Modified tubular electrode in a multi-commutated flow system: determination of acetaminophen in blood serum and...

This work describes the construction of a Nafion coated glassy carbon tubular electrode and its use, coupled to a multi-commutated flow system, for the voltammetric determination of acetaminophen in serum and pharmaceutical formulations. The modification of the electrode enhanced the analytical signal intensity and, simultaneously, prevented the electrode surface fouling. The multi-commutated system conferred high versatility to the manifold, allowing it to be easily adjusted to each determination without the need to introduce any physical reconfiguration. The on line enzymatic hydrolysis of acetaminophen, giving rise to 4-aminophenol, allowed the problem of interferences resulting from the oxidation of the matrix serum constituents to be overcome. The method presented a linear range up to 5.0 x 10(-4) mol l(-1) with a detection limit of 1.7 x 10(-5) mol l(-1), a sampling rate of 24 determinations per hour and a repeatability (expressed in relative standard deviation) always lower than 3%. The method was applied to serum samples and pharmaceutical formulations and no statistically significant difference between the results obtained by the proposed method and by the reference methods was found, for a confidence level of 95%.