Phosdrin Residues in Fruits and Vegetables

The enzyme inhibition-spectrophotometric procedure for Phosdrin residues submitted by the manufacturer has been slightly modified and studied collaboratively on apples, tomatoes, and cabbages. This method is based on the ability of Phosdrin to inhibit cholinesterase. Phosdrin is extracted from crops with chloroform, transferred into water, purified to remove organic impurities, and determined quantitatively by the acetylcholinesterase inhibition procedure. The uninhibited cholinesterase hydrolyzes acetylcholine to acetic acid and choline. The acetylcholine not hydrolyzed is reacted with alkaline hydroxylamine and a ferric salt to form a red complex, the absorbance of which is measured spectrophotometrically at 540 mμ. The recoveries at the 0.164 and 0.328 ppm levels of addition ranged from 73.2 to 109.8% for apples, 70.1 to 111.0% for tomatoes, and 68.9 to 117.0% for cabbages. The mean recoveries for apples, tomatoes, arid cabbages were 95.9, 94.9, and 91.6%, respectively; the over-all recovery was 94.1%. The method is recommended as official, first action for quantitative determination of Phosdrin residues in fruits and vegetables.