[Os(bpy)(2)(PVP)(10)Cl]Cl polymer and Nafion dual-film modified graphite electrode for the amperometric determination of trace amounts of norepinephrine

A chemically modified graphite electrode was prepared by using a dual film of [Os(bpy)(2)(PVP)(10)Cl]Cl polymer and Nafion. The modified electrode showed excellent electrocatalytical activity for the oxidation of norepinephrine (NE) and an ability to eliminate efficiently the interference of ascorbic acid and other anions. The catalytic peak currents obtained from the cyclic voltammograms increased linearly with increasing concentration of NE. A log-log plot of catalytic current versus NE concentration showed a dual-linear relationship in the ranges 1.8 x 10(-8)-4.4 x 10(-6) M and 4.3 x 10(-6)-2.9 x 10(-4) M with correlation coefficients of 0.990 and 0.999, respectively. The detection limit was about 18 nM (3 sigma). At a potential of +500 mV the chronoamperometric response showed a linear relationship between the steady state current and NE concentration in the range 1.3-130 mu M. With a further increase in NE concentration a Michaelis-Menten-shaped response was observed. The apparent Michaelis-Menten constant and the maximum current were 1.7 mM and 86 mu A, respectively. The modified electrode showed excellent reproducibility, sensitivity and stability for the determination of NE at trace levels.