The structures with low internal energies are characterized by extensive lengthening of one of the three innermost CC bonds. This CC bond stretch is induced by localization of the positive charge. For an elongated terminal CC bond we calculated an energy which is 0.4 eV higher than that for a stretched central CC bond. The n‐hexane geometries with several CC bonds stretched do not represent stationary points on the potential energy surface. Comparison with previous dissociative‐neutralization experiments of low‐internal‐energy n‐hexane ions shows that the fragmentation pathways reflect the two lowest energy structures.
New matrices and accelerating voltage effects in matrix‐assisted laser desorption/ionization of synthetic polymers
Authors: Tang Xiaodong , Vertes Akos , Dreifuss Peter A.
Published: May 2005

Most matrices used in matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) have been selected for their sound performance in the detection of proteins. We evaluated a series of new matrices for the analysis of synthetic polymers and compared their performance to that of conventional ones. Among substituted polycyclic aromatic hydrocarbons 1,4‐dihydroxy‐2‐naphthoic acid, 9‐anthracenecarboxylic acid (9‐ACA), and its mixtures with 5‐methoxysalicylic‐acid (‘super’ 9‐ACA) offered better signal quality for analysis of synthetic polymers. To test the performance of these new matrices, authentic standards of poly(ethylene glycol), poly(propylene glycol), Jeffamine, polybutadiene, poly(methyl methacrylate), poly(dimethyl siloxane), and some of their mixtures were analyzed. By generating mainly [M + Na]+ ions, 9‐ACA showed superior performance to most conventional matrices and provided higher effective mass resolution. The ‘super’ 9‐ACA composite matrix was found to be more suitable for larger polymer molecules (>8000 Da).

Broader acceptance of MALDI‐MS for synthetic polymer analysis has been delayed by systematic differences observed between MALDI‐MS and gel permeation chromatography (GPC) in terms of oligomer size distributions (R. S. Lehrle and D. S. Sarson, Rapid Commun. Mass Spectrom.), Vol. 9, p. 91 (1995). We found that part of the discrepancy can be explained by the profound dependence of mass distributions on the accelerating voltage of the time‐of‐flight mass spectrometer. With decreasing accelerating voltage both the ion intensity and the mass resolution decreased, and the high‐mass end of the mass spectrum became truncated. For example, when the accelerating voltage was changed from 30 kV to 18 kV the center of the peak area distribution for poly(methyl‐methacrylate) (PMMA) 6000 shifted to lower values by about 210 Da. At the same time, the skewness of the distribution increased tenfold indicating serious discrimination phenomena. These detrimental effects of lower accelerating voltage were particularly strong for relatively large synthetic polymer molecules.
Amino acid sequence determination of phosphoenkephalins using liquid secondary ionization mass spectrometry
Authors: Dass Chhabil , Mahalakshmi P.
Published: May 2005

Liquid secondary ionization mass spectrometry (LSIMS) operating in the positive‐ and negative‐ion modes was used to study fragmentation profiles and to obtain the amino acid sequences of a set of seven phosphoenkephalin peptides. The use of glycerol as the liquid matrix led to increase in fragmentation of phosphopeptides. The prominent amino acid sequence‐determining ions in the positive‐ion mode are y‐type C‐terminal ions; the N‐terminal sequence‐specific ions are observed sporadically. The most dominant ions in those mass spectra, however, are the immonium ions and a few low‐mass side‐chain cleavage products. The mass spectra in the negative‐ion mode are more information‐rich, and provide data complementary to that from the positive‐ion mode. The phosphate group marker ions, m/z 79 (PO) and 97 (H2PO), are prominent and both N‐ and C‐termini sequence ions are formed with equal facility in this mode of analysis. Both positive‐ and negative‐ion mass spectral data are useful in determining the amino acid sequence of all of the seven phosphoenkephalins. Thus, LSIMS alone can be a viable option to the tandem mass spectrometry approach when sufficient quantities (>50 nmol) of phosphopeptides are available.
Molecular weight distribution of poly(dimethylsiloxane) by combining matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with gel‐permeation chromatography fractionation
Authors: Montaudo Giorgio , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo
Published: May 2005

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) allows detection of large molecules such as those present in synthetic and natural macromolecules. Until recently, it was reported that MALDI‐TOF measurements can provide correct molecular weight (MW) estimates only for nearly monodisperse polymer samples. We have now developed a methodology for polydisperse samples. We recorded the gel‐permeation chromatography (GPC) trace of a polydisperse polymeric sample of poly(dimethylsiloxane) (PDMS), collecting 42 fractions. Selected fractions were analyzed by MALDI‐TOF and the average MW of each fraction was determined, allowing a calibration of GPC curves against absolute MW. The calibrated GPC trace was then used to compute average MW and molecular‐weight distribution (MWD) of the unfractionated poly(dimethylsiloxane) sample. In the spectra of low molecular‐weight fractions, the resolution is high enough to resolve the contributions of the various PDMS oligomers as separate signals.
Identification of chlorophyll transformation products in zooplankton faecal pellets and marine sediment extracts by liquid chromatography/mass spectrometry atmospheric pressure chemical ionization
Authors: Harris Philip G. , Eglinton Geoffrey , Carter James F. , Maxwell James R. , Head Robert N. , Harris Roger P.
Published: May 2005

