Determination of selamectin in dog plasma by high performance liquid chromatography with automated solid phase extraction and fluorescence detection.

A method is described for the determination of selamectin in dog plasma, using High-Performance Liquid Chromatography (HPLC) with fluorescence detection (excitation and emission wavelengths fixed at 355 and 465 nm, respectively). The fluorescent derivative was obtained by condensation reaction with trifluoroacetic anhydride and N-methylimidazole. The method employs 1 mL plasma samples and gives linear calibration graphs (r = 0.999) over the concentration range studied (0.5-50 ng mL(-1)). Automatic solid phase extraction using the benchmate procedure was used for sample preparation. This method permits the determination of selamectin at levels as low as 0.1 ng mL(-1) and its suitability was demonstrated by a pharmacokinetic study on a dog receiving the therapeutic dose (Spot-on administration).