Substituted urea herbicides, determination

Sodium-N-diethyldithiocarbamate, determination of 207 Stilbenzene, determination of 263, 264 Substituted urea herbicides, determination of 314-316 Succinate, determination of 60-65 Sulphate, determination of 51-56, 60-65, 70-75, 77, 87-90,170,199,... 

The gas chromatographic procedure described by Cohen and Wheals [80] has been applied to the determination of various substituted urea herbicides in soil in amounts down to l-50pg kgr1. 

RG Luchtefeld. Multiresidue method for determining substituted urea herbicides in foods by liquid chromatography. J Assoc Off Anal Chem 70 740-745, 1987. 

SE Katz. Determination of the substituted urea herbicides linuron, monuron, diuron, neburon and fenuron in surface waters. J Assoc Off Anal Chem 49 452-456, 1966. 

Cohen and Wheals [334] determined ten hydrolysable carbamate and substituted urea herbicides in soil in amounts down to 0.001-0.05 ppm. In this method, a solution of the herbicide-containing extract of the soil is spotted onto a silica gel G plate and developed with hexane acetone (5 1). The plate is sprayed with 1-fluoro-l,4-dinitrobenzene in acetone and heated to 190 °C to produce the 2,4-dinitrophenyl derivative of the herbicide amine moiety acetone extracts of the areas of interest are subjected to gas chromatography. 

Other applications of gas chromatography to the determination of substituted urea herbicides in non saline water are discussed in Table 15.9. 

Mechanism of action can be an important factor determining selectivity. In the extreme case, one group of organisms has a site of action that is not present in another group. Thus, most of the insecticides that are neurotoxic have very little phytotoxicity indeed, some of them (e.g., the OPs dimethoate, disyston, and demeton-5 -methyl) are good systemic insecticides. Most herbicides that act upon photosynthesis (e.g., triaz-ines and substituted ureas) have very low toxicity to animals (Table 2.7). The resistance of certain strains of insects to insecticides is due to their possessing a mutant form of the site of action, which is insensitive to the pesticide. Examples include certain strains of housefly with knockdown resistance (mutant form of Na+ channel that is insensitive to DDT and pyrethroids) and strains of several species of insects that are resistant to OPs because they have mutant forms of acetylcholinesterase. These... 

This technique has been applied to the determination of chlorinated insecticides, carbamate insecticides and substituted urea type herbicides in soil and chloroaliphatic hydrocarbons in non-saline sediments. Separation is usually achieved on thin layers of silica gel or alumina. 

Spengler and Jumar [90] used a spectrophotometric method and thin layer chromatography to determine carbamate and urea herbicide residues in sediments. The sample is extracted with acetone, the extract is evaporated in vacuo at 40°C and the residue is hydrolysed with sulphuric acid. The solution is made alkaline with 15% aqueous sodium hydroxide and the liberated aniline (or substituted aniline) is steam distilled and collected in hydrochloric acid. The amine is diazotized and coupled with thymol, the solution is cleaned up on a column of MN 2100 cellulose power and the azo-dye is determined spectrophotometrically at 440nm (465nm for the dye derived from 3-chloro- or 3.4-dichloroaniline) with correction for the extinction of a reagent blank. 

The method based on immunosorbents coupled on-line with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry [109], discussed in section 9.4.2.1, has been applied to the determination of substituted urea type herbicides. Supercritical fluid extraction with methanol modified carbon dioxide has been applied to the determinants of sulfonyl urea herbicides in soil [261],... 

Gas chromatography of phenyl urea herbicides is difficult because of their ease of decomposition. Procedures have been reported in which careful control of conditions allows these compounds to be chromatographed intact [339, 340,344,345]. Alternatively, the urns can be hydrolyzed to the corresponding substituted anilines these compounds are then determined by either gas chromatography directly [341] or as derivatives [342], or colorimetrically [343] after coupling with suitable chromospheres. Methods based on hydrolysis lack... 

Cohen and Wheals [185] used a gas chromatograph equipped with an electron capture detector to determine 10 substituted urea and carbamate herbicides in river water, soil and plant materials in amounts down to 0.001-0.05ppm. The methods are applicable to those urea and carbamate herbicides that can be hydrolysed to yield an aromatic amine. A solution of the herbicide is first spotted on to a silica gel G plate together with herbicide standards (5-lOpg) and developed with chloroform or hexane-acetone (5 1). The plate containing the separated herbicide or the free... 

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