Gs13005

Methocrotophos

Monitor Nemacur

Paraoxon Parathion Parathion-ethyl Phorate

Pirimiphos-ethyl

Pirimiphos-methyl

Prothoate Salithion

Tetrachlorvinphos Velsicol VCS-506

(2-(ethylthio)ethyl)-O,O-dimethyl phosphorothioate diethyl-2-isopropyl-6-methyl-4-pyrimidinyl phosphorothionate O,O-diethyl-O-(2-isopropyl-6-methyl-4-pyrimidyl) phosphorothioate 2,2-dichlorvinyldimethyl phosphate O,O-dimethyl-S-(2-(ethylthio)ethyl) phosphorodithioate

O,O-dimethyl-O-(3,5,6-(triethylchloro-2-pyridyl) phosphorothioate ethyl-S,S-diphenyl phosphorodithiolate thionate O-

ethyl-S,S-diphenyl phosphordithioate

S,S-methylene-O,O,O',O'-tetraethyl phosphorodithioate

O,O-dimethyl-O-2,4,5-trichlorphenyl phosphorothioate

O,O-dimethyl-O-(4(methylthio)-m-tolyl) phosphorothioate ethyl-S-phenylethyl phosphorothiolothionate ethyl-S-phenylethyl phosphorodithioate S-(5-methoxy-2-oxo-1,3,4-thiadazolin-3-yl)-O,O-dimethyl phosphorodithioate dimethyl-cis-2-(N-methoxy-N-methyl-carbamoyl)-1-

methylvinyl phosphate 3-

(dimethyloxyphosphinyloxy)-N-methoxy-N-

methylisocrotonamide

O,S-dimethyl phosphoramidothioate ethyl-4-(methylthio)-m-tolyl isopropyl phosphoramidate

The oxygen analogue of Parathion

O-(4-nitrophenyl phosphorothioate)

O,O-dimethyl-S-(ethylthio)methyl phosphorodithioate

2-diethylamino-6-methypyrimidin-4-yl diethyl phosphorothionate O-(2-diethylamino-6-methylpyrimidin-4-yl)-O,O-diethyl phosphorothioate

2-diethylamino-6-methylpyrimidin-4-yl-dimethyl phosphorothionate O-(2-diethylamino-6-methylpyrimidin-1-yl)-O,O-dimethyl phosphorothioate

O,O-dimethyl-S-N-isopropyl carbamoyl methyl phosphorothiolothionate

2-sulphide of 2-methoxy-4-H-benzo-1,2,3-

dioxaphosphrin trans-2-chloro-1-(2,4,5-

trichlorophenyl)vinyldimethyl phosphate

O-(4-bromo-2,5-diethylchorophenyl)-O-

methylphenyl phosphorothioate

Zyron O-2,4-dichlorophenyl-O-methylisopropyl phosphoramidothioate

Askew et al. [53] have developed an early general method for the determination of organophosphorus insecticide residues and their metabolites in river waters and sewage effluents utilizing gas chromatography. The organophosphorus pesticides vary greatly in their polarity, and the extent of their extraction from aqueous samples is markedly dependent on the nature of the solvent used. Table 9.17 gives a comparison of the efficacies of three solvents in removing these insecticides from water, and it is apparent that a polar solvent such as chloroform is the most generally used. Askew et al. [53] found that most water extracts are sufficiently low in coextractive to require no clean-up for gas chromatographic purposes. The nature of the coextractive will undoubtedly vary with the location from which the samples are taken, and no complete comprehensive clean-up procedure can be recommended. A column containing 1g of Nuchar carbon eluted with chloroform gave the most useful clean-up where this was found to be necessary. The following insecticides are exceptional in being retained by the column described: Azinophos-ethyl, Azinophos-methyl, Coumaphos, Dichlorvos, Maloxon, Menazon, Phosalone and Vamidothion. When these insecticides are encountered a clean-up on alumina [208] or magnesium oxide [209] would be preferable.

The general screening technique developed by Askew et al. [53] is described in full in Fig. 9.10. Stage (a) is applied as a general screening technique, and stage (b) is incorporated only when suspected pesticides are encountered.

Figure 9.11 shows gas chromatographs obtained by Askew et al. [53] on solvent extracts of River Thames water unspiked and spiked

Table 9.17 Extraction of insecticides from aqueous solution by organic solvents

Insecticides

Insecticide extracted (%)

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