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Negative Ions (negative + ion)

Distribution by Scientific Domains

Chemistry	77%
Polymers and Materials Science	11%
Physics and Astronomy	7%

Terms modified by Negative Ions

negative ion mass spectrometry

negative ion mode

Selected Abstracts

Negative ion ,chip-based' nanospray tandem mass spectrometry for the analysis of flavonoids in glandular trichomes of Lychnophora ericoides Mart. (Asteraceae)

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2008
Leonardo Gobbo-Neto
This paper reports a method for the analysis of secondary metabolites stored in glandular trichomes, employing negative ion ,chip-based' nanospray tandem mass spectrometry. The analyses of glandular trichomes from Lychnophora ericoides, a plant endemic to the Brazilian ,cerrado' and used in traditional medicine as an anti-inflammatory and analgesic agent, led to the identification of five flavonoids (chrysin, pinocembrin, pinostrobin, pinobanksin and 3- O -acetylpinobanksin) by direct infusion of the extracts of glandular trichomes into the nanospray ionisation source. All the flavonoids have no oxidation at ring B, which resulted in a modification of the fragmentation pathways compared with that of the oxidised 3,4-dihydroflavonoids already described in the literature. The absence of the anti-inflammatory and antioxidant di- C -glucosylflavone vicenin-2, or any other flavonoid glycosides, in the glandular trichomes was also demonstrated. The use of the ,chip-based' nanospray QqTOF apparatus is a new fast and useful tool for the identification of secondary metabolites stored in the glandular trichomes, which can be useful for chemotaxonomic studies based on metabolites from glandular trichomes. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Development and validation of a ultra performance LC-ESI/MS method for analysis of metabolic phenotypes of healthy men in day and night urine samples

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 16-17 2008
Xijun Wang
Abstract Ultra-performance LC coupled to quadrupole TOF/MS (UPLC-QTOF/MS) in positive and negative ESI was developed and validated to analyze metabolite profiles for urine from healthy men during the day and at night. Data analysis using principal components analysis (PCA) revealed differences between metabolic phenotypes of urine in healthy men during the day and at night. Positive ions with mass-to-charge ratio (m/z) 310.24 (5.35 min), 286.24 (4.74 min) and 310.24 (5.63 min) were elevated in the urine from healthy men at night compared to that during the day. Negative ions elevated in day urine samples of healthy men included m/z 167.02 (0.66 min), 263.12 (2.55 min) and 191.03 (0.73 min), whilst ions m/z 212.01 (4.77 min) were at a lower concentration in urine of healthy men during the day compared to that at night. The ions m/z 212.01 (4.77 min), 191.03 (0.73 min) and 310.24 (5.35 min) preliminarily correspond to indoxyl sulfate, citric acid and N -acetylneuraminic acid, providing further support for an involvement of phenotypic difference in urine of healthy men in day and night samples, which may be associated with notably different activities of gut microbiota, velocity of tricarboxylic acid cycle and activity of sialic acid biosynthesis in healthy men as regulated by circadian rhythm of the mammalian bioclock. [source]

Ion Energy Distributions in Magnetron Sputtering of Zinc Aluminium Oxide

PLASMA PROCESSES AND POLYMERS, Issue S1 2009
Thomas Welzel
Abstract Ion energy distributions have been measured with an energy-dispersive mass spectrometer during magnetron sputtering of Al doped ZnO. A d.c. and a pulsed d.c. discharge have been investigated. Different positive ions from the target material have been observed with low energies in d.c. and a second energy peak of about 30 eV in pulsed d.c. with only weak additional energy due to the sputter process. Negative ions are mainly O, with energies corresponding to the target voltage of several 100 eV. They originate from the target and barely from the (O2) gas and hit the substrate opposite the race track. In pulsed d.c., due to the varying target voltage, energies of up to 500 eV have been observed. With increasing pressure, negative ions at the substrate are reduced exponentially in their density but not in their energy. [source]

