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Molecular Ions (molecular + ion)

Distribution by Scientific Domains

Chemistry	92%
Life Sciences	4%
2 Other Domains	4%

Distribution within Chemistry

Mass Spectrometry	78%
General & Introductory Chemistry	4%
6 Other Subdomains	14%

Selected Abstracts

Molecular depth profiling of multilayer structures of organic semiconductor materials by secondary ion mass spectrometry with large argon cluster ion beams

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2009
Satoshi Ninomiya
In this study, we present molecular depth profiling of multilayer structures composed of organic semiconductor materials such as tris(8-hydroxyquinoline)aluminum (Alq3) and 4,4,-bis[N -(1-naphthyl)- N -phenylamino]biphenyl (NPD). Molecular ions produced from Alq3 and NPD were measured by linear-type time-of-flight (TOF) mass spectrometry under 5.5,keV Ar700 ion bombardment. The organic multilayer films were analyzed and etched with large Ar cluster ion beams, and the interfaces between the organic layers were clearly distinguished. The effect of temperature on the diffusion of these materials was also investigated by the depth profiling analysis with Ar cluster ion beams. The thermal diffusion behavior was found to depend on the specific materials, and the diffusion of Alq3 molecules was observed to start at a lower temperature than that of NPD molecules. These results prove the great potential of large gas cluster ion beams for molecular depth profiling of organic multilayer samples. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Gas phase behavior of radical cations of perfluoroalkyl-1,2,4-triazines: an experimental and theoretical study

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009
Gianluca Giorgi
Abstract Electron ionization mass spectrometry and low-energy collision-induced decomposition reactions occurring in a tridimensional ion trap, together with density functional theory (DFT) calculations on neutrals, even- and odd-electron cations, have been used to study the gas-phase ion chemistry of a series of perfluoroalkyl-1,2,4-triazines. Loss of oxygen, due to thermal degradation occurring before ionization, likely involving the hydroxylamino group, has been observed. Compounds having a carbonyl group at position 6 of the triazine ring fragment in the source by elimination of NO followed by HF or CO. The decomposition pathways occurring due to CID experiments have shown interesting features depending on the nature and structure of precursor ions. Most of them involve elimination of endocyclic atoms, thereby producing contraction of the original six-membered ring or formation of acyclic structures. DFT (B3LYP/6-31G(d,p)) calculations have been used for evaluating structure, stability and properties of neutral and ionic species involved in gas-phase processes. In particular, it has been calculated that in the molecular ion the unpaired electron is mainly located on the exocyclic nitrogen, while the positive charge is on the C(6) carbon atom. Copyright © 2009 John Wiley & Sons, Ltd. [source]

linear free energy relationships;

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2007
UB3LYP/6-31G(d
The substituent effect on the reactivity of the CN bond of molecular ions of 4-substituted N -(2-furylmethyl)anilines toward two dissociation pathways was studied. With this aim, six of these compounds were analyzed by mass spectrometry using electron ionization with energies between 7.8 and 69.9 eV. Also, the UB3LYP/6-31G (d,p) and UHF/6-31G (d, p) levels of theory were used to calculate the critical energies (reaction enthalpies at 0 K) of the processes that lead to the complementary ions [C5H5O]+ and [M , C5H5O]+, assuming structures that result from the heterolytic and homolytic CN bond cleavages of the molecular ions, respectively. A kinetic approach proposed in the 1960s was applied to the mass spectral data to obtain the relative rate coefficients for both dissociation channels from ratios of the peak intensities of these ions. Linear relationships were obtained between the logarithms of the relative rate coefficients and the calculated critical energies and other thermochemical properties, whose slopes showed to be conditioned by the energy provided to the compounds within the ion source. Moreover, it was found that the dissociation that leads to [C5H5O]+ is a process strongly dependent upon the electron withdrawing or donating properties of the substituent, favored by those factors that destabilize the molecular ion. On the contrary, the dissociation that leads to [M , C5H5O]+ is indifferent to the polar electronic effects of the substituent. The abundance of both products was governed by the rule of Stevenson,Audier, according to which the major ion is the one of less negative electronic affinity. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Xanthopterin in the Oriental Hornet (Vespa orientalis): Light Absorbance Is Increased with Maturation of Yellow Pigment Granules

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009
Marian Plotkin
The Oriental hornet bears both brown and yellow colors on its cuticle. The brown component is contributed by the pigment melanin, which is dispersed in the brown cuticle and provides protection against insolation, while the yellow-colored part contains within pockets in the cuticle granules possessing a yellow pigment. These yellow granules (YG) are formed about 2 days prior to eclosion of the imago, and their production continues for about 3 days posteclosion. Xanthopterin is the main component of the granule and lends it its yellow color. Xanthopterin produces a characteristic excitation/emission maximum at 386/456 nm. Characterization by use of mass spectrometry showed the compound to have a molecular ion of 179, as expected from xanthopterin. Spectroscopic examination of the absorption of an entire stripe of yellow cuticle in the course of its metamorphosis revealed that the absorption steadily increases throughout the process to a maximal level of absorption about 3 days posteclosion. In the absence of the YG, the cuticle is permeable to the passage of all wavelengths within the visible range and to the UV range (290,750 nm) in all age groups of hornets. The newly ecloded hornets depart the nest to engage in activities requiring exposure to insolation only as the process of granule formation terminates, namely, when the layer of YG in the cuticle suffices to absorb all the harmful UV radiation. [source]

