Electron Impact Ionization

The use of mass spectra generated at 70 eV in electron ionization (EI) as a universal standard for EI has helped in the generation of searchable library databases and had a profound influence on the analytical applications of gas chromatography/mass spectrometry (GC/MS), similarly for liquid chromatography tandem mass spectrometry (LC-MS/MS), suggesting a novel method to normalize the collisional energy for the universalization of fragmentation energy for the analysis of Chemical Weapon Convention (CWC)-related chemicals by atmospheric pressure ionization-tandem mass spectrometry (API-MS n ) using threedimensional (3D) ion trap instruments. For normalizing fragmentation energy a "fragmentation energy index" (FEI) is proposed which is an arbitrary scale based on the fact of specific MS/MS fragmentation obtained at different collisional energies for the reference chemicals which are not CWC scheduled compounds. FEI 6 for the generation of an MS n librarysearchable mass spectral database is recommended.

We report the fabrication and experimental characterization of a carbon nanotube (CNT)-based MEMS/NEMS electron impact gas ionizer with an integrated extractor gate for portable mass spectrometry. The ionizer achieves low-voltage ionization using sparse forests of plasma-enhanced chemical-vapordeposited CNTs as field emitters and a proximal extractor grid with apertures aligned to the CNT forests to facilitate electron transmission. The extractor gate is integrated to the ionizer using a high-voltage MEMS packaging technology based on Si springs defined by deep reactive ion etching. The ionizer also includes a high-aspect-ratio silicon structure (μfoam) that facilitates sparse CNT growth and also enables uniform current emission. The devices were tested as field emitters in high vacuum (10 −8 torr) and as electron impact ionizers using argon at pressures of up to 21 mtorr. The experimental data show that the MEMS extractor gate transmits up to 66% of the emitted current and that the ionizers are able to produce up to 0.139 mA of ion current with up to 19% ionization efficiency while consuming 0.39 W. [2009-0246] Index Terms-Carbon nanotubes (CNTs), deep reactive ion etching (DRIE), electron impact ionization, field emission, gas ionizer, portable mass spectrometry (MS), 3-D MEMS packaging. I. INTRODUCTION M ASS SPECTROMETERS are powerful analytical tools that are helpful to quantitatively determine the chemical composition of a sample. Unfortunately, conventional mass spectrometry (MS) hardware is bulky and power hungry, which limits the range of applications that the technology can satisfy. The development of gas chromatography and MS (GC/MS) systems that are small, light, mechanically and thermally robust, and low-powered would enable their portability and therefore would expand the applicability of MS techniques. Portable GC/MS systems, either as individual units or as part of massive networks, can be used in a wide range of in situ applications including geological survey, law enforcement, environ-Manuscript

The electron gun plays an important role in atomic, molecular, and surface physics. Different types of electron guns have been designed for producing different electron beam energies. In this study, we present the modeling and construction of a seven-element electron gun with deflector system for electron impact studies. The electron optics of the electron gun was simulated and optimized using electron-beam ray-tracing simulation program SIMION 3D 7.0. Different operation mode of the gun, afocal, broad, and zoom beam mode, can be accommodated by adjusting various potentials. This modeling proposed here may help to design new types of electron guns and applications using cylinder and aperture lenses in collision experiments. r

We report results from high-resolution studies of D 5 + cluster ion collisions with low-energy electrons performed in a heavy ion storage ring. Absolute dissociative recombination (DR) and dissociative excitation (DE) cross sections were determined for the energy range from 0.0005 to 20 eV. The DR cross sections were exceedingly large at low energies, and DR resulted in efficient internal energy redistribution and pronounced fragmentation with two main product channels: D 2 + 3D (0.62 ± 0.03) and 2D 2 + D (0.35 ± 0.01). The DR and DE cross sections were comparable in the energy range from 0.2 to 20 eV, which suggest that the two processes follow similar dynamics and are competing outcomes of the ion-electron interaction. A simple picture of the recombination process of D 5 + which captures the essential physics is suggested.

The rare L-citronellal form of Backhousia citriodora F. Muell. was first reported in 1950 but attempts to relocate it were unsuccessful until 1996. The quest to relocate trees of this type has been driven by interest in L-citronellal for perfumery. The common, citral form of the species is already under cultivation for oil production in Australia. This paper reports on the rediscovery of the L-citronellal form, first in 1996 in a year-old provenance/progeny trial of B. citriodora in south-eastern Queensland, and then in a natural population on Queensland's Sunshine Coast in 1998. The three L-citronellal trees in the trial gave foliar oil concentrations (g/100 g dry weight) of 3.2, 2.2 and 1.8, respectively, when sampled in November 1996. The same trees sampled in March 1999 gave pale yellow oils consisting of 85-89% citronellal, 6-9% isopulegol isomers with small quantities of citronellol (approx. 3%) and several other compounds. Data on the physicochemical properties of these oils are given in the paper. Seed from a single mature L-citronellal tree gave progeny of both the L-citronellal and citral form in a ratio of approximately 1 : 1. Propagation material from many more plants of the L-citronellal form needs to be collected and assembled in breeding populations. This would form the basis of a selection and breeding programme, should this chemotype show economic potential.

