Determination of paraquat residues in food crops by gas chromatography

A method is described for determining paraquat residues in lettuce, carrots and onions. The procedure is based on the extraction of the sample with 5N H2SO4 and catalytic hydrogenation of the acid extract. This is followed by column cleanup on alumina and subsequent determination by gas chromatography. Recoveries of paraquat added to lettuce, carrots and onion at 0.5, 0.1, and 0.05 ppm were between 75 to 86%, with maximum standard error of 4%. The lower limit of this method is in the 0.05 ppm range.