Determination of triclosan metabolites by using in-source fragmentation from high-performance liquid chromatography/negative atmospheric pressure chemical ionization ion trap mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2010
Jian-lin Wu
Triclosan is a widely used broad-spectrum antibacterial agent that acts by specifically inhibiting enoyl,acyl carrier protein reductase. An in vitro metabolic study of triclosan was performed by using Sprague-Dawley (SD) rat liver S9 and microsome, while the invivo metabolism was investigated on SD rats. Twelve metabolites were identified by using in-source fragmentation from high-performance liquid chromatography/negative atmospheric pressure chemical ionization ion trap mass spectrometry (HPLC/APCI-ITMS) analysis. Compared to electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) that gave little fragmentation for triclosan and its metabolites, the in-source fragmentation under APCI provided intensive fragmentations for the structural identifications. The invitro metabolic rate of triclosan was quantitatively determined by using HPLC/ESI-ITMS with the monitoring of the selected triclosan molecular ion. The metabolism results indicated that glucuronidation and sulfonation were the major pathways of phase II metabolism and the hydroxylated products were the major phase I metabolites. Moreover, glucose, mercapturic acid and cysteine conjugates of triclosan were also observed in the urine samples of rats orally administrated with triclosan. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Electrospray ionization and atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry of antioxidants applied in lubricants,

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2009
Alexander Kassler
The aim of this study was to investigate the utility of ion trap mass spectrometry (ITMS) in combination with the two desorption/ionization methods, electrospray (ESI) and atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI), for the detection of antioxidants which are applied in lubricants. These experiments should form the base for future investigations of antioxidants in tribologically formed thin layers on the surface of frictional systems. Seventeen different antioxidants were selected out of the group of hindered phenolic and aromatic aminic compounds. Practically all antioxidants could be characterized by positive ion ESI- and AP-MALDI-ITMS, forming various types/species of molecular ions (e.g. [M]+., [M+H]+, [M+Na]+ or [M,2H+H]+). A few compounds could be analyzed by negative ion ESI-MS, too, but none by negative ion AP-MALDI-MS. The influence of target materials in AP-MALDI-MS (gold- and titanium nitride (TiN)-covered stainless steel, micro-diamond-covered hard metal, hand-polished and sand-blasted stainless steel targets) with respect to the molecular ion intensity and type of molecular ion of two selected antioxidants was evaluated. The surface properties are of particular interest because in friction tests different materials with different surface characteristics are used. However, the MS results indicate that optimal target surfaces have to be found for individual antioxidants in AP-MALDI-MS but in general smooth surfaces were superior to rough surfaces. Finally the gold-covered stainless steel MALDI target provided the best mass spectra and was selected for all the antioxidants investigated. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Structural characterization and identification of iridoid glycosides, saponins, phenolic acids and flavonoids in Flos Lonicerae Japonicae by a fast liquid chromatography method with diode-array detection and time-of-flight mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2009
Lian-Wen Qi
A fast liquid chromatography method with diode-array detection (DAD) and time-of-flight mass spectrometry (TOF-MS) has been developed for analysis of constituents in Flos Lonicerae Japonicae (FLJ), a traditional Chinese medicine derived from the flower bud of Lonicerajaponica. The chromatographic analytical time decreased to 25,min without sacrificing resolution using a column packed with 1.8-µm porous particles (4.6,×,50,mm), three times faster than the performance of conventional 5.0-µm columns (4.6,×,150,mm). Four major groups of compounds previously isolated from FLJ were structurally characterized by DAD-TOF-MS: iridoid glycosides showed maximum UV absorption at 240,nm; phenolic acids at 217, 242, and 326,nm; flavonoids at 255 and 355,nm; while saponins had no absorption. In electrospray ionization (ESI)-TOF-MS experiments, elimination of a glucose unit (162 Da), and successive losses of H2O, CH3OH and CO, were generally observed in iridoid glycosides; saponins were characterized by a series of identical aglycone ions; phenolic acids typically generated a base peak at [M,H,caffeoyl], by loss of a caffeic acid unit (162 Da) and several marked quinic acid moiety ions; cleavage of the glycosidic bond (loss of 162 or 308 Da), subsequent losses of H2O, CO, RDA and C-ring fragmentation were the most possible fragmentation pathways for flavonoids. By accurate mass measurements within 4,ppm error for each molecular ion and subsequent fragment ions, as well as the ,full mass spectral' information of TOF-MS, a total of 41 compounds including 13 iridoid glycosides, 11 phenolic acids, 7 saponins, and 10 flavonoids were identified in a methanolic extract of FLJ. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Can density functional theory (DFT) be used as an aid to a deeper understanding of tandem mass spectrometric fragmentation pathways?

