Detection of ivermectin residues in bovine liver using an enzyme immunoassay
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Four Friesian steers were treated with a pour-on application of ivermectin at a dose rate of 0.5 mg kg–1 body mass then withdrawn and killed at 7, 14, 21 and 28 d. Livers were removed and ivermectin residue concentrations determined using the proposed immunoassay procedure.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).