The need for high]y charged heavy ions from projected particle accelerators has recently led to a re-evaluation of the complex processes of ion production in laser generated plasmas. Possible mechanisms for the production of intense beams of high charge state ions are investigated as is the experimental evidence for these mechanisms. The hypothesis that 20 keV ions are driven by "hot electrons" is not supported by experimental work to date. This work, on the other hand, suggests that 30ps pulsation is the basic mechanism for the acceleration of tantalum ions up fo charge state 8-t-whose energy increases linearly with charge state up to 24keV. For long pulses and charge states between 8-}-and 18n u, it appears that there is a secondary mechanism of electron impact ionisation by plasma electrons of approximately 200 eV in the plasma in front of the target, resulting in ions whose energy of around 24 keV is independent of charge state.

The effect of temperature in the 293-473 K range, on the secondary electron emission (SEE) yield of single crystal and polycrystalline diamond film surfaces is reported. For the polycrystalline films the SEE yield was found to decay as function of electron irradiation dose while for the single crystal an increase occurs first, followed by a decrease. For both surfaces, the

Dust grains are common in the space environment and being immersed in plasma, they become charged. It is well known that a motion of grains in space is driven mainly by electrodynamic forces and thus the grain charge is important for processes like the coagulation or dust cloud formations. Among other charging currents, emission processes are very important for setting the dust charge. It is believed that emission processes are connected exclusively with surface properties of dust grains but it is not evident for the surfaces covered by a very thin layer of different material (e.g., oxidized metal). For this reason, we investigate surface effects experimentally.

This paper investigates the mechanism of water splitting in photosystem II (PSII) as described by chemically sensible models of the oxygen-evolving complex (OEC) in the S0-S4 states. The reaction is the paradigm for engineering direct solar fuel production systems since it is driven by solar light and the catalyst involves inexpensive and abundant metals (calcium and manganese). Molecular models of the OEC Mn 3CaO4Mn catalytic cluster are constructed by explicitly considering the perturbational influence of the surrounding protein environment according to state-of-the-art quantum mechanics/molecular mechanics (QM/MM) hybrid methods, in conjunction with the X-ray diffraction (XRD) structure of PSII from the cyanobacterium Thermosynechococcus elongatus. The resulting models are validated through direct comparisons with high-resolution extended X-ray absorption fine structure spectroscopic data. Structures of the S3, S4, and S0 states include an additional µ-oxo bridge between Mn(3) and Mn , not present in XRD structures, found to be essential for the deprotonation of substrate water molecules. The structures of reaction intermediates suggest a detailed mechanism of dioxygen evolution based on changes in oxidization and protonation states and structural rearrangements of the oxomanganese cluster and surrounding water molecules. The catalytic reaction is consistent with substrate water molecules coordinated as terminal ligands to Mn(4) and calcium and requires the formation of an oxyl radical by deprotonation of the substrate water molecule ligated to Mn(4) and the accumulation of four oxidizing equivalents. The oxyl radical is susceptible to nucleophilic attack by a substrate water molecule initially coordinated to calcium and activated by two basic species, including CP43-R357 and the µ-oxo bridge between Mn(3) and Mn(4). The reaction is concerted with water ligand exchange, swapping the activated water by a water molecule in the second coordination shell of calcium. † Current address:

Gas chromatography/mass spectrometry (GC/MS) and enzyme-linked immunosorbent assay (ELISA) techniques were used to measure concentrations of dissolved atrazine in 149 surface-water samples. Samples were collected during May 1992-September 1993 near the mouth of the White River (Indiana) and in two small tributaries of the river. GC/MS was performed on a Hewlett-Packard 5971A t with electron impact ionization and selected ion monitoring of filtered water samples extracted by C-18 solid phase extraction; ELISA was performed with a magnetic-particle-based assay with photometric analysis. ELISA results compared reasonably well to GC/MS measurements at concentrations below the Maximum Contaminant Level for drinking water set by the U.S. Environmental Protection Agency (3.0 Ixg/L), but a systematic negative bias was observed at higher concentrations. When higher concentration samples were diluted into the linear range of calibration, the relation improved. A slight positive bias was seen in all of the ELISA data compared to the GC/MS results, and the bias could be partially explained by correcting the ELISA data for cross reactivity with other triazine herbicides. The highest concentrations of atrazine were found during the first major runoff event after the atrazine was applied. Concentrations decreased throughout the rest of the sampling period even though large runoff events occurred during this time, indicating that most atrazine loading to surface waters in the study area occurs within a few weeks after application. About 1.4 X 108 kg/yr of herbicides have been applied to farm land in the midwestern United States (Gianessi and Puffer 1991). Because many currently used herbicides are moderately water soluble (>30 mg/L) and have environmental half-lives

