Abstract
A method has been developed that permits the qualitative and quantitative determination of a number of chlorinated and phosphate insecticide compounds on tobacco. Extraction with acetonitrile, partitioning into petroleum ether, cleanup on a Florisil column are followed by gas chromatography and determination with the microcoulometric system (halogen) and the thermionic detector (phosphorus). A procedure is presented for the extraction and determination of the thiophosphates and water-soluble metabolites remaining in the acetonitrile-water layer after petroleum ether partitioning. Carbamate insecticides are extracted with methylene chloride, partitioned into water, separated by thin-layer chromatography, identified and estimated by colourimetry. Recoveries of the compounds (diazinon, parathion, Guthion, malathion, dimethoate) from tobacco fortified just prior to extraction ranged from 74 to 104 %; DDVP, Dipterex, Metasystox R 50 to 78 %, aldrin, DDT, lindane, thiodan 88 to 101 %, carbaryl, Unden 75 to 82 %, at levels of 0.5 ppm. The results for the field application of these 14 different insecticides on tobacco are presented. They show that there are nil or negligible residues from 8 organophosphorus and 1 carbamate insecticides (Unden); carbaryl and thiodan are well below the legal tolerances. Only the treatment of tobacco with lindane, DDT and aldrin (soil treatment) results in residues above the limit set