Gas electron-capture

Pesticides. Chlorinated hydrocarbon pesticides (qv) are often found in feed or water consumed by cows (19,20) subsequently, they may appear in the milk, where they are not permitted. Tests for pesticides are seldom carried out in the dairy plant, but are most often done in regulatory or private specialized laboratories. Examining milk for insecticide residues involves extraction of fat, because the insecticide is contained in the fat, partitioning with acetonitrile, cleanup (FlorisH [26686-77-1] column) and concentration, saponification if necessary, and determination by means of paper, thin-layer, microcoulometric gas, or electron capture gas chromatography (see Trace and residue analysis). 

Ethylene dibromide Lab method with pumped Tenax absorbent tubes, solvent desorption and electron capture gas chromatography 45... 

EPA. 1997e. Methods and guidance for analysis of water. Method 508.1 Determination of chlorinated pesticides, herbicides, and organohalides by liquid-solid extraction and electron capture gas chromatography. U.S. Environmental Protection Agency, Washington, DC. EPA 821-C-97-001. 

TAetection of the highly potent impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), necessitated an environmental assessment of the impact of this contaminate. Information was rapidly needed on movement, persistence, and plant uptake to determine whether low concentrations reaching plants, soils, and water posed any threat to man and his environment. Because of the extreme toxicity of TCDD, utmost precautions were taken to reduce or minimize the risk of exposure to laboratory personnel. Synthesis of uniformly labeled C-TCDD by Muelder and Shadoff (I) greatly facilitated TCDD detection in soil and plant experiments. For unlabeled experiments it seemed wise to use only small quantities of diluted solutions in situations where decontamination was feasible and to rely on the sensitivity afforded by electron capture gas chromatography... 

Rajagopalan et al. [72] described an electron-capture gas chromatographic assay method for the determination of primaquine in blood. The method involves deriva-tization with heptafluorobutyric anhydride to form the diheptafluorobutyramide derivative after a single extraction at alkaline pH. The derivatives are quantitated by electron-capture gas chromatography. Blood levels of primaquine as low as 8 ng/mL can be measured with good precision. 

Cohen [19] used electron capture gas chromatography to determine traces of dissolved nitric oxide in seawater. Precision and accuracy are, respectively, 2% and 3%. 

Aspila et al. [338] reported the results of an interlaboratory quality control study in five laboratories on the electron capture gas chromatographic determination of ten chlorinated insecticides in standards and spiked and unspiked seawater samples (lindane, heptachlor, aldrin, 5-chlordane, a-chlordane, dield-rin, endrin, p, p -DDT, methoxychlor, and mirex). The methods of analyses used by these workers were not discussed, although it is mentioned that the methods were quite similar to those described in the water quality Branch Analytical Methods Manual [339]. Both hexane and benzene were used for the initial extraction of the water samples. 

Elder [355] determined PCBs in Mediterranean coastal waters by adsorption onto X AD-2 resin followed by electron capture gas chromatography. The overall average PCB concentration was 13 ng/1. 

Picer and Picer [357] evaluated the application ofXAD-2, XAD-4, and Tenax macroreticular resins for concentrations of chlorinated insecticides and polychlorinated biphenyls in seawater prior to analysis by electron capture gas chromatography. The solvents that were used eluted not only the chlorinated hydrocarbons of interest but also other electron capture sensitive materials, so that eluates had to be purified. The eluates from the Tenax column were combined and the non-polar phase was separated from the polar phase in a glass separating funnel. Then the polar phase was extracted twice with n-pentane. The -pentane extract was dried over anhydrous sodium sulfate, concentrated to 1 ml and cleaned on an alumina column using a modification of the method described by Holden and Marsden. The eluates were placed on a silica gel column for the separation of PCBs from DDT, its metabolites, and dieldrin using a procedure described by Snyder and Reinert [359] and Picer and Abel [360]. 

The high sensitivity and selectivity of some gas chromatographic detectors are used to advantage in the measurement of organic mercury compounds. In the simplest approach, methyl mercury is extracted from seawater and converted to the iodide for electron capture gas chromatography [74],... 

