Voltammetric performance and application of a sensor for sodium ions constructed with layered birnessite-type manganese oxide

The preparation and electrochemical characterization of a carbon paste electrode modified with layered birnessite-type manganese oxide for use as a sodium sensor is described. The effects of powder synthesis process (sol–gel and redox precipitation) for birnessite on the electrochemical activity of the sensor was investigated by cyclic voltammetry. The carbon paste electrode modified with birnessite-type manganese oxide that was synthesized by the sol–gel method showed a best electrochemical for sodium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the sodium ions extraction into the birnessite structure. The best voltammetric response was obtained for an electrode composition of 15% (w/w) birnessite oxide in the paste, a TRIS buffer solution of pH 8.0 and a scan rate of 50 mV s−1. A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 7.89 × 10−5 to 3.49 × 10−4 mol L−1 with a slope of 37.5 μA L mmol−1 and a detection limit (3σ/slope) of 3.43 × 10−5 mol L−1 using cyclic voltammetry. Under the working conditions, the proposed method was successfully applied to determination of sodium ions in urine samples.