Improvements to assisted distillation cleanup of pesticide residues in animal fats.

The assisted distillation technique, which was developed for the cleanup of pesticide residues from animal fats, has been improved. Nitric acid cleaning of distillation tubes resulted in a significant improvement in the recoveries of hexachlorobenzene (HCB) and lindane (from 76 to 92% and 84 to 89%, respectively). A larger U-tube condenser was developed that condensed 100% of all pesticides studied. With this new condenser, a study of distillation tube flow rates showed that pesticide recoveries at 600 mL nitrogen/min were generally better than those obtained at any other flow rate although recoveries were satisfactory at 400 and 800 mL/min. Recoveries of pesticides at distillation temperatures of 210-240 degrees C were obtained with tubes cleaned with nitric acid, and using the larger U-tube condenser. The distillation temperature of choice was again 230 degrees C because there was little variation from 220 to 240 degrees C.