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Chromatographic scince series - Cazes J.

Cazes J. Chromatographic scince series - Marcel Dekker, 1996. - 1098 p.
ISBN 0-8247-9454-0
Download (direct link): сhromatography1996.pdf
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C. Carbamate and Urea Derivatives
Carbamates are nonpersistent pesticides that exhibit low toxicity for warm-blooded animals and human beings. Depending on the structure (see Fig. 3), quite different pesticidal activity is obtained. N-methyl- (IX) and N,N-dimethyl-carbamates (X) possess insecticidal activity, while W-aryl-carba-mates (XI) show herbicidal activity (66). Introducing a sulfur atom or atoms into the carbamate molecule instead of oxygen atom(s) yields thiocarbamate () herbicides and dithiocarbamate ()
' 0 1 ft
R\ II R\
2 N-C-SR 2 N-C-SR
R/ R/
Figure 3 Carbamates. IX, N-methylcarbamate; X, N^-dimethylcarbamate; XI, W-arylcarbamate; XII, thiocarbamate; XIII, dithiocarbamate.
fungicides. In this section, we concentrate on the analysis of IX-XI; XII and ϲ will be discussed in Section m.D.4.
Carbaryl, bendiocarb, carbofuran, baygon, ziram, zineb, and aldicarb were separated on silica gel G layers impregnated with 1% zinc acetate. Zinc sulfate, cadmium acetate, and manganese acetate were studied as impregnants, but the best resolution was observed on the above-mentioned zinc acetate-containing support, /fy-values are summarized in Table 4. The detection of these pesticides was carried out by cesium sulfate in 60% sulfuric acid solution (67).
Eight carbamate pesticides were analyzed in bovine rumen. The method was based on extraction, partition, and an additional sweep condistillation step. This cleanup gave more reproducible results compared to cellulose-carbon column cleanup. The spots were visualized with either anisaldehyde or N,2,6-trichloro-benzoquinoneimine after reversed-phase TLC (68). Carbamate and urea herbicides such as chlorpropham, metobromuron, and chlorbromuron were determined in medicinal plants by TLC. First they were hydrolyzed by alkali to 3-chloro-, 4-bromo-, and 3-chloro-4-bromoanilines. These aniline derivatives were detected with 4-dimethylaminobenzaldehyde after TLC separation (Table 4) (69). N-methyl carbamate pesticides can be separated by reversed-phase chromatography and analyzed by MS (70).
Residues of carboftiran and its metabolite 3-hydroxy-carbofuran were determined in plants, soil, water samples, and artificial diets of Myzuspersicae by GLC and TLC (71). Aldicarb, thiofanox, their sulfoxides, and thiofanox sulfone were investigated in sugarbeet leaves and in artificial diets of Myzus persicae. Interfering materials did not disturb the determination when TLC plates were developed with a mixture of chloroform and acetonitrile (71) (Table 4).
The fate of carbaryl on montmorillonite and in seawater was also studied. This insecticide decomposes in seawater at pH > 8, where a-naphthol forms by a nonbiological pathway. The adsorption and decomposition of carbaryl and its degradation product was studied on montmorillonite. After extraction with acetone, the residues were chromatographed on silica gel F254 with ether-hexane (4:1). The values were 0.55 and 0.73, respectively (72) (Table 4).
Carbaryl is of great importance in pest control in India and in tropical countries. Its selective characterization is important to forensic authorities because in criminal cases this insecticide was used frequently as a poison. A selective detection was described with phenylhydrazine hydrochloride that was mixed with 10% sodium hydroxide solution in (1:1) ratio before spraying the TLC plates. This method is for the detection of carbaryl and its breakdown product 1-naphtol in biological and nonbiological materials (72a) (Table 4).
A simple separation and detection method was published for carbaryl and for the nonsystemic insecticide propoxur. Both pesticides were visualized with diazotized p-nitroaniline (PNA) in alkaline conditions as blue and purple colored spots respectively. Diazotized 6-amino-l-naphtol-3-sulfonic acid (J-acid) detected carbaryl selectivity (72b) (Table 4).
According to another method, carbaryl, carbofuran, propoxur, bavistin, and several nitrophenol derivatives were separated and detected on the TLC plates. The color-forming agent was p-nitroben-zenediazonium tetrafluoroborate, which gave orangish-brown spots on a white background except for carbofuran, which appeared as a purple spot (72c) (Table 4).
Several carbamate insecticides were separated on different supports such as alumina, barium sulfate, cellulose, and silica gel G. Separations of phenols from each other and from carbamate insecticides were reported using different solvents (72d) (Table 4).
A new spray reagent, dapsone, was described for the detection of baygon, carbaryl, and carbofuran. The detection was based on the alkaline hydrolysis of the carbamates forming the corresponding phenols, which can be reacted in the para position with the diazotized aryl amines. The sensitivities of several diazotized anilines, sulfanilic acid, p-toluidine were compared with dapsone. The limits of the detection were about 0.1 \L% range (72e) (Table 4).
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