A gas chromatography-mass spectrometry (GC-MS) method has been proposed for the simultaneous determination of aliphatic and aromatic amines in indoor and outdoor air samples. The method includes pre-concentration of the compounds by percolating the air samples through the acidic solution, ion-pair extraction with bis-2-ethylhexylphosphate (BEHPA), derivatisation of compounds with isobutyl chloroformate (IBCF) and their GC-MS analysis. Aliphatic and aromatic amines were isolated from aqueous samples using BEHPA as ion-pair reagent and derivatised with IBCF for their chromatographic analysis. Aliphatic and aromatic amines were then analysed with GC-MS in both electron impact (EI) and positive and negative ion chemical ionisation (PNICI) mode as their isobutyloxycarbonyl (isoBOC) derivatives. The obtained recoveries ranged from 75.6 to 96.8% and the precision of this method, as indicated by the relative standard deviations (R.S.D.) was within the range of 1.0-4.4%. The detection limits obtained from calculations by using GC-MS results based on S/N: 3 were within the range of 0.08-0.01 ng/m 3 .

Differential and integral cross sections for elastic electron collisions with uracil, cytosine, guanine, adenine and thymine have been calculated using the independent atom method with a static-polarization model potential for incident energies ranging from 50 to 4000 eV. Total cross sections for single electron-impact ionization of selected DNA and RNA bases have also been calculated with the binary-encounter-Bethe model from the ionization threshold up to 5000 eV. Cross sections within the investigated energy range, can be related to the molecular symmetry, the number of target electrons and molecular size; elastic and ionization processes are most efficient for guanine and adenine molecules, while the lowest cross sections were obtained for the uracil molecule. The ionization cross sections for cytosine, thymine, adenine and guanine are compared with those recently obtained with a semi-classical and binary-encounter-Bethe formalisms. No theoretical and experimental data for elastic electron scattering from DNA and RNA bases are available, but comparisons with calculations for molecules of similar size and geometry allows the validity of the theoretical approach to be verified.

Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n 6 4 are treated individually, while the states with n P 5 are considered degenerate. For the processes involving transitions to and from n P 5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.

The importance of electron bremsstrahlung has continuously grown since its early discovery more than one century ago, increasingly being involved in different scientific areas. The present work deals with the prediction of thick-target bremsstrahlung spectrum in the frame of scanning electron microprobe analysis. X-ray energies considered range from 0.25 to 50 keV, whereas the models discussed involve electron incident energies up to 50 keV. The main attempts proposed to describe the thick target bremsstrahlung by electron impact are reviewed. Developments carried out from theoretical bases are considered, as well as the role played by Monte Carlo simulations. The results achieved by empirical models are particularly emphasized in view of their reliability in the description of the bremsstrahlung spectrum by means of analytical functions of the atomic number, beam energy and photon energy.

Vernonia galamensis is a new potential industrial oilseed crop found in tropical Africa. It is the source of a naturally epoxidized oil called vernonia oil (VO) which is extracted from the seed of the plant. In this study VO was used as the starting material for the synthesis of a mixture of amines, with the major product amine being N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amine. VO was transesterified via a base catalyzed methanolysis using sodium methoxide to yield VO methyl esters (VOME). Aminolysis of the VOME with dimethylamine as reagent and solvent under reflux conditions afforded the tertiary amides, with N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amide as the major product. The mixture was then subjected to metal hydride reduction with lithium aluminum hydride in diethylether under reflux conditions to obtain the desired amine mixture including N,N-dimethyl-(12S,13R)-epoxycis-9-octadecenyl amine. Electron impact mass spectrometry was used to characterize the mixture of amines. Additionally, proton NMR, 13 C NMR, and FTIR were used for characterization of N,N-dimethyl-(12S,13R)-epoxy-cis-9-octadecenyl amine. To further confirm the conversion of VO to the amines, the quaternary ammonium salts were synthesized and characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Continuous subcritical water extraction (CSWE) and hydrodistillation were compared for the extraction of essential oil from marjoram leaves. Ground marjoram leaves (0.4 g) were subjected to dynamic extraction with water at 50 bar, 1508C and 2 ml / min for 15 min. Hydrodistillation was performed treating 140 g of marjoram leaves with 1000 ml of water for 3 h. When CSWE was used the compounds were removed from the aqueous extract by a single extraction with 5 ml of hexane, detected by gas chromatography-flame ionization detection (GC-FID) and identified by mass spectrometry, electronic impact. The CSWE method is quicker (15 min versus 3 h), provides a more valuable essential oil (with higher amounts of oxygenated compounds and no significant presence of terpenes) and allows substantial savings of costs, in terms both of energy and plant material. The efficiency (in terms of volume of essential oil / 1 g of plant) of CSWE is 5.1 times higher than that provided by hydrodistillation. The precision of the overall method (CSWE combined with GC-FID) is good (RSD less than 7.5%) for n55.

