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A potentiometric sensor for determination of hydrochinone

Hydroquinone has a high toxicity and therefore its content must be carefully monitored. The development of new easy-to-manufacture electrodes with the best analytical characteristics, which have a low cost of analysis, is an urgent task. An electrode based on graphite and a composite material consisting of polyurethane (as polymer matrix), graphite powder (to increase the electrical conductivity of the material) and 18-molybdodiphosphate (as a reagent) for hydroquinone determination was proposed. The advantages of polyurethanes for the electrodes modification include high adhesion of the polymer to the electrode surface due to the presence of a large number of polar groups. In addition, its specific properties provide high physical and mechanical properties of the polymer. The molybdenum heteropoly anion of the Wales-Dawson type 18-molybdodiphosphate anion P2Mo18O626- is a strong enough oxidant. The reaction between it and the some reducing agents is almost instantaneous, the recovery proceeds without destruction of P2Mo18O626-, which allows its repeated use. Interaction of P2Mo18O626- with different reducing agents occurs at different acidity of solutions. Thus, varying the pH of the solution allows determining of several substances in a compatible presence. Fine graphite powder in quantity from 50% to 70% was added in composite material to increase the electrical conductivity. P2Mo18O626- was added in an amount of 20% to the total weight of the composite material. The graphite electrode was modified with the synthesized polymer composite material. The main electrochemical characteristics of the proposed electrode are determined. Reduction of P2Mo18O626- with hydroquinone is proceeds in a neutral medium (pH 6). The response time at different concentrations of the hydroquinone is 8 min (at a temperature of 19 °C). This electrode does not have a "memory effect", the relative error is from 1.3 to 1.9%, and the potential deviation is in the range of 3-5 mV. The limit of determination is 2∙10-5 mol/l. The effect of the present substances was evaluated using a constant of selectivity. The proposed electrode has a high selectivity for a large number of inorganic ions. The electrode must be soaked in a solution of 3% hydrogen peroxide for 10 minutes to regeneration.