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Detection — Analytical
Published in Lorris G. Cockerham, Barbara S. Shane, Basic Environmental Toxicology, 2019
Christine A. Purser, Arthur S. Hume
Another very sensitive and selective ionization type of detector is the electron capture detector (ECD), used for compounds containing electronegative substances such as halogens (McNair and Bonelli, 1969; Marsden, 1989). This detector is unique in that it measures the loss of electrical current rather than its production. The detector uses radioactive isotopes, the most common being 63Ni. During the decay process, this isotope releases beta particles which collide with incoming carrier gas molecules, producing many secondary, low energy electrons. With the placement of electrodes in the detector cavity, these electrons can be captured. They produce a “standing current” (background current) measured by an electrometer. With the introduction of a sample containing electron absorbing molecules, the secondary electrons are captured by these molecules, producing negatively charged ions. The absorption of the secondary electrons by electron absorbing molecules reduces the amount of electrons which can be captured; therefore, the standing current is reduced and produces a negative peak. This peak is inverted during amplification by the electrometer to give a positive response on the integrator or the computer. The ECD, more sensitive than the FID to the compounds discussed above, has found application in the measurement of chlorinated pesticides, polychlorinated biphenyls, TCDD (dioxin isomers), halogenated VOCs, and phthalates (Supelco, Inc., 1986; Rhoades et al., 1988; Donnelly and Sovocool, 1989; Kirshen and Almasi, 1989; Marsden, 1989).
Chromatographs—Gas
Published in Béla G. Lipták, Analytical Instrumentation, 2018
Electron Capture Detector In the electron capture detector (ECD), the column effluent passes between two electrodes of the PID, one of which has been treated with a radioactive source (tritium or nickel-63, with the latter being preferred because of extended detector stability) that emits high-energy electrons. These electrons produce large quantities of low-energy thermal electrons in the carrier gas, which are in turn collected by the other electrode to produce a steady-state current in the presence of pure carrier gas. Compounds eluting from the column that have an affinity for thermal electrons reduce this steady-state current thereby producing the chromatogram. The detector is thus highly selective, with halogenated compounds being the most responsive (detection at the picogram level). Other groups exhibiting good selectivity include anhydrides, peroxides, conjugated car-bonyls, nitriles and nitrates, and sulfur-containing compounds (Figure 11aa).
Introduction
Published in Jamie Bartram, Richard Ballance, Water Quality Monitoring, 1996
Jamie Bartram, Richard Ballance
The electron capture detector (ECD) is operated by passing the effluent from the gas chromatographic column over a radioactive beta-particle emitter, usually nickel-63 or tritium, adsorbed on platinum or titanium foil. An electron from the emitter ionises the carrier gas and produces a burst of electrons. About 100 secondary electrons are produced for each initial betaparticle. After further collisions the energy of these electrons is reduced to the thermal level and they can be captured by electrophilic sample molecules. The electron population is collected by applying a voltage pulse to the cell electrodes, and the pulse interval is automatically adjusted to maintain a constant current. The change in the pulse rate when a sample enters the detector is related to the concentration of contaminant in the sample. The detector is highly sensitive to molecules containing halogens, peroxides, quinones and nitro groups but is insensitive to functional groups such as amines, alcohols and hydrocarbons.
