Analysis of crops and soils for residues of 2,6‐dichlorobenzonitrile (dichlobenil) and 2,6‐dichlorothiobenzamide (chlorthiamid). I.—Development of method

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Abstract
Methods are described for the analysis of residues of two new herbicides, 2,6‐dichlorobenzonitrile and 2,6‐dichlorothiobenzamide, in crop, soil and water samples. The methods are suitable for the analysis of samples containing the benzonitrile alone or the benzonitrile in the presence of the thiobenzamide.Gas/liquid chromatography (GLC) using electron‐capture detection can be used to dctermine 2,6‐dichlorobenzonitrile at 0·005 μg/ml in soil, crop and water extracts. The thiobenzamide cannot be analysed by GLC directly but is oxidised quantitatively to 2,6‐dichlorobenzonitrile by treatment with alkaline permanganate prior to GLC analysis. The benzonitrile and the thiobenzamide can be separated before the final analysis by partition between hexane and water.Adequate extraction procedures are described as well as clean‐up procedures using oxidation, steam distillation, thin‐layer chromatography or column chromatography.Average recoveries of 2,6‐dichlorobenzonitrile are between 85 and 100 % and of 2,6‐dichlorothiobenzamide between 73 and 100% depending on the sample and the extraction procedure.