Determination of paraquat and diquat in low-moisture food crops using silica column cleanup and liquid chromatography with UV detection.

A sample cleanup method was developed for the determination of paraquat (PQ) and diquat (DQ) in low-moisture food crops. Low-moisture commodities, such as milled dry navy beans, are digested in acid. PQ and DQ are isolated from the digestates by using a 4 g column of preconditioned silica gel. The analytes are concentrated and then determined by liquid chromatography with a silica analytical column, sodium chloride as an ion-pairing re-agent, and acetonitrile as an organic modifier. PD and DQ are determined simultaneously with a diode array UV absorbance detector. Recoveries for PQ and DQ were determined on 3 different fortified low-moisture crops. Fortification levels ranged from 0.01 to 0.30 ppm; average recoveries ranged from 47.5% (DQ) to 95.3% (PQ).