Quantitation of bioresmethrin, a synthetic pyrethroid grain protectant, by enzyme immunoassay

Abstract

An enzyme immunoassay was developed for the synthetic pyrethroid, bioresmethrin, by use of a novel approach for synthesis of the pyrethroid-protein hapten conjugate for antibody preparation. Bioresmethrin was hydrolyzed at the ester linkage, and following protection of the chrysanthemic acid group, the 2-methylprop-1-ene substituent was oxidatively cleaved. The newly formed and unprotected acid group was reesterified to the other bioresmethrin hydrolysis product [[2-(phenylmethyl)-4-furyl]-methanol], and following substitution of the protecting group, the hapten was coupled to either protein for antibody production or peroxidase for use in the immunoassay. The most sensitive assay employed an antibody prepared to a derivative with a 4-carbon spacer arm between bioresmethrin and carrier protein, but used a bioresmethrin-enzyme reporter prepared using a 4-(aminomethyl)cyclohexane-carboxylic acid spacer arm (limit of detection 2 ppb in buffer, 50 ppb in whole wheat or barley grain). Good correlations between HPLC and ELISA determinations of bioresmethrin in whole or ground barley grain were obtained. The sensitivity of the assay was slightly lower in ground grain or flour milling fractions due to interference from coextractives in methanol extracts. Apart from resmethrin, of which bioresmethrin is the 1R,3R-trans-isomer, the assay did not detect a variety of other pyrethroids in commercial use.