Liquid chromatography/mass spectrometry with an atmospheric pressure chemical ionization interface permits the routine study of mixtures of algal‐derived, chlorophyll transformation products isolated from biological and environmental samples. Interpretation of the mass spectra of standards of chlorophyll a and three of its commonly occurring transformation products has allowed the identification of components found in extracts from zooplankton faecal pellets and a marine surface sediment. This highly sensitive technique should prove valuable for pigment analysis in environmental studies.
Use of plasma desportion mass spectrometry for pesticide analysis: The s‐alkylaminotriazines
Authors: Bourcier S. , Hoppilliard Y. , Kargar T.
Published: May 2005

The 2‐substituted‐4, 6‐di‐(alkylamino)‐1,3,5‐triazines (s‐triazines) are well known pesticides. With the dramatic increase in usage patterns of pesticides, an urgent need has arisen to develop analytical techniques to assist in identification of such compounds. A comprehensive understanding of the major fragmentations of these molecules, after ionization, could aid in this task. The use of conventional ionization techniques such as electron impact or chemical ionization is limited because of the relatively low volatility of these compounds, or because of thermal limitations. Recently, there have been promising developments in desorption ionizaion techniques for analysis of thermolabile and low volatility compounds such as environmental compounds. Among these techniques, the desorption ionization technique called ‘plasma desorption’ (PD) leads to more informative mass spectra than those obtained with other ionization techniques. A systematic investigation of ion formation and decomposition processes of three families of 2‐X substituted‐s‐triazines (X = Cl, SCH3 and OCH3) under PD conditions is presented. Eight pesticides were studied in this work. The influence of the X and alkyl substituents on the fragmentation processes under PD conditions is investigated in detail. Specific molecular ions (adduct ion, substitution ions …) allow the differentiation of each family, while characteristic fragment ions lead to the identification of the 1,3,5‐triazine ring and/or of its substituents. The fragmentation processes are obtained by combining nominal masses of ions determined in positive‐ion mass spectra and metastable transitions of low internal energy ions. This study is extended to analysis of s‐triazine mixtures. The results obtained lead to the establishment of a desorption order of these compounds under PD conditions. The experimental results are supported by semi‐empirical molecular orbital calculations. Finally, the proton affinity of Ametryn (2‐methylthio‐4‐(isopropylamino)‐6‐(ethylamino)‐s‐triazine) was determined to be close to that of histidine i.e. 970 kJ/mol.
Mass spectrometry of derivatives of dicyclopentadienyltitanium dichloride I. Behavior in electron impact ionization mass spectrometry
Authors: Wang Fu , Fang Ming , Wu Wannian , Chen Xuehua , Huang Jielin
Published: May 2005

Electron impact (EI) mass spectra of ten derivatives of dicyclopentadienyltitanium (IV) dichloride were studied. Fragmentation pathways were constructed and confirmed using daughter‐ion, parent‐ion and neutral‐species loss scan modes of MS/MS.
Characterization of over‐the‐counter cough/cold medications by liquid chromatography/electrospray mass spectrometry
Authors: Josephs Jonathan L.
Published: May 2005

Electrospray ioniztion (ESI) high‐performance liquid chromatography/mass spectrometry (LC/MS) has been utilized for the characterization of the active ingredients in over‐the‐counter (OTC) cough and cold medications. The use of in‐source collision‐induced dissociation (CID) on a single quadrupole instrument produced spectra with characteristic fragment ions. The in‐source CID potential was rotated through different energies on alternate scans throughout the chromatographic run. The spectra across a given chromatographic peak were summed and averaged to give composite spectra which displayed molecular ions in addition to fragment ions, producing library searchable spectra of analytes with varying collisional stabilities, within a single chromatographic run. These spectra were then saved into a library which was created with the following OTC drugs, phenylpropanolamine, doxvlamine, pyrilamine, chlorpheniramine, brompheniramine, dextromethorphan, cyclizine, and clemastine. The active ingredients in commercial OTC remedies were detected and characterized using this created library. The method requires no derivatization and minimal sample preparation, is applicable to a range of analytes, and can be fully automated for multiple sample analyses.
Analysis of tilmicosin in swine liver extracts by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry
Authors: Kiehl Douglas E. , Kennington Allison S.
Published: May 2005

