Potential interferences in certain pesticide residue analyses from organochlorine compounds occurring naturally in plants.

Abstract

Analytical determination of residual amounts of pesticides applied for the protection of livestock or crops is beset with a multitude of problems resulting from interfering substances. Cleanup procedures attempt to separate and concentrate the sought-for-chemical in usually submicrogram amounts from the thousands of other organic compounds present in the sample extractives. Segregation of the pesticide residue is rarely complete and the final analytical sample still usually contains a mixture of components. When a nonspecific analytical procedure is used, naturally occurring substances can grossly interfere in the determination of the applied chemical. This was clearly shown by Gunther et al. ( 1966) in the determination of organochlorine pesticide residues in plants by total combustion followed by direct potentiomet-ric titration of the released chloride ion. The interfering substances were identified as chloride salts of lecithins, a class of phospholipids universally distributed in all living organisms. These lecithin chlorides accompanied the pesticide residues through all the normal organic-solvent extraction and cleanup procedures and were determined as pesticide in the quantitation step. If the same determinations were made by gas chromatography (Gunther and Barkley 1966), the lecithin chlorides did not interfere since they were nonvolatile.