The detection of phenotypic differences in the metabolic plasma profile of three strains of Zucker rats at 20 weeks of age using ultra-performance liquid chromatography/orthogonal acceleration time-of-flight mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2006
Robert S. Plumb
Analysis of biological fluids using ultra-performance liquid chromatography/mass spectrometry (UPLC/MS) (metabonomics) can allow new insights to be gained into disease processes, with advances in chromatographic techniques enabling the detection of thousands of metabolites. In this work metabonomics has been used to investigate the metabolic processes involved in type II diabetes in the Zucker obese rat. Plasma was analyzed from three different strains, the Zucker (fa/fa) obese, Zucker lean and the lean/(fa) obese cross. Using UPLC/MS, ca. 10,000 ions were detected due to the narrow peak widths and excellent peak shapes achieved with this technology. Confidence in the chromatographic performance was demonstrated by the use of quality control standards. The positive and negative ion total ion chromatograms obtained from the three strains were readily distinguishable using multivariate statistical analysis. The greatest difference was observed between the Zucker lean and Zucker lean/(fa) rats compared to the Zucker (fa/fa) obese rats. Positive ions m/z 220 (4.36,min), 282(3.78,min), 359 (5.33,min) and 405 (7.77,min) were elevated in the plasma derived from Zucker lean rats whilst ions m/z 385 (6.80,min) and 646 (4.36,min) were at a lower concentration compared to the plasma from the Zucker (fa/fa) obese animals. Negative ions elevated in the Zucker lean rats included m/z 212 (2.30,min), 514 (2.85,min), 295 (4.39,min), 329 (3.11,min), 343 (2.86,min) and 512 (2.86,min) with ions m/z 538 (4.18,min), 568 (4.18,min), 568 (5.09,min) and 612 (4.30,min) being raised in the samples derived from Zucker (fa/fa) obese animals. The ion m/z 514 (3.85,min) was found to correspond to taurocholate, providing further support for an involvement of taurine metabolism in diabetes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Characterization of ,- and ,-glutamyl dipeptides by negative ion collision-induced dissociation

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2004
Alex G. Harrison
Abstract The low-energy CID mass spectra of the [M , H], ions of a variety of dipeptides containing glutamic acid have been obtained using cone-voltage collisional activation. Dipeptides with the ,-linkage, H-Glu(Xxx-OH)-OH, are readily distinguished from those with the ,-linkage, H-Glu-Xxx-OH, by the much more prominent elimination of H-Xxx-OH from the [M , H], ions of the former isomers, resulting in formation of m/z 128, presumably deprotonated pyroglutamic acid. Dipeptides with the reverse linkage, H-Xxx-Glu-OH, show distinctive fragmentation reactions of the [M , H], ions including enhanced elimination of CO2 and formation of deprotonated glutamic acid. Exchange of the labile hydrogens for deuterium has shown that there is considerable interchange of C-bonded hydrogens with labile (N- and O-bonded) hydrogens prior to most fragmentation reactions. All dipeptides show loss of H2O from [M , H],. MS3 studies show that the [M , H , H2O], ion derived from H-Glu-Gly-OH has the structure of deprotonated pyroglutamylglycine while the [M , H , H2O], ions derived from H-Glu(Gly-OH)-OH and H-Gly-Glu-OH show a different fragmentation behaviour indicating distinct structures for the fragment ions. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Determination of 17,-estradiol in bovine plasma: development of a highly sensitive technique by ion trap gas chromatography,tandem mass spectrometry using negative chemical ionization,

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2002
Giancarlo Biancotto
Abstract A novel approach to the determination of 17,-estradiol in bovine plasma is presented. The observed enhanced sensitivity is gained by the application of tandem mass spectrometry (MS) fragmentation to a stable, well characterized negative ion produced by chemical ionization (methane as reagent gas). A specific derivatizing reactant is employed (pentafluorobenzyl bromide), combined with bis-trimethylsilyltrifluoroacetamide, to favor the formation of a diagnostic precursor negative ion. Plasma samples are purified through a C18 solid phase extraction column and derivatized before gas chromatography,MS analysis. The accuracy and the precision of the method, tested over a set of spiked samples, were satisfactory. The limit of detection was found to be 5 pg ml,1 and the limit of quantification was fixed at 20 pg ml,1. The fragmentation pattern is fully explained and the method is applicable for the official analysis of bovine plasma for the detection of 17,-estradiol according to the European criteria 256/93 and to the draft SANCO/1805/2000 rev. 3. The quantification of incurred positive samples was performed according to the proposed procedure and compared with the results obtained by standardized radio immuno assay; the estimated concentrations were significantly similar. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Negative ion ,chip-based' nanospray tandem mass spectrometry for the analysis of flavonoids in glandular trichomes of Lychnophora ericoides Mart. (Asteraceae)