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2009
Alexander Alex
Prediction of tandem mass spectrometric (MS/MS) fragmentation for non-peptidic molecules based on structure is of immense interest to the mass spectrometrist. If a reliable approach to MS/MS prediction could be achieved its impact within the pharmaceutical industry could be immense. Many publications have stressed that the fragmentation of a molecular ion or protonated molecule is a complex process that depends on many parameters, making prediction difficult. Commercial prediction software relies on a collection of general heuristic rules of fragmentation, which involve cleaving every bond in the structure to produce a list of ,expected' masses which can be compared with the experimental data. These approaches do not take into account the thermodynamic or molecular orbital effects that impact on the molecule at the point of protonation which could influence the potential sites of bond cleavage based on the structural motif. A series of compounds have been studied by examining the experimentally derived high-resolution MS/MS data and comparing it with the in silico modelling of the neutral and protonated structures. The effect that protonation at specific sites can have on the bond lengths has also been determined. We have calculated the thermodynamically most stable protonated species and have observed how that information can help predict the cleavage site for that ion. The data have shown that this use of in silico techniques could be a possible way to predict MS/MS spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Cluster ion beam profiling of organics by secondary ion mass spectrometry , does sodium affect the molecular ion intensity at interfaces?

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008
Felicia M. Green
The use of cluster ion beam sputtering for depth profiling organic materials is of growing technological importance and is a very active area of research. At the 44th IUVSTA Workshop on "Sputtering and Ion Emission by Cluster Ion Beams", recent results were presented of a cluster ion beam depth profile of a thin organic molecular layer on a silicon wafer substrate. Those data showed that the intensity of molecular secondary ions is observed to increase at the interface and this was explained in terms of the higher stopping power in the substrate and a consequently higher sputtering yield and even higher secondary ion molecular sputtering yield. An alternative hypothesis was postulated in the workshop discussion which may be paraphrased as: "under primary ion bombardment of an organic layer, mobile ions such as sodium may migrate to the interface with the inorganic substrate and this enhancement of the sodium concentration increases the ionisation probability, so increasing the molecular ion yield observed at the interface". It is important to understand if measurement artefacts occur at interfaces for quantification as these are of great technological relevance , for example, the concentration of drug in a drug delivery system. Here, we evaluate the above hypothesis using a sample that exhibits regions of high and low sodium concentration at both the organic surface and the interface with the silicon wafer substrate. There is no evidence to support the hypothesis that the probability of molecular secondary ion ionisation is related to the sodium concentration at these levels. © Crown copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source]

The characterization of selected drugs with infrared laser desorption/tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2008
Yang Pan
Some selected drugs including captopril, fudosteine and racecadotril have been analyzed by infrared (IR) laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS). The molecular ions of captopril and racecadotril are exclusively observed without any fragments at near threshold single-photon ionization (SPI). However, fudosteine easily forms fragments even at a photon energy near the ionization threshold, indicating the instability of its molecular ion. For these drugs, a number of fragments are yielded with the increase of photon energy. The structures of such fragments proposed by IR LD/VUV PIMS are supported by electron ionization time-of-flight mass spectrometry (EI-TOFMS) results. Fragmentation pathways are discussed in detail. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Electron ionization mass spectral fragmentation of cholestane-3,,4,,5, -triol and cholestane-3,,5,,6,/, -triol bis- and tris-trimethylsilyl derivatives

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2005
J.-F. Rontani
The electron ionization (EI) mass spectral fragmentation of the bis- and tris-trimethylsilyl derivatives of cholestane-3,,4,,5, -triol, cholestane-3,,5,,6, -triol and cholestane-3,,5,,6, -triol was investigated. The EI mass spectrum of the 3,,4, -bis-trimethylsilyl derivative of cholestane-3,,4,,5, -triol exhibits interesting fragment ions at m/z 142 and 332 resulting from the initial loss of TMSOH between the carbons 2 and 3 and subsequent retro-Diels-Alder (RDA) cleavage of the ring A. Trimethylsilyl transfer between the 4, - and the 5, -hydroxy groups acts significantly before RDA cleavage affording an ion at m/z 404. Complete silylation of cholestane-3,,4,,5, -triol strongly stabilizes the molecule, affording an abundant molecular ion at m/z 636 and decreasing the abundance of the RDA cleavage. Loss of water (from the non-silylated 5, -hydroxy group) plays a very important role during the decomposition of the molecular ion of 3,,6,/, -bis-trimethylsilyl derivatives of cholestane-3,,5,,6,/, -triols. These derivatives appear to be very useful in assigning the configuration of the carbon 6. This assignment is based on the abundance of the fragment ions at m/z 321, 367 and 403, which are more prominent in the EI mass spectrum of the , -isomer. In contrast, EI mass spectra of the tris-trimethylsilyl derivatives of cholestane-3,,5,,6, -triol and cholestane-3,,5,,6, -triol differ only slightly and appear to be poorly informative. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Isomer differentiation by combining gas chromatography, selective self-ion/molecule reactions and tandem mass spectrometry in an ion trap mass spectrometer

