Electron capture thermal

The PDM-ECD kinetic method demonstrated above is expected to be applicable to any IM reaction where (1) the reactant ion can be generated by a thermal electron capture reaction, (2) the neutral reactant does not react significantly with thermal electrons, and (3) either the reactant or the product negative ion possess a uniquely high PD cross section in some region of the UVA is/near-IR spectral range between 250 and 1200 nm. ... 

C,HJ (Benzene) sf6- >0 Unspecified Photoionization -mass spectrometry Single-source electron-impact ionization-mass spectrometry CeH (QHj —)C,2H SF6 (XFVSFJXFj- X-Se.Te,U SF6-(TeF6 SF6,F)TeF5- The ion SF - produced by thermal electron capture of SF in a vibrational degree of excitation equal to electron affinity of the neutral 116a... 

Electron thermalization Thermal electron capture Reaction of rare gas excited states Cation dimerization Two body ion-ion recombination Three body ion-ion recombination Exciplex fluorescence... 

By addition of a dissociative thermal electron capturing gas such as CH2Brj, which quantitatively produces the atomic Br anion, the three body recombination process for an anion can be determined in isolation of any two-body mutual neutralization reactions. For irradiated xenon-CH2Br2 gas mixtures, the total emission at 282 nm was foxmd to consist of X-rays, xenon dimer fluorescence, and XeBr (B,C) exciplex fluorescence formed from both ionic recombination and xenon excited-state reaction [67]... 

The Kinetics oe Thermal Electron Capture and Thermal Electron Detachment... 

In order to later estimate thermal electron capture rate constants, Van Doren et have calculated the polarizabilities of the SF C1... 

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

The special problems for vaUdation presented by chiral separations can be even more burdensome for gc because most methods of detection (eg, flame ionization detection or electron capture detection) in gc destroy the sample. Even when nondestmctive detection (eg, thermal conductivity) is used, individual peak collection is generally more difficult than in Ic or tic. Thus, off-line chiroptical analysis is not usually an option. Eortunately, gc can be readily coupled to a mass spectrometer and is routinely used to vaUdate a chiral separation. 

The detector. The function of the detector, which is situated at the exit of the separation column, is to sense and measure the small amounts of the separated components present in the carrier gas stream leaving the column. The output from the detector is fed to a recorder which produces a pen-trace called a chromatogram (Fig. 9.1fr). The choice of detector will depend on factors such as the concentration level to be measured and the nature of the separated components. The detectors most widely used in gas chromatography are the thermal conductivity, flame-ionisation and electron-capture detectors, and a brief description of these will be given. For more detailed descriptions of these and other detectors more specialised texts should be consulted.67 69... 

Negative Ion Chemical Ionization Negative ions are produced under ci conditions by electron capture. Under the higher pressure conditions of the ci ion source, electrons, both primary (those produced by the filament) and secondary (produced during an ionization event), undergo collisions until they reach near-thermal energies. Under these conditions, molecules... 

This technique detects substances qualitatively and quantitatively. The chromatogram retention time is compound-specific, and peak-height indicates the concentration of pollutant in the air. Detection systems include flame ionization, thermal conductivity and electron capture. Traditionally gas chromatography is a laboratory analysis but portable versions are now available for field work. Table 9.4 lists conditions for one such portable device. 

The product gases were continuously analyzed for NO and NO2 using a chemiluminescent analyzer, and discontinuously for N2O, N2, CO, CO2 and O2 by GC equipped with a thermal conductivity detector and an electron capture detector, specifically for the N2O analysis, using a Poraplot Q column and a molsieve 5A column for separation. 

Flow limitations restrict application of the DFI interface for pSFC-MS coupling. pSFC-DFI-MS with electron-capture negative ionisation (ECNI) has been reported [421], The flow-rate of eluent associated with pSFC (either analytical scale - 4.6 mm i.d. - or microbore scale 1-2 mm, i.d.) renders this technique more compatible with other LC-MS interfaces, notably TSP and PB. There are few reports on workable pSFC-TSP-MS couplings that have solved real analytical problems. Two interfaces have been used for pSFC-EI-MS the moving-belt (MB) [422] and particle-beam (PB) interfaces [408]. pSFC-MB-MS suffers from mechanical complexity of the interface decomposition of thermally labile analytes problems with quantitative transfer of nonvolatile analytes and poor sensitivity (low ng range). The PB interface is mechanically simpler but requires complex optimisation and poor mass transfer to the ion source results in a limited sensitivity. Table 7.39 lists the main characteristics of pSFC-PB-MS. Jedrzejewski... 

VDU screen via suitable electronic amplifying circuitry where the data are presented in the form of an elution profile. Although there are a dozen or more types of detector available for gas chromatography, only those based on thermal conductivity, flame ionization, electron-capture and perhaps flame emission and electrolytic conductivity are widely used. The interfacing of gas chromatographs with infrared and mass spectrometers, so-called hyphenated techniques, is described on p. 114 etseq. Some detector characteristics are summarized in Table 4.11. 

Detectors range from the universal, but less sensitive, to the very sensitive but limited to a particular class of compounds. The thermal conductivity detector (TCD) is the least sensitive but responds to all classes of compounds. Another common detector is the flame ionization detector (FID), which is very sensitive but can only detect organic compounds. Another common and very sensitive detector is called electron capture. This detector is particularly sensitive to halogenated compounds, which can be particularly important when analyzing pollutants such as dichlorodiphenyltrichloroethane (DDT) and polychlorobiphenyl (PCB) compounds. Chapter 13 provides more specific information about chromatographic methods applied to soil analysis. 

There are four main types of detectors used in GC thermal conductivity detector (TCD), also called a hot wire detector, flame ionization detector (FID), electron capture detector (ECD), and quadruple mass spectrometer (MS)... 

Gas Thermal conductivity (TC or TCD) Flame ionization (FID) Electron capture (ECD) Mass spectrometry (MS or GC-MS)... 

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