Determination of the naturally derived insect control agent spinosad in cottonseed and processed commodities by high-performance liquid chromatography with ultraviolet detection

A method is described for the determination of the naturally derived insect control agent spinosad in cottonseed and cottonseed processed commodities (meal, hulls, crude oil, refined oil, and soapstock). The method was validated over the concentration range 0.01-0.1 mu g/g, with a limit of quantitation of 0.01 mu g/g and a limit of detection of 0.003 mu g/g. Residues of the active ingredients in spinosad (spinosyns A and D) were extracted from samples with appropriate organic solvents. The extracting solvents were hexane for cottonseed oil, methylene chloride for soapstock, and 60% hexane/40% acetone for cottonseed, meal, or hulls. An aliquot of the extract was purified by liquid-liquid partitioning and silica solid phase extraction. Spinosyns A and D were determined simultaneously in the purified extracts by reversed-phase high-performance liquid chromatography with ultraviolet detection at 250 nm. Confirmation of residue identity was accomplished by reinjecting the same final solution into the chromatograph under different chromatographic conditions.