Tilmicosin is a semisynthetic macrolide antibiotic used in the treatment of respiratory disease in cattle and swine. The technique of liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI‐MS) was employed in an on‐line capacity for the analysis of tilmicosin in extracts from spiked swine liver. Increasing the potential in the cone/skimmer region of the ion source resulted in an increased abundance of unique structurally indicating fragment ions of tilmicosin. Three ions, [M + H]+and two diagnostic fragment ions were chosen for confirmation of the presence of tilmicosin in swine liver tissue extracts using the mass spectrometer in selected‐ion monitoring mode. The ion abundance ratios arising from any given combination of ions in data acquired from extracts of swine liver tissue spiked with tilmicosin at 5 and 10 ppm were within <10% of the corresponding mean standard abundance ratio, and duplicate sample analyses exhibited < 10% relative standard deviation. These results suggest the potential for the application of LC/APCI‐MS as a confirmatory technique for tilmicosin in swine liver.
Massive cluster ablation as preparation for organic secondary ion imaging
Authors: Dookeran N. N. , McMahon J. M. , Short R. T. , Todd P. J.
Published: May 2005

A focused Cs+ beam was used to obtain secondary ion mass spectra and images from samples of stearic acid on gold before and after ablation by a beam of masive cluster ions. Ablation appears to have two effects on secondary ion emission. First, the number and intensity of peaks reflecting contamination are substantially reduced. Secondly, the absolute intensity of secondary ion current characteristic of the analyte increases. These features simplify mass spectra and improve contrast in the images obtained.
Chemical composition of wood casks for wine ageing as determined by pyrolysis/gc/ms
Authors: Galletti Guido C. , Carnacini Alberta , Bocchini Paola , Antonelli Andrea
Published: May 2005

Oak and chestnut cask staves were planed to a depth of one centimeter, collecting a sample every millimeter. The samples were ground and subjected to pyrolysis/gas chromatography/mass spectrometry in order to determine their composition. Thirty‐six compounds were identified, including a series of typical lignin phenolics commonly considered responsible for wine taste. All ions found in a previous pyrolysis/mass spectrometry study of oak wood and related to good quality whisky were confirmed in the mass spectra of the pyrolysis fragments specific for polysaccharides and lignin recorded in the present work. Compared to chestnut wood, oak wood showed significantly higher lignin and syringyl unit content and less variability as to lignin composition with depth.
High‐flow liquid chromatography/mass spectrometry interface using a parallel ion spray
Authors: Hiraoka K. , Fukasawa H. , Matsushita F. , Aizawa K.
Published: May 2005

By positioning the capillary of the ion spray parallel to the ion sampling orifice, several advantages have been found compared to the conventional perpendicular ion spray, e.g., higher sensitivity, stable operation, practically no contamination of the ion sampling orifice, and higher liquid flow rates up to 4 mL/min. This is due to the fact that while the charged fine liquid droplets are deflected towards the ion sampling orifice, the larger liquid droplets with lower charge density are entrained in the nebulizer gas jet and they are carried away outside the ion sampling system. With higher liquid flow rates (e.g. ⩾500 μL/min), the start of corona discharge does not result in a drastic decrease in the signal intensities of ions originating from sample solution. In electrospray experiments, it has also been found that the parallel spray gives better performance than the perpendicular one.
Sequencing peptides without scanning the reflectron: Post‐source decay with a curved‐field reflectron time‐of‐flight mass spectrometer
Authors: Cordero Marcela M. , Cornish Timothy J. , Cotter Robert J. , Lys Ihor A.
Published: May 2005

A time‐of‐flight mass spectrometer has been developed using a reflectron in which the voltages placed on the lens elements correspond to a function describing the arc of a circle. This curved‐field reflectron enables acquisition of focused product‐ion mass spectra at a single reflectron voltage. In this paper, we present results from this instrument for the amino acid sequencing of several peptides and describe the method of mass calibration.
Comparison of the mass spectrometric behaviour of fluorinated ethers and sulphides
Authors: Favretto D. , D'Alpaos M. , Traldi P. , Bégué J. P. , Bonnet‐Delpon D. , Rock M. H.
Published: May 2005

The mass spectrometric behaviour of two pairs of fluorinated vinyl‐ and allyl‐ethers and thioethers has been studied in detail with the aid of metastable ion data and accurate mass measurements. Clear differences have been observed between the two sets of compounds; while for the ethers the McLafferty rearrangement with ethylene loss represents a highly favoured decomposition route, for the thioethers the loss of the ethyl radical is preferred. Some decomposition routes, common to all the compounds examined, suggest the presence of hydrogen atom bridging between carbon and fluorine atoms. Theoretical calculations have shown that such a quasi CHF structure is already present in the neutral molecule in its ground state.