Supercritical fluid extraction (SFE) represents an efficient and environmentally friendly technique for isolation of phytoconstituents from different plant sources. The present study is focused on extraction of flavonoids from Solanum melongena Linn fruit using Supercritical fluid (SCF-CO 2 ) technology. The fruit extract containing flavonoids has been reported to have hypolipidemic activity. The objective of this work is to evaluate the SCF extraction of flavonoid from S. melongena L. fruit at different operational conditions and discuss the temperature, pressure and flow rate of CO 2 dependence in the extract composition profile. Since Carbon dioxide is a non-polar solvent, ethanol is used as co-solvent to increase the polarity of the fluid. HPLC-PDA determination of flavonoids is done for each condition and the extraction conditions are optimized. Chromatographic conditions employed for determination of flavonoids component in fruit extract for PDA analysis are mobile phase (Methanol: Acetonitrile: Orthophosphoric acid: Acetic acid: Water, 200:100:10:10:200 v/v), at a flow rate of 1mL/min. The optimized SC-CO 2 extraction conditions under which maximum yields of flavonoids are obtained are temperature 45 0 C, Pressure 19.61MPa, co-solvent at 11.5% with a CO 2 flow rate 3.0mL/min. Further, in vitro free radical scavenging activity of SFE extract was evaluated by 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging method. Ascorbic acid was used as the reference. SFE extract exhibited promising antiradical effects in a concentration dependent manner. Linear regression analysis was used to calculate IC 50 value. Results showed that, the extract exhibited significant DPPH radical scavenging activity with IC 50 value of 66.063±0.15 µg/mL.

TECHNIQUES DE L'INGÉNIEUR L'expertise technique et scientifique de référence Techniques de l'Ingénieur p2645 Spectrométrie de masse-Principe et appareillage Date de publication : 12/09/2014 Par : Cet article fait partie de la base documentaire : Mesures-Analyses Dans le pack : Mesures-Analyses et dans l'univers : Technolgies de l'information

The class of fatty alcohol alkoxylates describes surfactants that are synthesised by reaction of fatty alcohols with alkoxides such as ethylene oxide or propylene oxide or a combination of both as copolymers. Such alkoxylates are used, for example, as nonionic surfactants in home and industrial cleaning and washing agents. Chemical characteristics of such alkoxylate copolymers, for example the degree of alkoxylation, the arrangement of building blocks (random or block polymerisation), the type of the starter, and endcapping, play an important role in application behaviour. The analysis of these characteristics is challenging because in many cases such copolymers have high polydispersity and a large number of constitutional isomers depending on the degree of alkoxylation. Furthermore, the alkoxylates often occur in a complex multicomponent matrix. Here we present a method for characterization of silylated fatty alcohol alkoxylates in the low-molecularweight range by means of comprehensive two-dimensional gas chromatography-mass spectrometry with electron impact and chemical ionisation. This method also enables detailed analysis of the alkoxylates in a complex matrix such as modern detergents.

Single-photon infrared emission spectroscopy (SPIRES) has been used to measure emission spectra from polycyclic aromatic hydrocarbons (PAHs). A supersonic free-jet expansion has been used to provide emission spectra of rotationally cold and vibrationally excited naphthalene and benzene. Under these conditions, the observed width of the 3.3-µm (C-H stretch) band resembles the bandwidths observed in experiments in which emission is observed from naphthalene with higher rotational energy. To obtain complete coverage of IR wavelengths relevant to the unidentified infrared bands (UIRs), UV laser-induced desorption was used to generate gas-phase highly excited PAHs. Lorentzian band shapes were convoluted with the monochromatorslit function in order to determine the widths of PAH emission bands under astrophysically relevant conditions. Bandwidths were also extracted from bands consisting of multiple normal modes blended together. These parameters are grouped according to the functional groups mostly involved in the vibration, and mean bandwidths are obtained. These bandwidths are larger than the widths of the corresponding UIR bands. However, when the comparison is limited to the largest PAHs studied, the bandwidths are slightly smaller than the corresponding UIR bands. These parameters can be used to model emission spectra from PAH cations and cations of larger PAHs, which are better candidate carriers of the UIRs.

First-order many-body theory has been used to calculate correlation and coherence parameters for the electron impact excitation of the 31P1 and 33P1 and states of neon. Both LS-coupled and spin-orbit-coupled results are reported for the 31P1 state. Calculations were completed for E=20, 30, 40, 50, 80, 100 and 120 eV electron impact energies. Theoretical results are compared with those that

