Gas-Liquid Chromatographic Method for the Analysis of Microencapsulated Ethyl Parathion and Methyl Parathion Insecticides: Collaborative Study

The determination of ethyl parathion in Penncap-E insecticide was studied collaboratively by 14 laboratories. The assay of methyl parathion in Penncap-M insecticide was studied by 8 laboratories. The original method which was adopted official first action for methyl parathion specified dimethoate, which is currently classified as a suspected carcinogen, as the internal standard. The current collaborative efforts were conducted as a supplemental study to evaluate the performance of the new internal standard, bis-2-methoxyethyl phthalate, and to test the gas-liquid chromatographic method for microencapsulated ethyl parathion (internal standard, dibutyl phthalate). The method uses essentially the same grinding and extraction with acetonitrile as the original study. At the 20% methyl parathion level, the standard deviation within laboratories was 0.186%, and among laboratories, 0.737%. Two formulations of ethyl parathion at approximately 16 and 24% were analyzed in replicate on 2 days by the same analyst, and provided excellent agreement within laboratories as well as among laboratories. The standard deviation (pooled) within laboratories was 0.284% and among laboratories, 0.518%. The method has been adopted as official first action.

Reverse phase liquid chromatographic determination of sulfathiazole residues in honey

Sulfathiazole residues were extracted from honey by homogenizing samples in acetone, filtering, and then evaporating the acetone under nitrogen at 40 degrees C. The remaining extract was transferred to a separatory funnel with 1N HCl and ethyl ether. An aliquot of the retained acid layer was screened by using the Bratton-Marshall reaction. If the test was positive, the remaining portion was analyzed directly through a mu Bondapak phenyl column monitored by a UV detector at 254 nm. The mobile phase was potassium phosphate monobasic in 10% acetonitrile adjusted to pH 3.0. Time for elution was 13 min. Average recoveries were 78% at the 0.1 ppm spiking level and 68% at the 1.0 ppm level. The minimum detectable amount was 0.06 ppm based on a spiked sample extract.