Residue analysis of clenbuterol in bovine and horse tissues and cow's milkby enzyme-linked immunosorbent assay

Residue analysis of clenbuterol (CBL) in bovine and horse tissues and cow's milk using enzyme-linked immunosorbent assay (ELISA) with alkaline phospha tase as the label is described. The detection limit of the ELISA establishe d here was 0.1 ng/g (0.1 ppb). Tissue samples were homogenized with 3% meta phosphoric acid and cleaned up by liquid-liquid extraction with ethyl aceta te. After evaporation of the ethyl acetate extract, CBL in the residue was measured by ELISA. Recoveries of CBL were 75 similar to 96% for bovine tiss ues, 74 similar to 98% for horse tissues and 99% for cow's milk. CBL was no t detectable in bovine tissues after the 6th day of withdrawal (usual dose: 0.3 mg/head double dose: 0.6 mg/head), or in horse tissues after the 25th day of withdrawal (1.6 mu g/kg, twice a day, for 11 days). CBL concentratio n in horse plasma fell below the detection limit within 24 hours after the final administration. CBL was not detectable alter 2.5 days of withdrawal i n cow's milk or after 6 hours (usual dose group) or 23 hours (double dose g roup) in cow's plasma.