A study of the applicability of steam distillation as a potential tool in determination of pesticide residues
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The present study has involved many pesticides and various analytical techniques characteristic for analysis of pesti- cide residues. A brief description of pesticides, termino- logy and some general analytical principles for this field is therefore given in the introduction. Steam distillation is a separation technique that has occasionally been used to isolate pesticide residues from various substrates and the purpose of this work has been to see if such a technique can offer an alternative to traditional extraction and cleanup methods. For the work a special glass apparatus designed by Veith and Kiwus has been used to systematically study more than• 50 different pesticides. The apparatus provides for water vapour distillation and continuous simultaneous extraction of the condensate with an organic solvent. The extracts obtained have been analyzed by chromatographic techniques without further cleanup. Two types of compounds have been considered (i) those that could possibly be determined directly and (ii) those that could possible be hydrolyzed and determined as aromatic amines~ Twelve organochlorine pesticides were studied and found to be distillable. Most of them could be recovered in yields acceptable for residue work. Recoveries ranging from 71% - 110% were obtained for toxaphene, endosulfan A, dieldrin, heptachlor, lindane, aldrin, DDT and its meta- bolites DDE and TDE, from fortified water and carrot samples in neutral medium. Also among the 17 generally less thermostable organo-phosphorus compounds studied several did distill and could be determined in presence of a vegetable test crop (carrot). Recoveries ranging from 71% - 100% were obtained for bromophos, sulfotep, ethion, tricholoronate and diazinon from fortified water and carrot samples in neutral environ¬ment. Recoveries of 13 fungicides, 2 acaricides and 6 herbicides from fortified aqueous solutions are also presented. ReB, quintozene and tecnazene gave r-e co.ve r Le s of 96%, 101% and 96%, respectively from fortified carrot samples in neutral medium. Diuron and linuron which were converted to 3, 4 - dichloro¬aniline on hydrolysis gave recoveries or 93% and 77% res¬pectively, from alkaline solution after boiling for 3 hours. The applicability of the distillation technique for practi¬cal analytical purposes has been demonstrated for the her¬bicide trifluralin and for the newly introduced fungicide procymidone, for which no residue method has been described in the literature. From these pesticides studied,it can be concluded that steam distillation using Veith - Kiwus apparatus .is pro¬mising as a more general technique for residue analysis. The technique has been found easy to use, is rapid and is reasonably inexpensive. The analysis including carrot samples as a test crop also indicate that cleanup steps can be omitted when analyztng for residue levels of practical importance.