Ionisation electron capture detector

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... 

Ionisation detectors. An important characteristic of the common carrier gases is that they behave as perfect insulators at normal temperatures and pressures. The increased conductivity due to the presence of a few charged molecules in the effluent from the column thus provides the high sensitivity which is a feature of the ionisation based detectors. Ionisation detectors in current use include the flame ionisation detector (FID), thermionic ionisation detector (TID), photoionisation detector (PID) and electron capture detector (ECD) each, of course, employing a different method to generate an ion current. The two most widely used ionisation detectors are, however, the FID and ECD and these are described below. 

Electron capture detector. Most ionisation detectors are based on measurement of the increase in current (above that due to the background ionisation of the carrier gas) which occurs when a more readily ionised molecule appears in the gas stream. The electron capture detector differs from other ionisation detectors in that it exploits the recombination phenomenon, being based on electron capture by compounds having an affinity for free electrons the detector thus measures a decrease rather than an increase in current. 

One advantage of gas chromatography is the availability of detectors which respond specifically to certain types of compound. The best known are the electron capture detector for chlorine compounds and the flame photometric detector for nitrogen and phosphorus compounds. If one wants to detect very small molecules such as water or CSj, the standard flame ionisation detector must be replaced by a thermal conductivity detector. 

Electric sector, 295 Electrochromatography, 119 Electrode potential, 348 Electromagnetic separator, 294 Electromigration, 114, 117 Electron capture detector, 36 Electron ionisation, 307 Electro-osmosis, 115 Electro-osmotic flow, 114 Electrophoregram, 113 Electrophoretic mobility, 114 Electrospray, 312 ELISA, 336... 

Llopart-Vizoso et al. [ 114] determined phenols and cresols in soil by direct acetylation followed by gas chromatography headspace analysis. Danis and Albanis [115] also used a technique based on acetylation-gas chromatography. Three gas chromatographic detectors were employed flame ionisation, electron capture and mass spectrometric. 

Karasek et al. [32] determined phenols in soils by extraction with a mixture of benzene and water modified to pH 10 by the addition of 2-methoxyethyl-amine. The phenol in the extract was identified and determined by gas chromatography using a variety of detectors, including flame ionisation, electron capture and mass spectrometry. 

The most common detectors for GC are the non-selective flame ionisation detector and thermal conductivity detector. For element speciation, selectivity is definitely advantageous, allowing less sample preparation and less demanding separation. Of the conventional GC detectors, the electron capture detector is very sensitive for electrophilic compounds and therefore has some selectivity for polar compounds containing halogens and metal ions. It has been used widely... 

Sporek, K. F. New type of argon ionisation, helium electron capture detector for gas chromatography. US-At. Energy Comm. Rpt. Conf-650, 809 (1966). — Anal. Abstr. 14, 3715 (1967). 

Petroleum ether Dieldrin DC-200 on chromosorb WHMDS flame ionisation and electron capture detectors [104]... 

The gas chromatograph is equipped with a 63Ni electron capture detector mounted in parallel with a flame ionisation detector and an auxiliary vent by the use of a column effluent splitter. The separation is performed on a 4.8mm od, 6m long stainless steel column packed with 16.5% silicone oil DC-550 on Chromosorb W AW DMCS. 

Most of the detectors commonly used for gas chromatography have been applied to the detection of the hydrides, among them the thermal conductivity, flame ionisation and the electron capture detector [761],... 

With long and very efficient columns, the time taken for a non-retained compound to reach the end of the column after injection (dead-time) can be several minutes. It is determined by injecting a compound such as methane for a flame ionisation detector or methylene chloride for an electron capture detector. Retention times should really compensate for the dead-time rather than being... 

Electrolytic conductivity detector, 185 Electron capture detector, 184 Electron impact ionisation, 254 Elentol, 707 Elimination of drugs, by the body, 280 by the kidneys, 282 by the liver, 281 Elimination rate constant, 281 Elixicon, 1011... 

A recent method of detection is electron capture negative ionisation (ECNI) as ionization technique in combination with GC-MS analysis. This method is advantageous because it offers a high sensitivity for compounds with four or more bromine atoms [36]. The sensitivity of ECNI for these compounds is approximately 10 times higher than with the use of an electron capture detector (ECD) [5]. In the analytical method which was developed to quantitate PCBs and PBBs in human serum, GC/ECD was used [30]. Because the response, and therefore the sensitivity, of the ECD depends on the position of the halogen on the biphenyl nucleus as well as the number of halogen atoms, it is necessary to run a standard for each compound to be determined [2], The use of narrow bore (0.15 mmi.d.) capillary columns is advised to obtain the required resolution [5]. 

EB ECD EDTA EI+ EPA EPTC ESR EU Eckman-Birge-grab sampler Electron capture detector Ethylenediaminetetraacetic acid Postive electron impact ionisation Environmental protection agency (USA) S-Ethyldipropylcarbamate Electron spin resonance (spectroscopy) European union... 

The Shimadzu GC-15A and GC-16A systems are designed not only as independent high-performance gas chromatographs but also as core instruments (see previously) for multi-GC systems or computerised laboratory automation systems. Other details of these instruments are given in Table 5.1. The Shimadzu GC-8A range of instruments do not have a range of built-in detectors but are ordered either as temperature-programmed instruments with thermal conductivity detection (TCD), flame ionisation detection (FID), or flame photometric detectors (FPD) detectors or as isothermal instruments with TCD, FID, or electron capture detectors (ECD) (Table 5.1). 

FIA-FLD flow injection analysis with fluorescence detection, GC gas chromatography, MS mass spectrometry (quadrupole mass filter), BCD electron capture detector, FID flame ionisation detector, LOD limit of detection, HPLC high performance liquid chromatography, TIMS ion trap mass spectrometry... 

Gas chromatography, coupled with flame-ionisation, electron capture (for halogenated species) and mass spectrometric detectors, is the most popular tool for determination of SVOCs in melted snow samples [44]. A prerequisite is the efficient separation of the analytes from the aqueous matrix, which can be accomplished using filtration onto quartz fibre filters and sohd phase extraction [88]. Solid phase micro-extraction, which utilises equihbrium-based adsorption of analytes onto a polymer fibre bundle, has also been proposed and tested in laboratory studies [13, 89]. Both methods allow for an efficient transfer into the injection port of a gas chromatograph without water contamination. Directly coupled inlet sampler with GC-EID instrumentation has also been used [90]. The air sample was pre-concentrated using adsorbents (Carbotrap B, Carbosieve), followed by heating and collection on a cryofocuser (a fused silica capillary tube packed with... 

ECD (1) Electron-capture detector ESIMS, Electrospray ionisation mass... 

GC is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. In gas chromatography, the mobile phase is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal column. Devices reported for simple quantification or aromatic amine peaks in GC include flame ionisation, nitrogen-selective, flame photometric and electron capture detectors. 

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