Electrospray ionization mass spectrometry of AZT H -phosphonates conjugated with steroids

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2003
Qiang Xiao
AZT H -phosphonates conjugated with steroids were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated in detail. There are very different characteristic fragment ions in the positive and negative ion MS/MS spectra. The azide group of compounds 6a and 6b underwent either elimination of HN3 or rearrangement to an amine in both positive and negative ion mass spectrometry. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Phosphopeptide analysis by positive and negative ion matrix-assisted laser desorption/ionization mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2001
Katharina Janek
This article describes a simple procedure for the detection of phosphorylated peptides by comparable positive and negative ion mode matrix-assisted laser desorption/ionization mass spectrometry measurements. Based on studies with phosphorylated peptides (EAIXAAPFAK, X,=,pS, pT, pY) and their corresponding non-phosphorylated analogs, it was found that phosphopeptides, which are characterized by a low ionization efficiency in the positive ion mode, exhibit drastically increased signal intensities in the negative ion mode compared to their non-phosphorylated analogs. The effect was successfully used to identify phosphorylated sequences of the commonly used phosphoprotein standards, protein kinase A and ,-casein, by peptide mass fingerprint analyses of the corresponding Lys C and trypsin digests using both (positive and negative) ion modes. The comparison of positive and negative ion spectra of a given protein digest (relative intensity[M,,,H],/relative intensity[M,+,H]+) can be used to identify any phosphopeptides present which may then be separated and analyzed further. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A sensitive and specific liquid chromatography/tandem mass spectrometry method for determination of echinacoside and its pharmacokinetic application in rats

BIOMEDICAL CHROMATOGRAPHY, Issue 6 2009
Hao Yang
Abstract A rapid and sensitive method based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the determination of echinacoside in rat plasma was established and fully validated. A single step of liquid,liquid extraction with n -butanol was utilized. Chromatographic separation of the analyte and the internal standard (IS), chlorogenic acid, from the sample matrix was performed using a Capcell-MG C18 analytical column (100 2.0 mm × 5 µm), with a gradient of acetonitrile and water containing 0.1% acetic acid as the mobile phase. Detection was performed on a triple quadrupole tandem mass spectrometer equipped with electrospray ionization source operated in negative ion selected reaction monitoring mode. The method was linear in the concentration range 10,2500 ng/mL. The deviations of both intra- and inter-day precisions (RSD) were 7.1% and the assay accuracies were within 99.2,106.5%. Echinacoside proved to be stable during sample storage, preparation and analysis when an antioxidant solution was used. The method was successfully applied to a pharmacokinetic study in rats after an intragastric administration of echinacoside (100 mg/kg). With the lower limit of quantification at 10 ng/mL, this method proved to have sufficient selectivity, sensitivity and reproducibility for the pharmacokinetic study of echinacoside. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Determination of bergenin in human plasma after oral administration by HPLC-MS/MS method and its pharmacokinetic study