Essential oils from Hyptis suaveolens (L.) Poiteau (Lamiaceae) and Hyptis spicigera Lamarck (Lamiaceae) were first analysed by gas chromatography and by gas chromatography/electron impact mass spectroscopy and then evaluated for toxicity and repellent activity against Sitophilus granarius (L.) (Coleoptera: Dryophthoridae), one of the most serious worldwide stored grain pests. Fifty-six compounds have been identified in the essential oil of H. suaveolens: monoterpene hydrocarbons were the most represented volatiles (64.1%), followed by sesquiterpene hydrocarbons (24.0%), oxygenated monoterpenes (8.1%) and oxygenated sesquiterpenes (2.4%). Diterpenes and non-terpene derivatives were scarcely represented. Sixty compounds have been identified in the essential oil of H. spicigera: monoterpene hydrocarbons were the most represented class of volatiles (70.4%), followed by sesquiterpene hydrocarbons (22.6%). Results from topical applications on insects showed that both essential oils had an effective insecticidal activity. The complete kill of S. granarius was observed 24 h after treatment at a minimum effective dose of 0.4 and 0.6 ll per insect with H. suaveolens and H. spicigera oil, respectively. Results from repellency tests showed that the two essential oils had a repellent activity on S. granarius adults: at the lowest dose (2 9 10 -4 ll oil per cm 2 ), H. spicigera essential oil exhibited a higher repellent effect in comparison to H. suaveolens. No significant differences were observed for the repellent effect between the two essential oils at the highest dose (2 9 10 -2 ll oil per cm 2 ).

A multiresidue method for analysis of 90 pesticides with different physico-chemical properties in fruits and vegetables was developed. The method involves a rapid and small-scale extraction procedure with acetone using vortex mixing. Solid-phase extraction (SPE) on a highly cross-linked polystyrene divinylbenzene column (LiChrolut EN) was used for clean-up and pre-concentration of the pesticides from the water-diluted acetone extracts. For most fruit and vegetable samples this partial clean-up was sufficient, but some of them with more co-extracting substances need further clean-up (cereals, spinach, carrots, etc.). Diethylaminopropyl (DEA) modified silica was used for efficient removal of interferences caused by various organic acids, sugars, etc. The pesticide residues were determined by gas chromatography with a mass selective detector (GC-MS). The majority of pesticide recoveries for various fruits and vegetables were >80% in the concentration range from 0.01 to 0.50 mg/kg, except for the most polar pesticides (methamidophos, acephate, omethoate) which cannot be determined by this method. The limit of quantitation for most of the pesticides was 0.01 mg/kg with majority of relative standard deviations (R.S.D.s) below 10%.

To obtain accurate information for absorbed dose calculations in water for kilovoltage x-rays, the photon spectrum, planar fluence and the angular distribution of the photons at the collimator exit of the x-ray unit have to be known. The only way to obtain this information is by Monte Carlo (MC) simulation. Compared with the situation for high-energy photons and electrons, where in recent years numerous papers have been devoted to MC modelling of complete clinical accelerator units, there is a lack of similar work for kV x-ray units. A reliable MC model for a kV x-ray unit would allow the output information to be used in a treatment planning system for regular and irregular treatment fields. Furthermore, with MC simulation, perturbation factors of dose-measuring devices, such as those specified in codes of practice, can be calculated.

Non-thermal plasma jets in open air are composed of ionization waves commonly known as 'plasma bullets' propagating at high velocities. We present in this paper an experimental study of plasma bullets produced in a dielectric barrier discharge linear-field reactor fed with helium and driven by microsecond high-voltage pulses. Two discharges were produced between electrodes for every pulse (at the rising and falling edge), but only one bullet was generated. Fast intensified charge coupled device camera imaging showed that bullet velocity and diameter increase with applied voltage. Spatially resolved optical emission spectroscopy measurements provided evidence of the hollow structure of the jet and its contraction. It was shown that the pulse amplitude significantly enhances electron energy and production of active species. The plasma bullet appeared to behave like a surface discharge in the tube, and like a positive streamer in air. A kinetics mechanism based on electron impact, Penning effect and charge transfer reactions is proposed to explain the propagation of the ionization front and temporal behavior of the radiative species.

A new method is described for the simultaneous analysis of nitro and polycyclic musks in air samples. Additional considerations are given to the aspects of sample preparation and blank problems. For the first time concentration levels of synthetic musks in selected Norwegian air samples were determined. In a preliminary investigation using ambient air samples prepared for the determination of persistent organic pollutants, musk xylene concentrations were between 8 and 19 3 pg / m . A new sample preparation for the simultaneous analysis of polycyclic and nitro musks is presented. Both GC-electron impact (EI) MS and GC-negative ion chemical ionisation (NICI) MS were compared as detection methods. GC-EI-MS is to be preferred for the determination of synthetic musks since GC-NICI-MS is not sensitive enough for the determination for polycyclic musks. Blank problems occurred which have to be carefully considered during the whole work-up procedure. One indoor air sample was taken in the laboratory where the clean-up of the samples took place to evaluate laboratory air contamination. A concentration for 1, 3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethyl-cyclo[g]-2-ben-3 zopyrane of 2470 pg / m was found using gas chromatographic separation coupled with mass spectrometric detection in the electron impact mode (GC-low-resolution EI-MS). A set of four ambient air samples taken nearby the institute facilities was 3 analysed for both nitro and polycyclic musks. For polycyclic musks, concentrations up to 130 pg / m (GC-EI-MS) were 3 determined and for musk xylene a concentration maximum in ambient air samples 54 pg / m (low resolution EI-MS) was found. Critical considerations about laboratory contamination, clean-up and analysis of ambient air samples are given.

