Amperometric determination of hydrazine using a surface modified nickel hexacyanoferrate graphite electrode fabricated following a new approach

A new kind of modified electrode fabricated by attaching nickel hexacyanoferrate (NiHCF) to the surface of an amine-functionalized graphite is proposed. The cyclic voltammogram of the NiHCF modified electrode prepared by this method exhibits a pair of well defined redox peak at scan rates up to 200 mV s(-1) in 0.1 M NaNO3 (pH 7.0) solution. The effect of the supporting electrolyte indicates that the radius of the hydrated cation mainly determines the ion permeability of the film. The effect of the anions of the supporting electrolyte was also studied. The transfer coefficient (infinity), and the electron transfer rate constant (K-s) were calculated in the presence of alkali metal cation. The modified electrode was characterized by electrochemical impedance spectroscopy (EIS) which showed that the tunable kinetic barrier was substantially altered by modifying the electrode with NiHCF. The modified electrode shows good electrocatalytic activity towards the electrochemical oxidation of hydrazine in 0.1 M NaNO3 (pH 7.0). The oxidation current increased linearly with the concentration of hydrazine in the range of 2.4 x 10(-6)-8.2 x 10(-3) M and with a correlation coefficient of 0.9976. The limit of detection was found to be 1 x 10(-6) M. The utility of the developed sensors in dynamic systems was evaluated by hydrodynamic and flow injection analysis (FIA). Differential pulse voltammetry (DPV) and flow injection analysis techniques were also used for determination of hydrazine from standard samples and different water sources chosen for real sample analysis (spiked with hydrazine). The developed sensor showed excellent stability for long time usage, higher sensitivity and was economical to fabricate. (C) 2008 Elsevier B.V. All rights reserved.