BIOMEDICAL CHROMATOGRAPHY, Issue 2 2009
Jin Wang
Abstract A highly sensitive, simple and selective high-performance liquid chromatography,tandem mass spectrometry (HPLC-MS/MS) method was developed and applied to the determination of bergenin concentration in human plasma. Bergenin and the internal standard (IS) thiamphenicol in plasma were extracted with ethyl acetate, separated on a C18 reversed-phase column, eluted with mobile phase of acetonitrile,water, ionized by negative ion pneumatically assisted electrospray and detected in the multi-reaction monitoring mode using precursor , product ions of m/z 327.1 , 192 for bergenin and 354 , 185.1 for the IS, respectively. The linear range of the calibration curve for bergenin was 0.25,60 ng mL,1, with the lowest limit of quantification of 0.25 ng mL,1, and the intra/inter-day relative standard deviation (RSD) was less than 10%. The method is suitable for the determination of low bergenin concentration in human plasma after therapeutic oral doses, and has been first and successfully used for its pharmacokinetic studies in healthy Chinese volunteers. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Quantitative LC/MS/MS method and in vivo pharmacokinetic studies of vitexin rhamnoside, a bioactive constituent on cardiovascular system from hawthorn

BIOMEDICAL CHROMATOGRAPHY, Issue 4 2007
Mingjin Liang
Abstract A simple and accurate liquid chromatography coupled with tandem mass spectrometry method was developed for determination and in vivo pharmacokinetic studies of vitexin rhamnoside in rat plasma. After protein precipitation using methanol, the analytes were separated by a Luna C18 column with an isocratic elution and analyzed by mass spectrometry in multiple reaction monitoring mode using the respective negative ion at m/z 577.2,293.0 for vitexin rhamnoside and m/z 593.2,413.0 for internal standard (IS) vitexin glucoside. The method was validated systematically within the concentration range 5,5000 µg/L (R > 0.996) and the lower limit of quantitation was 5 µg/L. Acceptable precision and accuracy were acquired for concentrations over the standard curve range. It was further applied to assess pharmacokinetics and bioavailability of vitexin rhamnoside after intravenous and oral administration to rats. The oral bioavailability of vitexin rhamnoside was only 3.57%, which indicated that vitexin rhamnoside had poor absorption or underwent extensive first-pass metabolism. Practical utility of this new LC/MS/MS method was confirmed in pilot pharmacokinetic studies in rats following both intravenous and oral administration. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Structure of d -3-hydroxybutyrate dehydrogenase prepared in the presence of the substrate d -3-hydroxybutyrate and NAD+

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2009
Md Mominul Hoque
d -3-Hydroxybutyrate dehydrogenase from Alcaligenes faecalis catalyzes the reversible conversion between d -3-hydroxybutyrate and acetoacetate. The enzyme was crystallized in the presence of the substrate d -3-hydroxybutyrate and the cofactor NAD+ at the optimum pH for the catalytic reaction. The structure, which was solved by X-ray crystallography, is isomorphous to that of the complex with the substrate analogue acetate. The product as well as the substrate molecule are accommodated well in the catalytic site. Their binding geometries suggest that the reversible reactions occur by shuttle movements of a hydrogen negative ion from the C3 atom of the substrate to the C4 atom of NAD+ and from the C4 atom of NADH to the C3 atom of the product. The reaction might be further coupled to the withdrawal of a proton from the hydroxyl group of the substrate by the ionized Tyr155 residue. These structural features strongly support the previously proposed reaction mechanism of d -3-hydroxybutyrate dehydrogenase, which was based on the acetate-bound complex structure. [source]

Comparison of Two Methods of Interpretation of LangmuirProbe Data for an Inductively Coupled Oxygen Plasma

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-6 2006
T. H. Chung
Abstract The Langmuir probe technique has some drawback in applying to electronegative plasma since it is difficult to interpret the probe I , V data. The positive ion flux to the probe is modified due to the presence of negative ions. In this study, an inductively coupled oxygen RF plasma is employed to perform the Langmuir probe measurement of the electronegative discharge. Plasma parameters are obtained from Langmuir probe measurement using two different methods which are based on electron energy distribution function (EEDF) integrals, and the method based on the fluid model for the modified ion flux, respectively. The EEDF is measured by a double differentiation of the I , V characteristics according to the Druyvesteyn formula. The electron densities estimated based on the two methods are compared. The EEDF integral method gives little higher values than the modified ion flux method. It is observed that at low pressure the EEDF is close to a Maxwellian. Generally, as the pressure increases, the distributions switch to bi-Maxwellian and to Druyvesteyn, and suggest some depletion of electrons with larger energies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Metastable anion fragmentations after resonant attachment: Deoxyribosic structures from quantum electron dynamics