Wagner, S.L., L.R. Durand, R.D. Inman, U. Kiigemagi, andM.L. Deinzer. 1991. Residues of pentachlorophenol and other chlorinated contaminants in human tissues analysis by electron capture gas chromatography and electronic capture negative ion mass spectrometry. Arch. Environ. Contam. Toxicol. 21 596-606. 

Webb, R.G. and A.C. McCall. 1973. Quantitative PCB standards for electron capture gas chromatography. Jour. Chromatogr. Sci. 11 366-373. 

Tee et al. [15] described an acetone-hexane extraction procedure followed by electron capture gas chromatography for the determination of down to lpg kg-1 chlorinated phenols in sediments. 

Kerwin et al. [41] determined methyl bromide soil fumigant by cyrotrapping and electron capture gas chromatography. Down to 0.23pM of methyl bromide could be detected by this procedure. Kerwin et al. [41] found levels of methyl bromide in the stratosphere and claimed that this contributed to ozone destruction. 

The electron capture gas chromatographic and ETISA procedures described in section 5.6.1.1 have been applied to the field determination of polychlorobiphenyls in sediments [46]. 

Alford Stevens et al. [49] have reported on an inter-laboratory study of the determination of polychlorinated biphenyls in environmental sediments. Electron capture gas chromatography and mass spectrometry were used to identify and determine polychlorinated biphenyls. For electron capture, an overall standard deviation of 30% was achieved while mass spectrometry gave 38%. 

Bertoni et al. [70] used electron capture gas chromatography to determine 2,3,7,8-tetrachlorodibenzo-p-dioxin in Sevesco soil at the pbb level with a 15% standard deviation. 

Abbott et al. [163] described a pyrolysis unit for the determination of Picloram and other herbicides in soil. The determination is effected by electron capture-gas chromatography following thermal decarboxylation of the herbicide. Hall et al. [164] reported further on this method. The decarboxylation products are analysed on a column (5mm i.d.) the first 15cm of which is packed with Vycor chips (2-4mm), the next 1.05m with 3% of SE-30 on Chromosorb W (60-80 mesh) and then 0.6m with 10% of DC-200 on Gas Chrom Q (60-80 mesh). The pyrolysis tube, which is packed with Vycor chips, is maintained at 385°C. The column is operated at 165°C with nitrogen as carrier gas (110ml min-1). The method when applied to ethyl ether extracts of soil gives recoveries of 90 5%. Dennis et al. [165] have reported on the accumulation and persistence of Picloram in bottom deposits. 

Downer et al. [212] reported comparable sensitivity with electron capture gas chromatography and specific ion monitoring of characteristic ions of residues of these compounds in soils. For both herbicides, the detection limit was reported to be 50pg, but less clean-up was required for specific ion monitoring than for electron capture gas chromatography. 

The herbicides are estimated in the extract by electron capture gas chromatography. Both of the clean-up methods used are capable of giving good results at the lpg g 1 level but XAD-2 is inadequate for smaller amounts of herbicides in soil. This poor clean-up and the higher variability in recovery shows XAD-2 to be unsuitable for residue determinations. 

Siu et al. [131] derivitized and determined arsenic in marine sediments using electron capture gas chromatography. 

Siu and Berman [163] determined selenium in marine sediments in amounts down to 0.2pg (or 20ng g 1 of sediment) with a precision of 7%. This method is based on the fact that 1,2 diaminobenzene (o-phenylene diamine) and its derivatives react selectively and quantitatively with selenium IV (average accuracy 94 5%) to form piazselenols that are both volatile and stable. Piazselenols can be determined by electron capture gas chromatography. The sediments were digested as follows. A 0.5g sample was placed in a poly(tetrafluoroethylene) pressure decomposition vessel. A... 

Chen S-H, Wu S-M, Kou H-S, et al. 1994. Electron-capture gas chromatographic determination of cyanide, iodide, nitrite, sulfide and thiocyanate anions by phase-transfer-catalyzed derivatization with pentafluorobenzyl bromide. J Anal Toxicol 18(2) 81-85. 

Moseman RF, Crist HL, Edgerton TR, et al. 1977. Electron capture gas chromatographic... 

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