A rapid, specific and sensitive multiresidue method based on the modified Quick Easy Cheap Effective Rugged and Safe (QuEChERS) sample preparation method and gas chromatography with the electron impact mass spectrometric detection in the selected ion monitoring mode (GC-MS-SIM) using one target and two qualifier ions for the routine analysis of 107 pesticides in cabbage and radish has been developed. The recoveries for all the pesticides studied were from 80% to 115% with relative standard deviation lower than 15% in the concentration range of 0.030-0.360 mg/kg. The limit of quantitation (LOQ) for most compounds met MRLs for pesticides in cabbage and radish in Korea. This method was successfully applied to analysis commercial cabbage and radish samples.

The volatile constituents of the star apple (Chrysophyllum cainito L.) growing in Cuba were analysed by GC-MS. One hundred and four compounds were identified in the aroma concentrate, of which (E)-2-hexenal, 1-hexanol, limonene, linalool,˛-copaene and hexadecanoic acid were found to be the major constituents. The presence of many terpenic compounds is thought to contribute to the unique flavour of the star apple fruit.

Electronic state spectroscopy of CH3COOH has been investigated using Vacuum UltraViolet (VUV) photo-absorption spectroscopy in the energy range 3.5–10.6eV. The availability of a high-resolution photon beam (∼0.075nm) has allowed detailed analysis of the vibrational progressions and allowed us to propose, for the first time, new assignments for several Rydberg series. Excited states located in the 10–14eV region have been studied

This paper focuses on the rudimentary principles of discharge physics. The kinetic theory of electron transport in gases relevant to planetary atmospheres is examined and results of detailed Boltzmann kinetic calculations are presented for a range of applied electric fields. Comparisons against experimental swarm data are made. Both conventional breakdown and runaway breakdown are covered in detail. The phenomena of transient luminous events (TLEs), particularly sprites, and terrestrial gamma-ray flashes (TGFs) are discussed briefly as examples of discharges that occur in the terrestrial environment. The observations of terrestrial lightning that exist across the electromagnetic spectrum and presented throughout this volume fit well with the broader understanding of discharge physics that we present in this paper. We hope that this material provides the foundation on which explorations in search of discharge processes on other planets can be based and previous evidence confirmed or refuted. R. Roussel-Dupré ( ) · J.J. Colman · E. Symbalisty

The mass spectra of benzo-15-crown-5 and benzo-l 8-crown-6 were investigated by mass spectrometry with different inlet systems, such as direct introduction, gas chromatography and liquid chromatography inlets. Different ionisation methods such as electron impact, chemical ionisation, electron capture or negative ion chemical ionisation were also studied. The results and the specific problems encountered for this group of substances are discussed based on the spectra obtained.

We examine the effect of cluster size on the interaction of Ar55-Ar2057 with intense extreme ultraviolet (XUV) pulses, using a model we developed earlier that includes ionization via collisional excitation as an intermediate step. We find that the dynamics of these irradiated clusters is dominated by collisions. Larger clusters are more highly collisional, produce higher charge states, and do so more rapidly than smaller clusters. Higher charge states produced via collisions are found to reduce the overall photon absorption, since charge states of Ar 2+ and higher are no longer photo-accessible. We call this mechanism collisionally reduced photoabsorption, and it decreases the effective cluster photoabsorption cross-section by more than 30% for Ar55 and 45% Ar2057. An investigation of the shell structure soon after the laser interaction shows an almost uniformly charged core with a modestly charged outer shell which evolves to a highly charged outer shell through collisions. This leads to the explosion of the outer positive shell and a slow expansion of the core, as was observed in mixed clusters at shorter wavelength . The time evolution of the electron kinetic energy distribution begins as a (mostly) Maxwellian distribution. Larger clusters initially have higher temperature, but are overtaken by smaller temperature after the laser pulse. The electron velocity distribution of large clusters quickly become isotropic while smaller clusters retain the inherent anisotropy created by photoionization. Lastly, the total electron kinetic energy distribution is integrated over the spacial profile of the laser and the log-normal distribution of cluster size for comparison with a recent experiment , and good agreement is found.

Optical emission spectroscopy is used to characterize the production of active species as a function of hydrogen concentration in the mixture under different operating conditions. A major concern is to enhance the concentration of the active species by hydrogen addition that carry several electron volts energy above their ground states, and thus affect the surface chemistry. The emission intensity of the selected optical transitions of molecular and atomic species is measured to determine the functional dependence of their radiative states. The relative ground state molecular ion density [N + 2 ] is measured from the emission intensity of the first negative band head (λ = 391.4 nm, 0-0) by considering the fact that in low temperature plasma, ion with single charge is produced by the electron impact, and the ion density is proportional to the electron density. It is found that the concentration of the active species may be enhanced significantly by selecting an appropriate gas composition and operating parameters. The SS-304 samples are nitrided under the optimum conditions for 4, 8, 12 and 16 hours and hardness values are found to increase five times for 16 hours treatment time. The optimized discharge conditions are found favorable for plasma ion nitriding.