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2003
Hui-Fen Wu
This study presents a novel, simple and rapid procedure for isomer differentiation by combining gas chromatography (GC), a selective self-ion/molecule reaction (SSIMR) and tandem mass spectrometry (MS/MS) in an ion trap mass spectrometer (ITMS). SSIMR product ions were produced from four isomers. For aniline, SSIMR induces the formation of the molecular ion, [M+H]+, [M+CH]+, adduct ions of fragments ([M+F]+, where F represents fragment ions) and [2MH]+. 2 and 3-Picoline produce [M+H]+, [2MH]+ and [M+F]+, while 5-hexynenitrile produces [M+H]+, [M+F]+ and [2M+H]+ ions. The proposed method provides a relatively easy, rapid and efficient means of isomer differentiation via a SSIMR in the ITMS. Typically, isomer differentiation can be achieved within several minutes. The superiority of the SSIMR technique for isomer differentiation over electronic ionization (EI) is also demonstrated. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Identification of 1-hydroxypyrene glucuronide in tissue of marine polychaete Nereis diversicolor by liquid chromatography/ion trap multiple mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2002
Anders M. B. Giessing
1-Hydroxypyrene glucuronide is identified as the single major aqueous metabolite of the tetracyclic aromatic hydrocarbon pyrene, in tissue from a deposit-feeding marine polychaete, Nereis diversicolor. Identification was performed using an ion trap mass spectrometer fitted with an atmospheric pressure chemical ionization (APCI) probe and connected to a high-performance liquid chromatography/diode array detector (HPLC/DAD) system. Besides 1-hydroxypyrene, the 339-nm UV trace of tissue samples from pyrene-exposed worms showed only one dominant peak that could be related to pyrene metabolism. Negative APCI-MS of this supposed 1- hydroxypyrene conjugate gave a characteristic signal at m/z 429 corresponding to the molecular ion of 1-hydroxypyrene glucuronide plus eluent adducts ([M,,,H,+,2H2O],). Fragmentation pathways were studied by isolating the abundant ion at m/z 429 in the ion trap and performing multiple mass spectrometric experiments (MSn). The fragmentations observed were consistent with the proposed identification. Two low intensity LC peaks that could be related to pyrene metabolism by their DAD absorption spectra were also present in the 339-nm UV chromatogram of tissue samples. However, these peaks could not be identified by their mass spectra in negative ion mode due to ion suppression by very abundant co-eluting impurities. The present method shows that LC/MSn is a fast and useful analytical tool for identification of aqueous polycyclic aromatic hydrocarbon biotransformation products in samples from relatively small marine invertebrates with limited sample preparation. Copyright © 2002 John Wiley & Sons, Ltd. [source]

A method for the identification of the double-bond position of isomeric linear tetradecenols and related compounds based on mass spectra of dimethyl disulfide derivatives

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2002
Gu Yuan
A simple method is presented for calculation of the double-bond position in linear tetradecenols based on mass spectral data of dimethyl disulfide derivatives. In this approach, the m/z ratios of the molecular ion and of one (or both) of the two most abundant fragment ions were utilized to calculate the double-bond position, without the requirement to identify both fragment ions resulting from carbon-carbon cleavage across what was originally the double bond. The approach was tested with mass spectra of dimethyl disulfide derivatives of 12 isomeric tetradecenols, and the double-bond position in each isomer was successfully identified by this method. The method was shown to work also for the corresponding acetates. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Ion chemistry of chloroethanes in air at atmospheric pressure

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2001
Anna Nicoletti
Ion chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non-thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di-, tri- and tetrachloroethanes diluted in air (500,1500,ppm) at atmospheric pressure were investigated at 30,°C and at 300,°C. Spectral changes due to collisional activation of the ions achieved by increasing ,V, the potential difference between sampling and skimmer cones, are informative of structures and ion-molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C-C and C-Cl cleavages of the molecular ion, M+·, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1-dichloroethane and 1,1,2,2-tetrachloroethane, which give [M,,,H]+ and [M,,,HCl]+· species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing ,V, the [M,,,HCl]+· ion formed from 1,1,2,2-tetrachloroethane undergoes the same fragmentation and ion-molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl, and its ion-neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X,)(M)n where X, is a background ion of the APCI plasma, namely O2,,O3, and, in some cases, (NO)2,. Peculiar to 1,1,1-trichloroethane are species attributed to Cl, complexes with phosgene, (Cl,)(Cl2C=O)n(n,=,1,2). Such complexes, which were not observed for either the isomeric 1,1,2-trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona-induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl,)(Cl2C=O)n and (Cl,)(M)n happen to be isobaric. Copyright © 2001 John Wiley & Sons, Ltd. [source]

On the Chemical Reaction of Matter with Antimatter

CHEMPHYSCHEM, Issue 8 2007
Evandro Lodi Rizzini Prof.
Abstract A chemical reaction between the building block antiatomic nucleus, the antiproton (p, or in chemical notation), and the hydrogen molecular ion () has been observed by the ATHENA collaboration at CERN. The charged pair interact via the long-range Coulomb force in the environment of a Penning trap which is purpose-built to observe antiproton interactions. The net result of the very low energy collision of the pair is the creation of an antiproton,proton bound state, known as protonium (Pn), together with the liberation of a hydrogen atom. The Pn is formed in a highly excited, metastable, state with a lifetime against annihilation of around 1 ,s. Effects are observed related to the temperature of the prior to the interaction, and this is discussed herein. [source]

High-Resolution LA-ICP-MS for Accurate Determination of Low Abundances of K, Sc and Other Trace Elements in Geological Samples

GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2010
Julia Regnery
LA-ICP-MS; haute résolution de masses; matériaux géologiques de référence; verres MPI-DING Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine K, Sc, Ti, V, Cr, Mn, Co, Ni and Zn in geological samples. Because the isotopes of these elements and the internal standard element (Ca) often have interferences from molecular ions when determined using quadrupole or sector-field ICP-MS in low mass resolution mode, ion intensities were measured at a high mass resolution of 4000. We investigated dynamic element fractionation, type and abundance of molecular ions using different geological reference materials. Highly resolved mass spectra were especially important for accurate low-abundance measurements. As a result, maximum "critical" concentration limits for each isotope were obtained, where a mass resolution of 4000 was necessary for reliable LA-ICP-MS analysis. To test the LA-ICP-MS technique, different international reference material glasses and powdered rock reference materials were analysed. Rock powders were fused to glass beads using an Ir-strip heater. Nearly all concentration values for the reference materials agreed with the reference values at the 95% confidence level. To demonstrate routine LA-ICP-MS analysis at a mass resolution of 4000, trace element data for Hawaiian basalts are also presented. La technique de spectrométrie de masse couplée à un plasma inductif et associée à un système d'ablation laser (LA-ICP-MS) a été utilisée pour la détermination des concentrations en K, Sc, Ti, V, Cr, Mn, Co, Ni and Zn dans des échantillons géologiques. Parce que les isotopes de ces éléments et l'élément utilisé comme standard interne (Ca) ont souvent des interférences liées à la formation d'ions moléculaires lorsqu'ils sont analysés par les techniques d'ICP-MS quadripolaire ou à secteur magnétique en mode basse résolution de masses, les intensités des ions ont été mesurées en mode haute résolution de masses de 4000. Nous avons étudié le fractionnement dynamique des éléments, le type et l'abondance des ions moléculaires en utilisant différents matériaux géologiques de référence. Les spectres de masse de haute résolution ont été particulièrement importants pour les mesures précises des faibles abondances. En conséquence, les limites maximales de concentration critique pour chaque isotope ont été obtenues, dans les cas où une résolution de masse de 4000 était nécessaire pour obtenir des analyses LA-ICP-MS fiables. Pour tester la technique LA-ICP-MS proposée, différents verres et poudres de matériaux de référence internationaux ont été analysés. Les poudres de roche ont été transformées en billes de verre par fusion dans un four automatique à chauffage par filament d'iridium. Presque toutes les concentrations obtenues pour les matériaux de référence sont en accord avec les valeurs de référence de la littérature à un niveau de confiance de 95%. Pour démontrer que la méthode présentée de LA-ICP-MS à résolution de masses de 4000 peut s'utiliser en routine, nous présentons également des données d'éléments traces de basaltes Hawaïens. [source]

Myth and Reality in the Attitude toward Valence-Bond (VB) Theory: Are Its ,Failures' Real?

HELVETICA CHIMICA ACTA, Issue 4 2003
Sason Shaik
According to common wisdom propagated in textbooks and papers, valence-bond (VB) theory fails and makes predictions in contradiction with experiment. Four iconic ,failures' are: a) the wrong prediction of the ground state of the O2 molecule, b) the failure to predict the properties of cyclobutadiene (CBD) viz. those of benzene, c) the failure to predict the aromaticity/anti-aromaticity of molecular ions like C5H and C5H, C3H and C3H, C7H and C7H, etc; and d) the failure to predict that, e.g., CH4 has two different ionization potentials. This paper analyzes the origins of these ,failures' and shows that two of them (stated in a and d) are myths of unclear origins, while the other two originate in misuse of an oversimplified version of VB theory, i.e., simple resonance theory that merely enumerate resonance structures. It is demonstrated that, in each case, a properly used VB theory at a simple and portable level leads to correct predictions, as successful as those made by use of molecular-orbital (MO) theory. This notion of VB ,failure', which is traced back to the VB-MO rivalry, in the early days of quantum chemistry, should now be considered obsolete, unwarranted, and counterproductive. A modern chemist should know that there are two ways of describing electronic structure, which are not two contrasting theories, but rather two representations or two guises of the same reality. Their capabilities and insights into chemical problems are complementary, and the exclusion of any one of them undermines the intellectual heritage of chemistry. [source]

Use of LC,MS,MS for the rapid, specific and sensitive quality control measurement of carrier in a PET radioligand: [18F]FECNT

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2005
H. Umesha Shetty
Abstract In the production of radioligands for imaging low concentrations of target proteins (e.g. receptors or transporters) in human subjects with positron emission tomography, control of specific radioactivity is necessary for efficacy and safety. Such quality control requires a fast method to be available for measuring carrier (non-radioactive ligand) in each batch of radioligand, preceding its release for administration. Measurement is usually achieved with HPLC equipped with an ultraviolet (UV) absorbance detector. However, this method is not easily applicable to radioligands that have low UV extinction coefficients and are produced at high specific radioactivity, such as [18F] (2,-carbomethoxy-3,-(4-chlorophenyl)-8-(2-fluoroethyl)nortropane; [18F]FECNT). Here we describe a fast, specific and sensitive LC,MS,MS method for measuring carrier in [18F]FECNT preparations. Small samples of formulated [18F]FECNT plus an added internal standard (2,-carbomethoxy-3,-(4-chlorophenyl)-8-(n -propyl)nortropane; INTSTD) are rapidly eluted from a short reverse phase HPLC column into an MS probe. Following electrospray ionization, the molecular ions ([MH]+) of FECNT (m/z=326) and INTSTD (m/z=322) are isolated and energized for collision-induced dissociation. The product ions from FECNT (m/z=294) and INTSTD (m/z=290) are monitored selectively. The calibration curve for MS response is linear for FECNT concentrations in the range 2,20 pg/µl and suitable for reproducibly (RSD 5%) and rapidly (<3 min) measuring low concentrations of carrier in [18F]FECNT preparations. Copyright © 2005 John Wiley & Sons, Ltd. [source]

