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Chemical Analysis in Environmental and Toxicological Chemistry
Published in Stanley E. Manahan, Environmental Chemistry, 2022
The component that primarily determines the sensitivity of gas chromatographic analysis and, for some classes of compounds, the selectivity as well is the detector. One such device is the thermal conductivity detector, which responds to changes in the thermal conductivity of gases passing over it. The electron-capture detector, which is especially useful for halogenated hydrocarbons and phosphorus compounds, operates through the capture of electrons emitted by a beta-particle source. The flame-ionization gas chromatographic detector is very sensitive for the detection of organic compounds. It is based on the phenomenon by which organic compounds form highly conducting fragments, such as C+, in a flame. Application of a potential gradient across the flame results in a small current that can be readily measured. The mass spectrometer, described in Section 24.10, can be used as a detector for a gas chromatograph. The combined gas chromatograph/mass spectrometer (GC/MS) and combined high-performance liquid chromatograph/mass spectrometer (HPLC/MS) instruments are especially powerful analytical tools for organic compounds.
Radioactivity and Nuclear Chemistry
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
Other types of decay include positron decay, as well as electron capture. Positron decay releases a short-lived positron particle, which is a particle like an electron, but with a positive charge. Electron capture is the capture of an electron that is in an orbital in the atom by a proton. The proton and the electron combine to form a neutron. Both of these types of decays are accompanied by the release of a high-energy photon (X-ray or gamma ray).
Fundamental Concepts and Quantities
Published in Shaheen A. Dewji, Nolan E. Hertel, Advanced Radiation Protection Dosimetry, 2019
The term beta decay is used to describe three processes—electron emission, positron (anti-electron) emission, or electron capture. The latter two processes will be discussed in later sections. Beta decay involves the transition of a neutron into a proton-electron pair, and results in an increase by one of the Z number: XZAN→XZ+1AN−1+e−
Simulated performance evaluation of d-Be compact fast neutron source
Published in Journal of Nuclear Science and Technology, 2023
As the final part of the simulation results, the production of radioactive nuclides is discussed. In the p+Li neutron source, the 7Li(p,n)7Be reaction produces the same amount of 7Be (T1/2 = 53.2 days) as neutrons. 7Be decays to 7Li by electron capture and 10.4% of it emits 478 keV gamma-ray. On the other hand, the d+Be neutron source produces tritium (T1/2 = 12.32 years) via the 9Be(d,t) reaction. According to the evaluated values of JENDL-5, the 9Be(d,t) reaction cross section in the energy range from 1.5 to 2.5 MeV is about half that of 9Be(d,n) reaction. From the simulation results, we estimate the radioactivity produced in one month under the condition that the neutron sources are operated for eight hours per day, five days per week. The results are summarized in Table 1. As presented in the table, the produced radioactivity is higher in the p+Li neutron source due to the shorter half-life of 7Be. In the operation of these neutron sources, it is necessary to pay attention to the handling of the activated target.
Preparation and photocatalytic properties of DBD plasma F/N co-doping modified TiO2
Published in Phase Transitions, 2023
Xiong Li, Lianhong Zhang, Hongbo Wu, Qiang Li, Cheng Hu
Photoluminescence is an important tool for studying semiconductor electron–hole pairs, characterizing oxygen vacancies and surface defects [43]. The valence band leaves holes, and in the absence of electron capture agents, electron–hole recombination will quickly recombine. Generally speaking, the stronger the fluorescence, the more intense the electron recombination, and the weaker the fluorescence, the more intense the inhibition of electron–hole recombination [44,45]. The photoluminescence spectra of TiO2, ND-80, and NHD-80 are shown in Figure 6. The fluorescence intensity of ND-80 and NHD-80 is weaker than that of pure TiO2, indicating that the photogenerated electrons of ND-80 and NHD-80 catalysts are recombined. The strong inhibition is attributed to the combined effect of N/F doping and surface ≡Ti-F bonds, while TiO2 contains a large number of bulk defects, which instead become new centers for electron–hole recombination (Figure 10).
Occurrence of agricultural pesticides in Mississippi Delta Bayou sediments and their effects on the amphipod: Hyalella azteca
Published in Chemistry and Ecology, 2021
R. E. Lizotte, R. W. Steinriede, M. A. Locke
Approximately 10 g of dry homogenised ground bayou sediment was subsampled or 0.125 g H. azteca tissue was sampled for pesticide analysis using an Agilent Model 7890A gas chromatograph equipped with Agilent 7693 autosampler and dual G4513A autoinjectors, dual split-splitless inlets, dual capillary columns, Agilent ChemStation, and autoinjector set at 1.0 µL injection volume fast mode (Agilent Technologies, Inc., Wilmington, Delaware USA). The system was used for 14 targeted pesticide analyses according to Smith and Cooper [13] and Smith et al. [14] (Table 2). The Agilent 7890A GC was equipped with two micro electron capture detectors (µECDs). Column oven temperatures were: initial at 65°C for 1 min; ramp at 10°C to 175°C; hold at 175°C for 15 min; ramp at 10°C to 225°C and hold for 34 min. Carrier gas used was ultra-high purity (UHP) helium at 54.5 mL/min and inlet temperature at 250°C. The µECD temperature was 325°C with a constant make-up gas flow of 60 mL/min UHP nitrogen. Sediment sample detection limits in μg/kg were: 5 for clomazone and 2.5 for the remaining 13 pesticides. Animal tissue detection limits in μg/kg were: 400 for clomazone and 200 for the remaining 13 pesticides. Percent recoveries for pesticide standard checks averaged 91.5 ± 6.3% ranging from 82% for clomazone to 108% for p,p’-DDT. Percent recoveries for quality control checks averaged 95.8 ± 7.6% ranging from 79% for Ζ-cypermethrin to 116% for λ-cyhalothrin.