Indirect determination of mercury by inhibition of glucose oxidase immobilized on a carbon paste electrode

An amperometric biosensor for the indirect determination of mercury was developed by inhibition of glucose oxidase immobilized on a carbon paste electrode bulk modified with manganese dioxide 5% (m:m). Optimum conditions for biosensor were found as: operating potential 0.46 V vs Ag/AgCl, enzyme load 0.56 U/mm ² electrode surface, supporting electrolyte: 0.1 M citrate phosphate buffer (pH 7). The current response of the biosensor in hydrodynamic amperometry was linearity dependent on the concentration within 2.0 - 32.5 mg/L Hg (II) with a detection limit of 0.5 mg/L. The enzymatic activity could be fully recovered by exposure of the electrode to a solution of EDTA (0.1 M) for 2 minutes. Minor interferences were caused by Cr ³⁺ and Zn ²⁺. Analytical results of spiked water sample showed a good correlation with determinations by atomic absorption spectrometry where the difference is not statistically significant at 95% confidence level. The sensor yielded a stable and reproducible response more than 2 weeks when stored dry at 4 °C.