A method for determining residues of biphenyl, benomyl, carbendazim, 2phenylphenol and thiabendazole is presented. Samples are extracted by refluxing with dilute hydrochloric acid, the biphenyl and 2-phenylphenol being steam distilled and collected for determination separately. Benomyl is converted into carbendazim and both carbendazim and thiabendazole are separated from interfering co-extractives by partitioning with chloroform under acidic and basic conditions. Thiophanate-methyl can also be determined after conversion into carbendazim but the conversion is not quantitative, The fungicides are determined by high-performance liquid chromatography using an ultraviolet spectrophotometric detector.
The application of liquid chromatography to the identification and determination of the active ingredient and the impurities in phenylurea herbicides commonly employed in agriculture is described. Technical materials are dissolved in dichloromethane and chromatographed on microparticulate silica with dichloromethane or dichloromethanemethanol as eluting agent, or on microparticulate silica bonded with octadecyltrichlorosilane with methanolwater as eluting agent. An initial extraction procedure is required for dispersible powders. Detection was by means of ultraviolet absorbance.Substituted phenylurea compounds (urons) are widely used in agriculture as selective herbicides for the pre-or post-emergence control of various weeds. Technical materials and dispersible powders are usually analysed by means of acid or alkali hydrolysis with titration of the liberated aliphatic amine1-3 or a colorimetric determination of the aromatic amine f ~r m e d . ~ Methods based on hydrolysis, however, lack specificity for individual urons, as impurities which may be present will be included in the results for the assay. Gasliquid c h r ~m a t o g r a p h y ~, ~ can be used but suffers from the disadvantage that carefully controlled conditions are required in order to prevent thermal decomposition of the phenylurea, either on the column or during injection. A need therefore exists for a rapid and specific procedure for the determination of these compounds and their impurities in technical and formulated products. Methods have been developed that involve liquid chromatography, a technique first applied to analysis for some urons by Kirkland,' and these methods do not have the shortcomings of the procedures mentioned above. The urons examined are shown in Table I. Experimental Apparatus and ReagentsAll reagents were of analytical-reagent grade unless otherwise specified. The equipment used for liquid chromatography was of modular construction. Solvent delivery. A Waters Associates, Model 6000, constant-volume solvent delivery system was used.Sample injection. A Varian Associates stop-flow injector was used throughout this work. For maximum resolution samples were injected with a standard 10-p1 syringe on to a stainlesssteel fine-mesh gauze fitted on top of the column packing. In order to prevent tailing of peaks, a needle guide was incorporated in the injector so that samples were introduced on to the centre of the column. On-column injection was not employed as it was found that the top part of the column gradually became disturbed, which resulted in a dramatic reduction in efficiency. Silica column.A slurry of LiChrosorb SI 60 5-pm silica packing (E. Merck, Darmstadt) in 2,2,4-trimethylpentane saturated with tetrachloroethylene was prepared. By using pressures of 5000-6000 lb in-2 the slurry was forced with 2,2,4-trimethylpentane into a 150 x 4-6 mm i.d. stainless-steel column fitted with a low dead-volume connector containing a frit of pore size 2 pm. The packed column required a pressure of 600 lb in-2 for a flow-rate of dichlorom...
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