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2008
I. Baccarelli
Abstract This work is focussed on the theoretical investigation of the observed fragmentation after the resonant electron attachment to gas-phase ,- D -deoxyribose. The collision energy of the incident electron is kept below 20 eV and both the furanosic and the pyranosic forms of the gaseous target are analyzed. All the transient negative ions associated to shape resonances are characterized in their energetics and spatial features, all pointing to highly selective bond-breaking resonant processes. The present results, when compared with the available experiments on gas-phase ,- D -deoxyribose and with the findings on the analogous conformers from the previously studied ,- D -ribose, offer new insights into the manifold fragmentation pathways occurring in biomolecules after electron attachment. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Studies of electron transfer dynamics in particle-surface interactions

ISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2005
Vladimir A. EsaulovArticle first published online: 10 MAR 2010
A review of recent work on electron transfer processes leading to neutralization of positive ions and formation of negative ions is presented. Experiments were performed on simple jellium-like metal surfaces, transition metals, and specific characteristics of electronic band structure were investigated for some cases, revealing differences in electron transfer processes between surfaces of the same element. It was shown that electronegative adsorbates like oxygen and chlorine provoke strong changes in electron transfer rates, which are akin to promotion and poisoning of reactions at surfaces. The results of experiments on Auger neutralization of He+ ions on Ag surfaces and H, and F, formation on Ag and Pd surfaces are presented and compared with recent theoretical treatments of these processes. The effect of adsorbates is illustrated by the example of chlorine adsorption on silver. Directions where further theoretical effort would considerably advance the understanding of these phenomena are delineated. [source]

Investigation of the postcure reaction and surface energy of epoxy resins using time-of-flight secondary ion mass spectrometry and contact-angle measurements

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009
Firas Awaja
Abstract Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate correlations between the molecular changes and postcuring reaction on the surface of a diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F based epoxy resin cured with two different amine-based hardeners. The aim of this work was to present a proof of concept that ToF-SIMS has the ability to provide information regarding the reaction steps, path, and mechanism for organic reactions in general and for epoxy resin curing and postcuring reactions in particular. Contact-angle measurements were taken for the cured and postcured epoxy resins to correlate changes in the surface energy with the molecular structure of the surface. Principal components analysis (PCA) of the ToF-SIMS positive spectra explained the variance in the molecular information, which was related to the resin curing and postcuring reactions with different hardeners and to the surface energy values. The first principal component captured information related to the chemical phenomena of the curing reaction path, branching, and network density based on changes in the relative ion density of the aliphatic hydrocarbon and the C7H7O+ positive ions. The second principal component captured information related to the difference in the surface energy, which was correlated to the difference in the relative intensity of the CxHyNz+ ions of the samples. PCA of the negative spectra provided insight into the extent of consumption of the hardener molecules in the curing and postcuring reactions of both systems based on the relative ion intensity of the nitrogen-containing negative ions and showed molecular correlations with the sample surface energy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

Theoretical studies on the electronic and optical properties of two new alternating fluorene/carbazole copolymers

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2005
Li Yang
Abstract Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)- co - alt -2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m = 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (,H-L), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (Egs) and the maximal absorption wavelength ,abs of PFmCz (m = 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as ,H-L, Eg, IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz)n series. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 969,979, 2005 [source]

Local existence for the one-dimensional Vlasov,Poisson system with infinite mass

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2007
Stephen Pankavich
Abstract A collisionless plasma is modelled by the Vlasov,Poisson system in one dimension. We consider the situation in which mobile negative ions balance a fixed background of positive charge, which is independent of space and time, as ,x, , ,. Thus, the total positive charge and the total negative charge are both infinite. Smooth solutions with appropriate asymptotic behaviour are shown to exist locally in time, and criteria for the continuation of these solutions are established. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Positron annihilation characteristics in UO2: for lattice and vacancy defects induced by electron irradiation

