Development and application of a rapid immunoassay for difenzoquat in wheat and barley products

A sensitive and simple enzyme-linked immunosorbent assay (ELISA) is described for the quantification of difenzoquat (DFQ) in foods using polyclonal antibodies. Two hapten analogues of DFQ with five-carbon spacer arms attached to one of the aromatic rings were synthesized. The resulting antiserum was specific to DFQ. The minimum detection limit was 0.8 ng/mL for beer and 16 ng/g for cereals with an IC50 (50% inhibition of binding) of 0.28 ng/mL in this assay. The recoveries of DFQ spiked at three levels into beer, cereal, and bread ranged from 72% to 101%. The mean intraassay and inter-assay coefficients of variation in this procedure were 4.68 and 6.9% for five commodities spiked at 100 ng/g or ng/mL DFQ, respectively. The ELISA procedure was applied to a limited survey of 13 beers and 12 breads, but no detectable DFQ residue was found.