Evaluation of the effectiveness of bioaugmentation and biostimulation in atrazine removal in a polluted matrix using degradation kinetics
Published in Soil and Sediment Contamination: An International Journal, 2023
Godwin O. Aliyu, Chukwudi U. Anyanwu, Chukwudi I. Nnamchi, Chukwudi O. Onwosi
Briefly, dry soil samples (20 g) were collected for pesticide extraction in screw cap bottles. About 100 ml acetone-hexane (1:1) was added to the sample, and the cap screwed tightly. This mixture was agitated at 120 rpm for 24 h, filtered using filter paper and the filtrate evaporated at 40°C using a rotary vacuum evaporator. The evaporated filtrate was passed through a mixture of activated florisil (magnesium silicate) and anhydrous Na2SO4 (2:1 w/w) in a column for purification, using n-hexane as eluent, before transferring into a clean evaporating flask and evaporated to dryness. The dry eluate was dissolved in 1 ml acetone for chromatographic analysis. Gas chromatography coupled with an electron capture detector (Buck M910 Scientific GC, USA), as described by Camel (1997), was used to quantify the residual atrazine in soil samples. Tests were performed in triplicates by drawing three soil samples from each treatment mesocosm. A HP5-MS capillary column (model Agilent 1909IS 433E) with a 0.25 mm i.d., 30 m, and 0.25 µm phase film diameter was used. The carrier gas was helium at a flow of 1 mL/min. The temperature programme was an isothermal period of 5 min at 50°C, then, increased to 150°C at a rate of 20°C/min and thereafter to a final holding temperature of 250°C at the rate of 10°C/min. The final isothermal period was 5 min.
Remediation of endosulfan-contaminated water by hairy roots: removal and phytometabolization assessment
Published in International Journal of Phytoremediation, 2023
Patricia A. Lucero, Cynthia Magallanes-Noguera, Fernando A. Giannini, Mirtha Nassetta, Alejandro A. Orden, Marcela Kurina-Sanz
Detection and quantification of endosulfan isomers and their metabolites were performed by gas chromatography with electron capture detector (GC‐ECD‐Ni63) following Method A as described below. Alternatively, Methods B and C were used to confirm the identity of endosulfan metabolites. Peaks were identified by comparing their retention times with standards. Quantification of endosulfan isomers and their metabolites was performed with a calibration curve prepared by injection of known concentrations of standards in isooctane. Method A: Perkin Elmer Autosystem XL chromatograph; column: Restek® 1 ms; oven program: (50/3/20/210/0/5/260/10); injector T: 240 °C; carrier gas: N2; carrier gas flow: press: 49 psi – Aux1: 29 psi; split flow: 40 mL min−1; injection volume: 1 μL; detector T: 400 °C. Method B: Varian CP3800 chromatograph; column: Restek® 5; oven program: (50/3/20/210/0/5/260/9); injector T: 240 °C; N2 was used as carrier gas at a flow rate of 2 mL min−1; split flow: 5 mL min−1; injection volume: 1 μL; detector T: 300 °C. Method C: Varian CP3800 Chromatograph; column: SPB608; oven program: (150/4/8/250/30/0/0/0); injector T: 240 °C; N2 was used as carrier gas at a flow‐rate of 2 mL min−1; split flow: 5 mL min−1; injection volume: 1 μL; detector T: 300 °C.
Chlorination of L-tyrosine and metal complex: degradation kinetics and disinfection by-products generation
Published in Environmental Technology, 2022
Tuqiao Zhang, Rongrong Jiang, Lei Fang, Xiaowei Liu, Lijie Jiang
Two types of DBPs (TCM, Haloacetic acids) were measured during L-Tyr chlorination. Two samples were pre-treated by liquid–liquid extraction with MTBE for TCM detection. Two samples were pre-treated by liquid–liquid extraction with MTBE and derivatized with sulfuric acid methanol for Haloacetic acids detection. The concentrations of TCM and Haloacetic acids were analyzed by using a gas chromatography-electron capture detector (GC/ECD) (Agilent Technologies, USA). The column used was an HP-5 capillary column (30 m × 0.32 mm × 0.25 μm) (Agilent Technologies, USA) with a flow rate of 2 mL/min. The split injection mode was used. For TCM, the temperature of the injector and the detector were 210°C and 290°C, respectively and the temperature programme was 35°C for 13 min; increased to 200°C at 30°C/min, and maintained for 3 min. For HAAs, the temperature of the injector and the detector were 175°C and 300°C, respectively and the temperature programme was 35°C for 5 min; increased to 90°C at 5°C/min, and maintained for 5 min.