Detection of ivermectin residues in bovine liver using an enzyme immunoassay

Abstract

Ivermectin, a member of the avermectin group, is frequently used to control parasites in many food producing animal species. A method for the detection and quantification of ivermectin residues in bovine liver has been developed. Liver samples (4 g) were extracted with acetonitrile and applied to a competitive enzyme immunoassay using a polyclonal antiserum raised in rabbits against an ivermectin-transferrin conjugate. The limit of detection of the assay (mean ± 3s) calculated from the analysis of 24 known negative samples was 1.6 ng g^–1. Intra- and inter-assay RSDs were determined as 8.8 and 14.6%, respectively, using a negative bovine liver sample fortified with 100 ng g^–1 of ivermectin. Four Friesian steers were treated with a pour-on application of ivermectin at a dose rate of 0.5 mg kg^–1 body mass then withdrawn and killed at 7, 14, 21 and 28 d. Livers were removed and ivermectin residue concentrations determined using the proposed immunoassay procedure. Seven days post-treatment the ivermectin liver concentration was determined as 52.7 ng g^–1, decreasing to 4.1 ng^–1 at 28 d. All immunoassay results were confirmed using high-performance liquid chromatography (HPLC). The immunoassay and HPLC results for invermectin ranged from 1 to 58 ng g^–1 and were in close correlation (r = 0.99).