DETERMINATION OF IVERMECTIN IN BOVINE PLASMA BY COLUMN-SWITCHING LC USING ONLINE SOLID-PHASE EXTRACTION AND TRACE ENRICHMENT

Ivermectin is a potent avermectin anthelmintic, derived from the soil organism Streptomyces avermitilis. Because of its potency, it is administered in very low doses (200 mug kg-1), giving rise to plasma levels in the ppb region, and hence sensitive methods are required for its determination in biological samples. A method is described for the determination of ivermectin in bovine plasma, based on a commercially available C18 column employing a mobile phase composed of acetonitrile-water-isopropanol (40:40:35, v/v/v). Extraction from plasma is carried out on-line using coupled-column technology; switching between the extraction and analytical columns is achieved using a six-port column-switching valve. The method is linear over the range 2-100 ng ml-1 (r = 0.9994) and has a limit of detection of 0.8 ng ml-1 (signal-to-noise ratio = 3). Reproducibility of the method, expressed as the overall mean relative standard deviation, is 6.7% (intra-assay) and 3.8% (inter-assay). The mean recovery of the drug from plasma is 76.4%. The method is simple and economical in its execution and is sufficiently reproducible to obviate the need for an internal standard.