China
Africa
Explore chapters and articles related to this topic
Sampling and Laboratory Analysis for Solvent Stabilizers
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
Thomas K.G. Mohr, Jeremy Bishop
TCDs were widely used in the early years of GC because of their simplicity, universal applicability, and low cost. Analyte detection is based on changes in the conductivity of the column effluent. The TCD is a destructive detector that can be used in series only after nondestructive detectors. The TCD detects gaseous compounds in the ppm range. TCDs are not generally used for analysis of low-concentration samples as the possibility of false identification of analytes is a large problem. Larger sample volumes are required to achieve increased sensitivity, which in turn requires using a large-diameter chromatographic column (USEPA, 2006b). TCDs are not well suited for detection of 1,4-dioxane and are no longer widely used for environmental sample analysis.
Gas Chromatography
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Yuwen Wang, Mochammad Yuwono, Gunawan Indrayanto
The thermal conductivity detector (TCD) is sometimes referred to as a hot-wire detector or katharometer (also spelled catherometer). It was developed as a very early detector for GC and is based on the changes in the thermal conductivity of the gas stream caused by the presence of analyte molecules. Since TCD responds nonspecifically, it can be used universally for the detection of either organic or inorganic substances. Any component, including nitrogen and oxygen, except the gas used as the carrier gas, can be detected by TCD. The principle of the detection is using a Wheatstone bridge. Two pairs of TCD are used in GC; one pair is placed in the column effluent to detect the analyte, and another is placed before the injector or connected to a separate reference column. There are two basics of TCD design: the “in-line” cell, in which the effluent actually passes directly over the filament, and the “off-line” cell, where the filaments are situated away from the main gases and are only reached by diffusion (Figure 23.18) (Scott, 2001h).
Analytical Chemistry for Industrial Hygienists
Published in Martin B., S.Z., of Industrial Hygiene, 2018
The thermal conductivity detector (TCD) actually predates chromatography, though it is still used because it is such a universal detector. The TCD responds to any compound whose thermal conductivity is different than that of the carrier gas. When helium, which has an exceptionally high thermal conductivity, is used as the carrier gas, most compounds give good sensitivity. When the analyte is present in the carrier gas, the thermal conductivity drops, and less heat is lost to the detector wall. Under constant applied voltage, a filament in the detector will heat up and its resistance will increase. This change is recorded and correlated to the concentration of the compound of interest. The TCD is a nondestructive detector and therefore can be used in series with more selective detectors. As shown in Figure 5.7, two filaments are incorporated in an electrical resistance bridge. It is balanced with pure carrier flowing through dual cells, with a reference filament in one cell. The detector filament’s resistance, and its changes when compounds elute, is registered as a difference relative to the reference filament. In some TCD models, the filaments are replaced by transistors.
Experimental characterization of selected Nigerian lignocellulosic biomasses in bioethanol production
Published in International Journal of Ambient Energy, 2021
A. A. Awoyale, D. Lokhat, A. C. Eloka-Eboka
The crude protein content of the biomass samples was determined using the standard procedure described in AOAC 997.09. The crude protein content in the samples was determined through the determination of the total nitrogen composition using the combustion method. Through the burning process conducted at approximately 900°C, the nitrogen content of the samples was converted to NO3, which is further reduced by copper to form nitrogen gas. The nitrogen gas was then measured by passing the gas via a column that has a thermal conductivity detector (TCD) at the end. The TCD was earlier calibrated by analysing a pure material with a known nitrogen concentration, and ethylenediaminetetraacetic acid which equals 9.59% nitrogen was used for this purpose. Hence, the signal from the TCD can be converted into a nitrogen content. The concentration of nitrogen in the sample was then converted to protein content. A conversion factor of 6.25 (equivalent to 0.16 g nitrogen per gram of protein) was used for the conversion.
Investigation on the effect of superheated water vapor on gas production from pyrolysis of long-flame coal
Published in Chemical Engineering Communications, 2022
Chao Zhang, Yangsheng Zhao, Zijun Feng, Peng Zhao, Xia Wang
The gas phase product components were analyzed using a Shimadzu GC-2014 gas chromatograph. Two detectors, FID and TCD, were used to detect hydrocarbon gases (C1–C5) and other component gases (H2, CH4, CO2, and CO). A standard gas with a composition close to the gas product composition was used to perform a gas concentration calibration before the GC-FID/TCD was used to detect the gas composition. The temperature was maintained at 50 °C for 3 min, increased at a rate of 4 °C/min till 180 °C was reached, and then held for 4 min. High-purity helium was used as the purge gas at a flow rate of 20 mL/min.