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
M.-F. Barthe
Abstract In this work both 22Na based positron lifetime spectroscopy (PALS) and slow positron beam based Doppler annihilation-ray broadening spectrometry (SPBDB) have been used to characterize respectively the bulk and the first micron under the surface of sintered UO2 disks that have been polished and annealed at high temperature (1700 °C/24 h/ArH2). Results show the presence of negative ions that are tentatively identified to negatively charged oxygen atoms located in interstitial sites. The positron annihilation characteristics in the UO2 lattice have been determined and are equal to SL(UO2) = 0.371(5), WL(UO2) = 0.078(7), ,L(UO2) = 169 ± 1 ps. Such disks have been irradiated at room temperature with electrons and , particles at different fluences. After irradiation SPBDB and PALS measurements show the formation of U-related vacancy defects after a 2.5 MeV electrons irradiation whereas no defects are detected for an irradiation at 1 MeV. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ion Energy Distributions in Magnetron Sputtering of Zinc Aluminium Oxide

The utility of ultra-performance liquid chromatography/electrospray ionisation time-of-flight mass spectrometry for multi-residue determination of pesticides in strawberry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2008
Michael J. Taylor
The utility of ultra-performance liquid chromatography/orthogonal-acceleration time-of flight mass spectrometry (UPLC/TOFMS) for the rapid qualitative and quantitative analysis of 100 pesticides targeted in strawberry was assessed by comparing results with those obtained using a validated in-house UPLC tandem mass spectrometry (MS/MS) multi-residue method. Crude extracts from retail strawberry samples received as part of the 2007 annual UK pesticide residues in food surveillance programme were screened for the presence of pesticide residues using UPLC/TOFMS. Accurate mass measurement of positive and negative ions allowed their extraction following ,full mass range data acquisition' with negligible interference from background or co-eluting species observed during UPLC gradient separation (in a cycle time of just 6.5,min per run). Extracted ion data was used to construct calibration curves and to detect and identify any incurred residues (i.e. pesticides incorporated in or on the test material following application during cultivation, harvest and storage). Calibration using matrix-matched standards was performed over a narrow concentration range of 0.005,0.04,mg,kg,1 with determination coefficients (r2) ,0.99 for all analytes with the exception of malathion/fenarimol/fludioxanil (r2,=,0.98), quassia/pymetrazine (r2,=,0.97) and fenthion sulfone (r2,=,0.95). Residues found in selected samples ranged from 0.025,0.28,mg,kg,1 and were in excellent agreement with results obtained using UPLC/MS/MS. Mass measurement accuracies of ,5,ppm were achieved consistently throughout the separation, mass range and concentration range of interest thus providing the opportunity to obtain discrete elemental compositions of target ions. © Crown copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source]

Method for the elucidation of the elemental composition of low molecular mass chemicals using exact masses of product ions and neutral losses: application to environmental chemicals measured by liquid chromatography with hybrid quadrupole/time-of-flight mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2005
Shigeru Suzuki
A method for elucidating the elemental compositions of low molecular weight chemicals, based primarily on mass measurements made using liquid chromatography (LC) with time-of-flight mass spectrometry (TOFMS) and quadrupole/time-of-flight mass spectrometry (LC/QTOFMS), was developed and tested for 113 chemicals of environmental interest with molecular masses up to ,400,Da. As the algorithm incorporating the method is not affected by differences in the instrument used, or by the ionization method and other ionization conditions, the method is useful not only for LC/TOFMS, but also for all kinds of mass spectra measured with higher accuracy and precision (uncertainties of a few mDa) employing all ionization methods and on-line separation techniques. The method involves calculating candidate compositions for intact ionized molecules (ionized forms of the sample molecule that have lost or gained no more than a proton, i.e., [M+H]+ or [M,H],) as well as for fragment ions and corresponding neutral losses, and eliminating those atomic compositions for the molecules that are inconsistent with the corresponding candidate compositions of fragment ions and neutral losses. Candidate compositions were calculated for the measured masses of the intact ionized molecules and of the fragment ions and corresponding neutral losses, using mass uncertainties of 2 and 5,mDa, respectively. Compositions proposed for the ionized molecule that did not correspond to the sum of the compositions of a candidate fragment ion and its corresponding neutral loss were discarded. One, 2,5, 6,10, 11,20, and >20 candidate compositions were found for 65%, 39%, 1%, 1%, and 0%, respectively, for the 124 ionized molecules formed from the 113 chemicals tested (both positive and negative ions were obtained from 11 of the chemicals). However, no candidate composition was found for 2% of the test cases (i.e., 3 chemicals), for each of which the measured mass of one of the product ions was in error by 5,6.7,mDa. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Phenol, chlorobenzene and chlorophenol isomers: resonant states and dissociative electron attachment,

