Laboratory of Forensic Toxicology of the Institute of Legal Medicine of Coimbra, University of Coimbra, 3000 Coimbra, Portugal
* Laboratory of Forensic Toxicology of the Institute of Legal Medicine of Santiago de Compostela, University of Santiago de Compostela, c/ San Francisco s/N, Santiago de Compostela, Spain

The authors describe two methods of parathion determination in liver, kidney and heart from analyte-free tissues and compared their accuracy and precision. All tissue samples were fortified to parathion concentrations of 0.01, 0.1, 1.0 and 10.0 mg/g. The extraction was carried out by hexane. In one of the methods (Method A), the clean-up was performed by solvent partitioning and by column chromatography with florisil. In the other (Method B), the clean-up was carried out by thin-layer chromatography. Gas chromatography was used in the identi-fication and quantification of parathion in both methods.

In method A a higher recovery rate (70.2 % to 79.0%) than in method B was generally obtained. However, in the latter one the lowest concentration presented better results in all the tissues, specially in the liver (80.4%). In the remaining concentration levels the recoveries vary from 68.7% to 78.1%. The coefficients of variation were 8.2% and 8.7% with ranges of 4.3% to 11.1% and 4.5% to 10.0% for methods A and B, respectively.

Although, in general, method A presents better results, method B, being simpler, is the one used in undertaking routine analyses for parathion determination, except in cases where the samples have a great deal of fat, since the insecticide may not be well differentiated from the fat in these cases.