ESI+ MS/MS confirmation of canine ivermectin toxicity,

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2009
A. F. Lehner
Abstract Ivermectin is a semisynthetic macrocyclic lactone anthelmintic of the avermectin family derived from Streptomyces fermentation products. Avermectins are used as antiparasitic agents in domestic animals; although considered relatively safe, one must consider animal species, breed, weight, and age in dosage determinations. In January 2006, two canines were presented to the UK Livestock Disease Diagnostic Center after dying from suspected ivermectin overdoses [30,50 mg/kg body weight]. To confirm this clinical diagnosis we developed a rapid, sensitive semiquantitative ElectroSpray Ionization,Mass Spectrometry (ESI/MS) method for ivermectin in canine tissue samples. Pharmaceutical ivermectin contains two ivermectins differing by a single methyl group, and each compound forms interpretation-confounding adducts with tissue Na+ and K+ ions. We now report that ivermectin administration was clearly confirmed by comparison with standard and dosage forms of ivermectin, and simple proportionalities based on mass spectral intensity of respective molecular ions allowed semiquantitative estimates of injection site tissue concentrations of 20 and 40 µg/g tissue (wet weight) in these animals, consistent with the history of ivermectin administration and the clinical signs observed. There is a distinct need for both rapid detection and confirmation of toxic exposures in veterinary diagnostics, whether for interpretation of clinical cases antemortem or for forensic reasons postmortem. It is vital that interpreters of analytical results have appropriate guidance in the scientific literature and elsewhere so as to enable clear-cut answers. The method presented here is suitable for routine diagnostic work in that it allows rapid extraction of ivermectin from tissue samples, avoids the need for high-performance liquid chromatography and allows ready interpretation of the multiple ivermectin species seen by ESI+ MS/MS in samples originating from veterinary dosage forms. Copyright © 2008 John Wiley & Sons, Ltd. [source]

linear free energy relationships;

Coprecipitation with calcium hydroxide for determination of iron in fish otoliths by collision cell ICP-MS,

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2007
Stephanie L. Daniels
Abstract A method has been described for the determination of iron from fish otoliths containing high levels of calcium by collision cell technology (CCT) ICP-MS. Iron (Fe) in otolith solutions was quantitatively coprecipitated with small amounts of calcium hydroxide by adding 1.0 M sodium hydroxide solution. The performance of CCT-ICP-MS pressurized with He/H2 cell gas was investigated on the elimination of Ca-based spectral interferences at m/z 54, 56 and 57. Molecular ion interferences at m/z 54 and 56 were reduced by 2 orders of magnitude. However, the interferences at m/z 57 increased by the same amount in the presence of Ca in solutions owing to the formation of 40Ca16 OH+ through reactions with H2 in collision cell, indicating that 57Fe was not suitable for the determination of Fe from otoliths. Results for 56Fe suffered significantly from interferences of Ca-based molecular ions when the Ca concentration in solution exceeded 100 µg ml,1, for which matrix-matched calibration was required for accurate determination. CCT with the aid of He/H2 cell gas proved to be very effective in eliminating the interferences (40Ar14N+ and 40Ca14N+) at m/z 54. Presence of Ca up to 300 µg ml,1 had virtually no effect on the ion signals of 54Fe, which with low background signals, afforded accurate determination of Fe from otoliths by using aqueous external standards. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Balance of xanthophylls molecular and protonated molecular ions in electrospray ionization

