Determination of analgesics in pharmaceutical formulations and urine samples using nano polypyrrole modified glassy carbon electrode

Three analgesics (acetaminophen, acetylsalicylic acid, and dipyrone) were determined electrochemically using nano polypyrrole modified glassy carbon electrode. The cyclic voltammetric behavior of the three analgesics was studied in aqueous acid, neutral, and alkaline conditions. One well-defined oxidation peak each for acetaminophen and acetylsalicylic acid and three oxidation peaks for dipyrone were observed in the cyclic voltammograms. The influence of pH, scan rate, and concentration reveal the irreversible diffusion controlled loss of 4e(-) in acid and neutral media and 2e(-)/1H(+) in basic medium for acetaminophen. In the case of acetylsalicylic acid, 2e(-) and 1H(+) loss in acidic and neutral pH and 2e(-) and 2H(+) loss in basic pH were observed and the oxidation was irreversible and controlled by adsorption. Irreversible removal of 2e(-) and 1H(+) in all pH media was observed for dipyrone and the oxidation was controlled by diffusion. A systematic study of the experimental parameters that affect the differential pulse stripping voltammetric response was carried out and optimized conditions which yield maximum peak current were arrived at. Scanning electron microscopy (SEM) analysis confirms good accumulation of the drugs on the electrode surface. The calibration was made under optimum conditions. The range of study for acetaminophen, acetylsalicylic acid, and dipyrone was 50-250, 40-300, and 100-400 ng/mL and the lower limit of determination was 45, 25, and 70 ng/mL respectively. The suitability of the method for the determination of the three analgesics in pharmaceutical preparations and urine samples was also ascertained.