Identification electron capture

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

An ion mobility spectrometer offers to prospective users an attractive detector for a GC, from the perspective of detection limits and specificity. A mobility spectrometer, even with low resolution, allows interrogation of compound identities and imparts better specificity than the electron-capture detector. When gaseous analytes are delivered individually to IMS, the mobility spectrum contains information for identification, provided that operating conditions are kept constant for the unknown and reference spectra. The connection of a GC column to an ion mobility spectrometer is... 

The electron capture detector (ECD) is most frequently used to identify hexachloroethane. A flame ionization detector (FID) may also be used (NIOSH 1994). When unequivocal identification is required, an MS coupled to the GC column may be employed. 

In recent years, a novel approach to protein identification emerged, called top-down sequencing. Here the entire nondigested protein is analyzed. Apart from accurate MW measurement, the protein ion is fragmented by the electron capture dissociation (ECD) method (see Chapter 3). This provides in-depth information on the sequence of protein. Such analysis can be performed only with FTICR instruments (see Section 2.2.6) that ensure high resolution and accuracy but, at the same time, they are exceptionally expensive. However, as very large ions are analyzed, even the high accuracy of FTICR is sometimes not sufficient, and it is recommended that such analyses are accompanied by more traditional bottom-up approaches. 

Gooding et al. [9] used DDT-dehydrochlorinase for the identification of DDT in soils. The enzyme converts DDT to DDE which is then determined gas chromatographically on Chromosorb WHMDS at 190°C using an electron capture detector. 

The best sensitivity for 1,2-dibromoethane quantification is obtained by either electron capture detector (ECD) or Hall electrolytic conductivity detector (HECD) in the halide detection mode, since these detectors are relatively insensitive to nonhalogenated species and very sensitive to halogenated species. Another common detection device is a mass spectrometer (MS) connected to a GC. The GC/MS combination provides unequivocal identification of 1,2-dibromoethane in samples containing multiple components having similar GC elution characteristics (see Table 6-2). To date, GC equipped with either ECD or HECD has provided the greatest sensitivity for detecting... 

Analytical methods exist for measuring heptachlor, heptachlor epoxide, and/or their metabolites in various tissues (including adipose tissue), blood, human milk, urine, and feces. The common method used is gas chromatography (GC) coupled with electron capture detection (ECD) followed by identification using GC/mass spectrometry (MS). Since evidence indicates that heptachlor is metabolized to heptachlor epoxide in mammals, exposure to heptachlor is usually measured by determining levels of heptachlor epoxide in biological media. A summary of the detection methods used for various biological media is presented in Table 6-1. 

MS detectors are unique among GC detectors because they deliver better quantitation of partially resolved peaks as well as improved confidence in peak identification. By their use, even chlorinated compounds like the coccidiostat clopidol can be determined with improved sensitivity and selectivity compared with traditional electron capture detection (20). The amount of the time needed to conduct GC-MS varies, depending upon confirmation or identification tasks. Sample preparation may take between 10 min and 24 h actual testing time may range from 30 min to 8 h, and evaluation between 1 and 40 h. 

The more advanced instrumental methods of analysis, including GC, for the detection and identification of expls are presented (Ref 90) Pyrolysis of expls in tandem with GC/MS was used for the identification of contaminant expls in the environment (Ref 108). Isomer vapor impurities of TNT were characterized by GC-electron capture detector and mass spectrometry (Ref 61). Volatile impurities in TNT and Comp B were analyzed using a GC/MS the GC was equipped with electron capture and flame ionization detectors (Ref 79). The vapors evolved from mines, TNT, acetone, toluene, cyclohexanone and an organosilicon, were analyzed by GC/MS (Ref 78). Red water produced by the sellite purification of crude TNT was analyzed by GC/MS for potentially useful organic compds, 2,4-dinitrotoluene, 3- and 4-sulfonic acids (Ref 124). Various reports were surveyed to determine which methods, including GC/MS, are potential candidates for detection of traces of TNT vapors emitted from land mines factors influencing transportability of TNT vapors thru soil to soil/air interface are dis-... 

Y. V. Gankin, A. E. Gorshteyn and A. Robbat-Jr, Identification of PCB congeners by gas chromatography electron capture detection employing a quantitative structure-retention model , Anal. Chem. 67 2548-2555 (1995). 

It is obvious that unequivocal identification of small quantities of ABA can only be accomplished by combined gas chromatography-mass spectrometry. However, once this has been accomplished in a particular system, routine measurements will in the future probably mostly rely on gas chromatography with electron capture detector and on radioimmunoassay. 

J. M. Moore and M. Klein, Identification of 03-monoacetyl-morphine in illicit heroin by using gas chromatography-electron-capture detection and mass spectrometry, J. Chromatogr., 154 16... 

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