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2005
Thais Guaratini
Abstract This paper reports the chemical evidence of the balance between radical molecular ions and protonatedmolecules of xanthophylls (an oxygen-containing carotenoid) with a conjugated ,-system (polyene) and oxygen as a heteroatom in ESI and HRESI mass spectrometry. The ionization energy of neutral xanthophylls was calculated by semi-empirical methods. The results were compared with those previously published for carotenoids and retinoids, which have also been shown in ESI-MS to form M+, and [M + H]+, respectively. This study demonstrates, for the first time, the correlation of an extended conjugation and the presence of oxygen in the formation and balance of M+, or [M + H]+ for the carotenoids, neoxanthin, lutein, violaxanthin and zeaxanthin. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Simultaneous determination of mono-, di- and tributyltin in environmental samples using isotope dilution gas chromatography mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2004
Giuseppe Centineo
Abstract The development of a rapid, precise and accurate speciation method for the simultaneous determination of mono-, di- and tributyltin in environmental samples is described. The method is based on using isotope dilution gas chromatography/mass spectrometry (GC/MS) with electron ionization, a widely used technique in routine testing laboratories. A mixed spike containing 119Sn-enriched monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) was used for the isotope dilution of the samples. Five molecular ions were monitored for each analyte, corresponding to the 116Sn, 117Sn, 118Sn, 119Sn and 120Sn isotopes. The detection at masses corresponding to 116Sn and 117Sn were used to correct for m + 1 and m + 2 contributions of 13C from the organic groups attached to the tin atom on the 118Sn, 119Sn and 120Sn masses with simple mathematical equations and the concentrations of the butyltin compounds were calculated based on the corrected 118Sn/119Sn and 120Sn/119Sn isotope ratios. The 119Sn-enriched multispecies spike was applied with satisfactory results to the simultaneous determination of MBT, DBT and TBT in three certified reference materials: two sediments, PACS-2 and BCR 646, and the mussel tissue CRM 477. The method was compared with a previously published GC/inductively coupled plasma MS isotope dilution procedure, developed in our laboratory, by injecting the same samples into both instruments. Comparable analytical results in terms of precision and accuracy are demonstrated for both atomic and molecular mass spectrometric detectors. Thus, reliable quantitative organotin speciation analysis can be achieved using the more widespread and inexpensive GC/MS instrument. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Metabolites of an orally active antimicrobial prodrug, 2,5-bis(4-amidinophenyl)furan-bis- O -methylamidoxime, identified by liquid chromatography/tandem mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2004
Lian Zhou
Abstract DB75 (2,5-bis(4-amidinophenyl)furan) is a promising antimicrobial agent against African trypanosomiasis and Pneumocystis carinii pneumonia. However, it suffers from poor oral activity in rodent models for both infections. In contrast, a novel prodrug of DB75, 2,5-bis(4-amidinophenyl)furan-bis- O -methylamidoxime (DB289), has excellent oral activity. DB289 is currently undergoing clinical investigation as a candidate drug to treat primary stage African trypanosomiasis and Pneumocystis carinii pneumonia. In this study, metabolites of DB289 formed after incubation with freshly isolated rat hepatocytes were characterized using liquid chromatography/ion trap mass spectrometry. Administration of DB289 and octadeuterated DB289 in a 1 : 1 mixture greatly facilitated metabolite identification by providing isotope patterns with twin ions separated by 8 m/z units in the ratio 1 : 1, in the extracted ion chromatograms of molecular ions and in the product ion mass spectra of metabolites. Ten metabolites were identified. Series of O -demethylations and N -dehydroxylations led to the metabolic activation of DB289 to DB75 with the production of four intermediate phase I metabolites. Phase II glucuronidation and sulfation led to the formation of four glucuronide and one sulfate metabolites. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Formation of cryptophanes from their precursors as viewed by liquid secondary ion mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2001
Thierry Brotin
Abstract The formation of cryptophane-A (C1) and the deuterated cryptophanes C2,C6 from their respective precursors P1,P6 in a mass spectrometer ion-source was evidenced by liquid secondary ion mass spectrometry (LSIMS). Mass-analyzed ion kinetic energy experiments performed on the precursor molecular ions suggested that cryptophane formation occurred mainly in the liquid-matrix before desorption rather than in the gas phase. In addition, we observed that the presence of cations, such as lithium or sodium ions, inhibited the formation of the cryptophane molecular ions. In the light of these results we used the LSIMS technique to investigate the formation of the new cryptophanes C7,C13. All the data collected support the idea that a direct comparison can be made between these experimental findings and chemistry in solution. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Metastable ion study of organosilicon compounds.

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2001
(CH3)2Si(OCH3), CH3SiH(OCH3), Part XIII: dimethoxydimethylsilane, dimethoxymethylsilane
Abstract Unimolecular metastable fragmentations of dimethoxydimethylsilane, (CH3)2Si(OCH3)2 (MW 120, 1), and dimethoxymethylsilane, CH3SiH(OCH3)2 (MW 106, 2), upon electron impact ionization have been studied by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and the D-labeling technique in conjunction with thermochemistry. The results have been compared with those of the corresponding carbon analogues, 2,2-dimethoxypropane, (CH3)2C(OCH3)2 (MW 104, 3) and 1,1-dimethoxyethane, CH3CH(OCH3)2 (MW 90, 4). In analogy with the cases of 3 and 4, both molecular ions from 1 and 2 are formed at very low abundance at 70 eV, and begin to decompose by the expulsion of the substituents (H, CH3 or OCH3) on the central silicon atom. These decompositions are followed by the loss of a formaldehyde molecule (CH2O), as commonly observed in the mass spectra of methoxysilanes. Further, an ethylene (C2H4) or a dimethyl ether (CH3OCH3) molecule loss is observed in the fragmentation of some intermediate ions generated from 1+· and 2+·, but the mechanisms are different than those in the cases of 3 and 4. Some of these fragmentations are also different than those reported previously. The relative abundance of the ions in many MIKE spectra is explained by the extension of the Stevenson,Audier rule. The reaction, which is in contrast to the rule, however, is rationalized by the energy of the transition state for the reaction, estimated by semi-empirical molecular orbital calculation. The peak at m/z 59 from 2+· consists only of CH3OSi+ ion, whereas the peak from 1+· consists of two different ions, CH3OSi+ and (CH3)2Si+H. The ions CH3OSi+ from 1+· and 2+· are generated by at least two and three separate routes respectively. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Peptidergic modulation of male sexual behavior in Lymnaea stagnalis: structural and functional characterization of ,FVamide neuropeptides

