A Rapid Method for the Analysis of Diquat and Paraquat in Potatoes

A rapid method was developed for the analysis of paraquat dication (I) and diquat dication (II) as their diene reduction products (ID and IID respectively) in potatoes. Macerated potato tissue was spiked with various levels of the dications, 0.05, 0.5, and 5.0 ppm. The dications were reduced using a sodium borohydride/ethanol reduction procedure with reduction and simultaneous extraction in a single 50 ml glass-stoppered centrifuge tube. The diene reduction products were extracted into hexane and analyzed by gas-liquid chromatography (GLC) and a N/P-thermionic detector. Quantification by external standard method or internal standard method resulted in recoveries of 35, 38, 48 and 39,42, 64% for diquat and paraquat respectively. When a spiked macerate was well-mixed, recoveries were low due to adsorption; precision was within 5 5.4% (standard deviation). The importance of spiking technique was also illustrated. Upon thorough mixing and equilibration, of diquat spiked potatoes, recoveries were reduced dramatically. Adsorption of the dications and diene reduction products to glassware reduced recoveries and accounted for poorer precision; this latter effect was overcome by prior silanization of the glassware. Modification of existing NaBH4 methods resulted in a procedure for I and II analysis requiring only 30 minutes per sample for complete analysis. Use of NaBH4 reduction and analysis of I in potatoes has not been previously reported.