Extraction and isolation of avermectins and milbemycins from liver samplesusing unmodified supercritical CO2 with in-line trapping on basic alumina

A multi-residue supercritical fluid extraction (SFE) method has been develo ped for the extraction and isolation of eprinomectin, moxidectin, abamectin , doramectin and ivermectin residues from animal liver. Liver samples are m ixed with hydromatrix and packed into a vessel containing 2 g of basic alum ina. The samples are extracted at 100 degreesC using unmodified supercritic al carbon dioxide (SF-CO2) at a pressure of 300 bar and flow-rate of 5.0 1/ min. The analytes are adsorbed in-line on the basic alumina trap, which is later eluted with 4 ml of methanol-ethyl acetate (70:30, v/v). After evapor ating to dryness, sample extracts are derivatised using methylimidazole, tr ifluoroacetic anhydride and acetic acid at 65 degreesC for 30 min. Derivati sed sample extracts are analysed by high-performance liquid chromatography (HPLC) with fluorescence detection. The method was validated using bovine l iver fortified at levels of 4 and 20 mug/kg with the drugs. The mean recove ry ranged between 76 and 97%. The intra- and inter-assay variations showed RSD values <10 and <16%, respectively. The procedure was also applied to ov ine and porcine liver, giving similar results. The limit of quantitation of the method is 2 mug/kg. (C) 2001 Elsevier Science B.V. All rights reserved .