JOURNAL OF NEUROCHEMISTRY, Issue 5 2003
A. B. Smit
Abstract In the simultaneous hermaphrodite snail Lymnaea stagnalis, copulation as a male is controlled by neurons that send axons to the male copulatory organs via a single penis nerve. Using direct mass spectrometry of a penis nerve sample, we show that one of the molecular ions has a mass corresponding to GAPRFVamide, previously identified from the buccal ganglia, and named Lymnaea inhibitory peptide (LIP). The identity of this peptide is confirmed by partial peptide purification from the penis nerve, followed by post source decay mass spectrometry. We cloned the LIP-encoding cDNA, which predicts a prohormone that gives rise to five copies of LIP (now re-named LIP A), two other ,FVamide peptides (LIPs B and C), and five structurally unrelated peptides. The LIP gene is expressed in neurons of the right cerebral ventral lobe that send their axons into the penis nerve. We show that the LIP A peptide is present in these neurons and in the penis nerve, and confirmed the presence of LIP B and C in the penis nerve by post source decay mass spectrometry. Finally, we demonstrate that LIP A, B and C inhibit the contractions of the penis retractor muscle, thereby implicating their role in male copulation behavior. [source]

Investigation of cis/trans ratios of peptide bonds in AVP analogues containing N -methylphenylalanine enantiomers

JOURNAL OF PEPTIDE SCIENCE, Issue 1 2006
Emilia Sikorska
Abstract The solution conformation of vasopressin analogues, modified at positions 2 and 3 with N -methylphenylalanine or its enantiomer, [D -MePhe2,MePhe3]AVP and [MePhe2,D -MePhe3]AVP, were studied by 2D NMR spectroscopy in H2O/D2O and theoretical calculations (EDMC/ANALYZE). In the case of [MePhe2,D -MePhe3]AVP, the synthesis afforded two products, A and B, which had identical molecular ions and similar retention times on HPLC. This finding was explained by racemization of Cys1, which gave an additional analogue, [D -Cys1,MePhe2,D -MePhe3]AVP (B). The possibility is not excluded of racemization of Cys1 in the remaining analogues of this series. However, only in the case of [MePhe2,D -MePhe3]AVP was this process so distinct that two strong peaks in the HPLC chromatogram were observed. The NMR spectra of all the analogues showed several distinct sets of residual proton resonances. This suggests that the peptides adopt more than two groups of conformations in H2O/D2O. This fact is due to cis/trans isomerization. Two more populated isomers arise from the cis/trans isomerization across the 2,3 peptide bond in [D -MePhe2,MePhe3]AVP and [MePhe2,D -MePhe3]AVP (A) and across the 1,2 peptide bond in [D -Cys1,MePhe2,D -MePhe3]AVP (B). Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. [source]

Increased vigabatrin entry into the brain by polysorbate 80 and sodium caprate

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 2 2001
D. Dimitrijevic
The effects of a non-ionic surfactant, polysorbate 80, and the sodium salt of the saturated fatty acid, sodium caprate (C10), as potential brain absorption enhancers for vigabatrin were studied. Vigabatrin is an enzyme-activated irreversible inhibitor of ,-aminobutyric acid (GABA) transaminase that increases brain and cerebrospinal GABA concentrations in animals and man. Before intravenous administration, a range of concentrations of the surfactants were tested using erythrocyte lysis or the red blood cell lysis test to establish the non-toxic concentration range. Vigabatrin was dissolved in 0.1% polysorbate 80 and 0.1% sodium caprate and administered intravenously in doses of 4 mL kg,1 to male Wistar rats (230,250 g; n = 3). Rats were killed 2 h after drug and surfactant administration and the brains were immediately removed and homogenized in 0.4m perchloric acid. Selected ion monitoring electrospray mass spectrometry was used to determine the concentration of vigabatrin and GABA directly from the perchloric acid extract of the rat brain. This method was developed to increase the speed and efficiency of the analysis by removing the need for complex extraction and derivatization procedures while retaining the specificity of the mass spectrometer as a detector. The stability of both vigabatrin and GABA in perchloric acid was established by monitoring their pseudo molecular ions in standard solutions at timed intervals over 24 h. Although the detection level for vigabatrin and GABA was at least 50 pg, only GABA was detected in rat brain. Vigabatrin caused a small increase in whole brain GABA. However, GABA levels were higher in the samples with vigabatrin + enhancer than in the samples where vigabatrin alone was administered. One-way analysis of variance indicated a significant effect of the surfactants on GABA levels (F (5,17) = 11.86, P < 0.01) and vigabatrin absorption was presumed. The rectal temperature of the rats is lowered by the presence of vigabatrin in the brain. Vigabatrin alone decreased rectal temperature by 6%. When given with either polysorbate 80 or sodium caprate, the extent of temperature lowering was significantly greater (P < 0.001). There was no significant difference after 2 h between polysorbate 80 + vigabatrin, and sodium caprate + vigabatrin. [source]