The mass spectra of unlabelled and specifically labelled triterpenes and derivatives were recorded using thermospray liquid chromatography (TSP-LC) and electron impact (EI) ionization. These mass spectra were used for the development of assays to characterize the products from the in vitro oxidative biodegradation of triterpenoids and the identification of compounds in plant extracts. Analysis using gas chromatography-mass spectrometry (GC-MS) with EI ionization of the free products, acetates and trimethylsilyl derivatives, showed lower limits of detection and higher selectivity compared with those with TSP-LC ionization. TSP-LC ionization may be useful for the determination of the molecular ions of highly oxygenated tritepenoids. Accurate masses of the EI fragment ions were recorded for triterpenes of the lupane series and fragmentation routes are discussed. Based on these characteristic fragmentations, 0-methyl-P-lupeol has been identified in plant extracts from Orbygnia species.

Plasmas produced in a cold-cathode Penning discharge have been studied for possible use as an active ionizing medium in commercial quadrupole mass/energy analyzers for detection of low-energy neutral beams. Two distinct Penning discharge modes have been examined: ͑1͒ high-pressure ͑HP͒ mode and ͑2͒ high magnetic field ͑HMF͒ mode. It is shown that the ionization efficiency in the HP mode is independent of the length of ionization region; however, somewhat high working pressures ͑p Ͼ 10 −4 Torr͒ and large discharge currents limit the practical use of this mode. This is not the case in the HMF mode, which appears at lower pressures, with an effective ionization region length of the order of electron cyclotron radius. The design and operation of a compact ͑5 ϫ 4 ϫ 4 cm 3 ͒, low-maintenance ionizer based on a Penning cell with permanent magnets is described. The ability to ionize 40 eV neutral-argon beams with subsequent detection in a Hiden EQP energy-resolved mass spectrometer is shown. The ionization efficiency of the ionizer was found to be as high as 10 −3 . Unlike conventional electron impact ionizers, the Penning discharge configuration allows to eliminate the thermal background component in the detected signal. The ionizer has potential application for the detection of hyperthermal neutral beams of various species.

Immersion stir bar sorptive extraction-gas chromatography-mass spectrometry was used to analyse the volatile organic components of English vineyard grape juices. Four juices, Huxelrebe, Ortega, Schönburger and Siegerrebe, of the 2004 season, were from a commercial vineyard. The fifth, Madeleine Angevine 7672, of the 2000 vintage, was from a private vineyard. Madeleine Angevine juice exhibited the greatest number (113) of identified volatile components, followed by Siegerrebe, Huxelrebe, Schönburger and Ortega, with 78, 74, 70 and 69, respectively. Many compounds are common to all five varieties and very few of the more concentrated components are unique to a particular variety, except (E)-anethole, estragole and methyl salicylate, which were unique to Madeleine Angevine, for these particular vintages. Of the compounds that are common to more than two varieties, Madeleine Angevine had the highest levels of (E)-ethyl cinnamate, hexanol, (E)-2-hexenol, hotrienol, limonene and (E)-methyl cinnamate. Siegerrebe had the highest concentrations of β β β β β -citronellol, diendiol-I, geraniol, dihydromethyl jasmonate, linalool (32 000 ng/l), (Z)-and (E)-linalool oxide (both furanoid and pyranoid forms) and α α α α α-terpineol. This variety also had high levels of 1-hexanol, (E)-2-hexenal and (E)-2-hexenol. Huxelrebe had the highest concentrations of (E)-2-hexenal and (E)-theaspirane; Schönburger had the highest levels of (Z)-3-hexenol, nerol and nerol oxide; and Ortega had the highest concentrations of β β β β β -damascone and β β β β β -damascenone.

