Oxidative detection of nitrite at an electrocatalytic [Ru(bipy)₂poly-(4-vinylpyridine)₁₀Cl]Cl electrochemical sensor applied for the flow injection determination of nitrate using a Cu/Cd redactor column

An electrochemical sensor developed from a redox polymer [Ru(bipy)₂(PVP)₁₀Cl]Cl (where bipy is 2,2′-bipyridyl and PVP is poly-(4-vinylpyridine)) modified electrode for nitrite detection is described. The modified electrode acts as an efficient electrocatalyst for nitrite oxidation with amplification of electrode current by at least a factor of 3 compared with unmodified electrodes. The electrocatalytic reaction occurs throughout the polymer film in a three dimensional reaction zone and may be classified as an L_k mechanism. The second order rate constant for the cross exchange reaction is 3.02 (±0.20) × 10¹ mol^-1 dm³ s^-1. The sensor is applied to the determination of nitrate in a flow injection apparatus following the heterogeneous reduction of this species to nitrite at a copperised cadmium reductor column. The sensor exhibits a linear response range extending over three orders of magnitude from 1.0 × 10^-5 to 1.0 × 10^-2 mol dm^-3 nitrate with a limit of detection (signal-to-noise = 2) of 5.0 × 10^-6 mol dm^-3. The coefficient of variation for measurement of 1.0 × 10^-3 mol dm^-1 nitrite is 0.42% (n = 20). No passivation of the electrode surface was evident after over 200 repeat determinations. The system was applied to the determination of nitrate in commercial fertiliser compound.