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Air Sampling
Published in Martin B., S.Z., of Industrial Hygiene, 2018
Ionization sensors include a portable gas chromatograph (GC), which is a field instrument capable of separating and identifying many specific gases and vapors in the field. Most portable GCs come with a single detector. There are a number of detectors that can be used in GCs, but the most commonly used detectors are flame ionization detector (FID), photoionization detector (PID), and electron capture detector (ECD). The choice of detector will depend on the chemicals for which monitoring is needed, as well as on the nature of any other contaminants present and the sensitivity required. Both FIDs an PIDs are primarily nonspecific detectors used for the detection of organic compounds. However, the sensitivity of FIDs decreases with increasing substitutions of other elements such as oxygen, sulfur, and chlorine. PIDs can detect organic compounds such as aliphatic, aromatic, and halogenated hydrocarbons, as well as some inorganic compounds such as arsine, phosphine, and hydrogen sulfide, as well as nitric and sulfuric acids. ECD is a very sensitive technique, particularly for halogenated organic compounds, nitrates, conjugated carbonyls, and some organometallic compounds. It is also useful for sulfur hexafluoride and pesticide detection. All three detectors are available as stand-alone instruments.
Chromatography Composition Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Behrooz Pahlavanpour, Mushtaq Ali, C.K. Laird
The ECD is an ionization chamber in which molecules of electronegative species are allowed to attach to or “capture” electrons that have been slowed to thermal velocities by collision with inert gas molecules. The detector consists of a cell containing an emitting radioactive source (usually 63Ni) and purged with inert gas. Electrons emitted from the source are slowed to thermal velocities (thermalized) by collision with the gas molecules and are eventually collected by a suitable electrode, giving rise to a standing current in the cell. If molecules with greater electron affinity are introduced into the cell, some of the electrons are “captured,” forming negative ions that are more massive with less mobile from free electrons, and the current in the cell is reduced. This effect is the basis of the ECD.
Determining DNA Adducts by Electrophore Labeling-GC
Published in Frederick C. Kopfler, Gunther F. Craun, Environmental Epidemiology, 2019
An electrophore is a molecule that captures a low-energy electron in the gas phase. The immediate consequence of this capture is the formation of an anion radical. This event takes place and can be detected in both an electron capture detector (ECD) and in a negative chemical ionization source of a mass spectrometer (MS). In the ECD the loss of the thermal electron is detected, while the MS detects the anion radical or a subsequent anionic fragment derived from this radical.
Understanding to the composition and structure of organic chlorides in petroleum and its distillates
Published in Petroleum Science and Technology, 2019
Some analytical techniques have been used to characterize the molecular structure of organic chlorides in crude oil and its distillates. The most commonly used technique is gas chromatography (GC) equipped with the electron capture detector (ECD). ECD is an ionization detector which has a high selectivity and high sensitivity to the material with electronegativity, such as halogen, sulfur, phosphorus and nitrogen-containing compounds, while no signal response to the electroneutral material, such as alkanes (Concha-Graña et al. 2009).