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, us ing High-Performance Liquid Chromatography (HPLC) with fluorescence detecti on (excitation and emission wavelengths fixed at 355 and 465 nm, respective ly). The fluorescent derivative was obtained by condensation reaction with trifluoroacetic anhydride and N-methylimidazole. The method employs 1 mL pl asma samples and gives linear calibration graphs (r = 0.999) over the conce ntration 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 re ceiving the therapeutic dose (Spot-on administration).