No abstract

h procedure is described for the determination of S-(2 : 5-dichlorophenylthiomethyl) 00-diethyl phosphorothiolothionate residues in fruit and vegetables. Bromination of the 2 : 5-dichlorothiophenol formed by hydrolysis of the pesticide is carried out in acetic acid. The resulting 2 : 5-dichlorophenylsulphonylbromide reacts with potassium cyanide to form cyanogen bromide, which is determined colorimetrically by Aldridge's method. Plant waxes in the extract are removed with acetonitrile. The procedure is relatively specific for phenkaptone. Other pesticides containing thiophosphoric acid esters interfere slightly; carbon disulphide and hydrogen sulphide do not interfere. The sensitivity of the method is about 5 pg in a 100-g sample, i.e., 0.05 p.p.m. THE organo-phosphorus compound S-(2 : 5-dichlorophenylthiomethyl) 00-diethyl phosphorothiolothionate (phenkaptone) is a persistent acaricide having ovicide properties. Its residues in plant material may be determined in the usual way for organic phosphates, namely, by distilling the extracted residue in zlacuo, converting to phosphate and determining the latter colorirnetrically. This method is not specific, of course, and gives recoveries of between 60 and 70 per cent. In an attempt to establish a more reliable method, we studied a reaction described by Saville.l He observed that thiolgenic compounds, including aliphatic thiols,

As the Higgons & Kilbey method2 did not give satisfactory results with spray mixtures on apples, it has been modified by the use of chromium trioxide in glacial acetic acid for oxidation of chlorbenside to the sulphone before application of the m‐dinitrobenzene colorimetric technique. Recovery of chlorbenside added to apple extracts was 90–98%.

No abstract

No abstract