DEVELOPMENT OF A SENSOR FOR THE DETECTION OF NITRITE USING A GLASSY-CARBON ELECTRODE MODIFIED WITH THE ELECTROCATALYST [OS(BIPY)2(PVP)10CL]CL

The electrocatalytic polymer [Os(bipy)2(PVP)10Cl]Cl, where bipy = 2,2'-bipyridyl and PVP = poly(4-vinylpyridine), was used to modify glassy carbon electrodes for use in planar flow cells and conventional electrochemical cells for the reductive electrochemical detection of nitrite. The electrocatalyst accelerates a slow electrochemical reduction of nitrite via a two-step reduction process resulting in a 70-fold increase in response compared with the unmodified electrode. The detector response was evaluated with regard to flow-rate, applied potential, electrolyte pH and surface coverage of the polymer film. A mechanism for the two-step reduction process is proposed. The detector response appears to be limited by the rate constant of the mediated electrochemical reaction. A linear response range extending from 5 x 10(-6) to 1 X 10(-2) M nitrite was obtained, with a detection limit of 0.23 ng ml-1 for the planar flow cell and 0.023 ng ml-1 for a conventional electrochemical cell. The performance of the sensor was assessed with respect to stability, selectivity and interference. The sensor was applied to the determination of nitrite in saliva.