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2003
Roustem V. Khatymov
This paper reports a study of resonant dissociative electron attachment (DEA) to the phenol, chlorobenzene, p- , m- , and o- chlorophenol molecules. On the basis of spectroscopic and thermochemical approaches the resonant states of the molecular negative ions (NIs) and the structures of some dissociative decay products are assigned. In the electron energy range up to 3,eV, DEA processes are determined by the two 2[,*]-shape resonances resulting mainly in formation of [MH], and/or Cl, ions. At higher electron energies the energy correlation between peaks in the negative ion effective yield curves and bands of UV spectra allowed identification of the core-excited resonances. The peculiarities of Cl, ion formation and the vibrational fine structure on the effective yield curves of the [MH], ions are discussed. The mass spectrometric procedures for measurement of relative cross sections for NI formation are described. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Vapor species over cerium and samarium trichlorides, enthalpies of formation of (LnCl3)n molecules and Cl,(LnCl3)n ions

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2001
A. M. Pogrebnoi
A Knudsen effusion cell mass spectrometric technique was used to study vapor species over CeCl3 and SmCl3. Monomer, dimer, and trimer (Sm3Cl9) molecules, and LnCl4,, Ln2Cl7,, Ln3Cl10, (Ln,=,Ce, Sm) negative ions, were observed in saturated vapor in the temperature range 958,1227,K. Partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation (,sH, 298,K, kJ·mol,1) to monomers and associated molecules obtained: 328,±,6 (CeCl3), 306,±,6 (SmCl3), 453,±,16 (Ce2Cl6), 408,±,12 (Sm2Cl6), and 468,±,40 (Sm3Cl9). Equilibrium constants for various chemical reactions were measured and the enthalpies of reactions obtained using the second and third laws of thermodynamics. The enthalpies of formation (,fH, 298,K, kJ·mol,1) of molecules and ions have been calculated as follows: ,730,±,6 (CeCl3), ,722,±,6 (SmCl3), ,1663,±,16 (Ce2Cl6), ,1649,±,13 (Sm2Cl6), ,2617,±,40 (Sm3Cl9), ,1250,±,15 (CeCl4,), ,1252,±,15 (SmCl4,), ,2184,±,35 (Ce2Cl7,), ,2172,±,26 (Sm2Cl7,), ,3183,±,43 (Ce3Cl10,), and ,3147,±,43 (Sm3Cl10,). Copyright © 2001 John Wiley & Sons, Ltd. [source]

Monellin (MNEI) at 1.15,Å resolution

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2007
J. R. Hobbs
The X-ray crystal structure of a single-chain monellin protein (MNEI) has been determined at 1.15,Å resolution. The model was refined to convergence employing anisotropic displacement parameters and riding H atoms to produce a final model with Rwork and Rfree values of 0.132 and 0.162, respectively. The crystal contains a single MNEI protein in the asymmetric unit and unusually lacks the dimer interface observed in all previous crystal structures of monellin and its single-chain derivatives. The high resolution allowed a more detailed view of MNEI than previously possible, with 38 of the 96 residues modelled with alternative side-chain conformations, including four core residues Thr12, Cys41, Leu62 and Ile75. Four stably bound negative ions were also located, providing new insight into potential electrostatic interactions of MNEI with the largely negatively charged surface of the sweet taste receptor T1R2,T1R3. [source]