Determination of phenylbutazone and flunixin meglumine in equine plasma by electrochemical-based sensing coupled to selective extraction with molecularly imprinted polymers

Phenylbutazone and flunixin meglumine are non-steroidal anti-inflammatory drugs with antiinflammatory and analgesic activities widely used for the treatment of bone and joint inflammations, laminitis and soft tissue inflammation in the horse. The aim of the present study was to develop a new, selective, sensitive and fast analytical approach for phenylbutazone and flunixin quantitative detection in equine plasma. Differential pulse voltammetry experiments were performed with a portable electrochemical transducer by using miniaturized disposable graphite based screen-printed electrodes. The electrochemical detection by differential pulse voltammetry was coupled to prior selective extraction using dedicated molecularly imprinted solid phase extraction (MISPE) columns to reduce/avoid possible interferences present in plasma. Recovery after MISPE for both phenylbutazone and flunixin was >96%, with intra-day values below 5.0% and inter-day values below 6.5%. Method limit of quantification was 0.01 μg/ml for both phenylbutazone and flunixin. The results obtained with DPV method showed a good correlation with those provided by an HPLC reference method. The method can be proposed as a suitable alternative to the existing chromatographic methods for the determination of phenylbutazone and flunixin in equine plasma samples.