Application of Nafion/cobalt hexacyanoferrate chemically modified electrodes for the determination of electroinactive cations by ion chromatography

An amperometric detector based on the chemical modification of Nafion and cobalt (II) hexacyanoferrate (II, III) thin film (Nafion/Co-CN-Fe) onto a glassy carbon (GC) electrode was firstly developed for the determination of electroinactive cations (Li⁺, Na⁺, K⁺, Rb ⁺, Cs⁺ and NH₄⁺) in single column ion chromatography. A set of well-defined peaks of electroinactive cation was obtained. The relative standard deviations (RSDs) of Chromatographic peak height (nA) for these cations were all below 3.8%. The cations were detected conveniently in the linear concentration range of 6.0 × 10 ^-6-5.0 × 10^-3 mol/L and their correlation coefficients were all above 0.99. The detection limits of the cations were 9.2 × 10^-6 mol/L for Li⁺, 3.4 × 10^-6 mol/L for Na⁺, 6.3 × 10^-7 mol/L for K⁺, 7.8 × 10^-7 mol/L for Rb⁺, 6.2 × 10 ^-7 mol/L for Cs⁺ and 6.2 × 10^-6 mol/L for NH₄⁺, at a signal-noise ratio of 3. The method was quick, sensitive, simple and was successfully applied to the analysis of rainwater samples. The electrode was stable for a 2 week period of operation with no evidence of chemical or mechanical deterioration.