2,5-Dioxypiperazine (DOPZ) was covalenty bonded as a chelating compound to chloropropyltrimethoxysilane (Si-Cl) for the formation of a new chemisorbed silica [Si-(CH 2 ) 3 -DOPZ]. Physisorbed silica-loaded-2,5-dioxypiperazine [Si-DOPZ] was also synthesized via a physical adsorption approach. Elucidation of the chemisorption and physisorption of 2,5-dioxypiperazine onto silica was confirmed on the basis of 70 eV electron impact mass spectrometric (70 eV EI-MS) mode of ionization via a direct insertion probe (DIP) as a promising technique for providing characteristic fragment ion peaks. The metal probe testing method and elemental analysis were applied to determine the surface coverage values and these were found to be 0.179 and 0.160 mmol g À1 for [Si-(CH 2 ) 3 -DOPZ] and 0.251 mmol g À1 for [Si-DOPZ]. [Si-(CH 2 ) 3 -DOPZ] was characterized by high stability in acidic and buffer solutions, pH 1-7, compared to [Si-DOPZ]. Differential scanning calorimetry studies (DSC) for the modified silica were performed to evaluate the various thermodynamic and kinetic parameters of the thermal degradation processes, and these have been enumerated. The results obtained by both EI-MS and DSC are very similar in many respects. Metal chelation and stoichiometric properties of chemically modified silica were evaluated on the basis of the metal binding capacity, distribution coefficient and separation factor for a series of metal ions. The evaluated results refer to the high metal chelating properties of [Si-(CH 2 ) 3 -DOPZ] for cadmium(II), lead(II) copper(II) and mercury(II). These four [Si-(CH 2 ) 3 -DOPZ]metal complexes were also synthesized and the identified stoichiometric ratios were found to be 1:2 based on the nitrogen and metal analysis. EI-MS via 70-eV ionization was also used as a potential method for further confirmation of the metal complex formation based on structure and fragmentation elucidation. DSC studies of these four metal complexes were also performed and evaluated.

The carbon dioxide reforming of methane to synthesis gas under DC-pulsed plasma was investigated. The effects of specific input energy and feed ratio on the product distribution and also feed conversion was studied. At the input energy of about 11 eV/molecule per methane and/or carbon dioxide the feed conversion of 38% for CH4 and 28% for CO2 and product selectivity of 74% has been attained for H2 and CO at feed flow rate of 90 ml/min. The energy consumption in this work displays potential to further study and optimization of the process. The importance of the electron impact reactions in the process was discussed. The results show that by prudent tuning of system variables, the process be able to run in the way of synthesis gas, instead of hydrocarbon production.

The steady radial distribution of chemical species in a wire-to-cylinder ozone generator filled with pure oxygen has been computed by applying four different plasma chemistry models of increasing complexity. The most complete model considers ten species (e, 02+, 02-, 0 3 -, 0-, 02, o~('A.J, o~( ' z~) , 0 and 03) and 79 reactions, including ionization by electron impact, electron attachment and detachment, electron-ion recombination, charge transfer, etc. The chemical model is coupled with the electrical model through Poisson's equation. The spatially averaged ozone density has been computed as a function of the current intensity and compared with the experimental values obtained by W spectroscopy.

We have studied the structure of 4 He droplets doped with magnesium atoms using density functional theory. We have found that the solvation properties of this system strongly depend on the size of the 4 He droplet. For small drops, Mg resides in a deep surface state, whereas for large-size drops it is fully solvated but radially delocalized in their interior. We have studied the 3s3p 1 P 1 ← 3s 21 S 0 transition of the dopant, and have compared our results with experimental data from laser-induced fluorescence ͑LIF͒. Line-broadening effects due to the coupling of dynamical deformations of the surrounding helium with the dipole excitation of the impurity are explicitly taken into account. We show that the Mg radial delocalization inside large droplets may help reconcile the apparently contradictory solvation properties of magnesium as provided by LIF and electronimpact ionization experiments. The structure of 4 He drops doped with two magnesium atoms is also studied and used to interpret the results of resonant two-photon-ionization ͑R2PI͒ and LIF experiments. We have found that the two solvated Mg atoms do not easily merge into a dimer, but rather form a weakly bound state due to the presence of an energy barrier caused by the helium environment that keeps them some 9.5 Å apart, preventing the formation of the Mg 2 cluster. From this observation, we suggest that Mg atoms in 4 He drops may form, under suitable conditions, a soft "foamlike" aggregate rather than coalesce into a compact metallic cluster. Our findings are in qualitative agreement with recent R2PI experimental evidence. We predict that, contrarily, Mg atoms adsorbed in 3 He droplets do not form such metastable aggregates.

This article reviews recent literature on current methodologies based on chromatography coupled to mass spectrometry to analyze phenolic compounds with endocrine-disrupting capabilities. For this review we chose alkylphenol ethoxylates, bisphenol A, bisphenol F, and their degradation products and halogenated derivatives, which are considered important environmental contaminants. Additionally, some related compounds such as bisphenol diglycidylethers were included. Growing attention has been paid to the mass spectrometric characterization of these compounds and the instrumentation and strategies used for their quantification and confirmation. The current use of gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) methodologies with different mass spectrometers and ionization and monitoring modes is discussed. Practical aspects with regards to the use of these analytical techniques, such as derivatizing reagents in GC-MS, ion suppression in LC-MS, and the most problematic aspects of quantification, are included in the discussion.

Transmission electron energy-loss spectrometry was used to investigate the electronic states of metallic Li and LiC 6 , which is the Li-intercalated graphite used in Li-ion batteries. The Li K edges of metallic Li and LiC 6 were nearly identical, and the C K edges were only weakly affected by the presence of Li. These results suggest only a small charge transfer from Li to C in LiC 6 , contrary to prior results from surface spectra obtained by x-ray photoelectron spectroscopy. Effects of radiation damage and sample oxidation in the transmission electron microscopy are also reported.