A biosensor based on paraffin/graphite modified with a sweet potato (Ipomoea batatas (L.) Lam.) tissue as the source of peroxidase was developed and used for determining hydrazine in boiler feed water. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-benzoquinone from which electrochemical reduction back to hydroquinone was obtained at a peak potential of −0.22 V. When hydrazine was added it directly inhibited peroxidase, reduced p-benzoquinone to hydroquinone and/or reduced H2O2, decreasing the cathodic peak current proportionally to the increase of its concentration. Recovery of hydrazine from two samples ranged from 98.0 to 104.3% and the reduction current was proportional to the concentration of hydrazine from 7.0 × 10−6 to 1.2 × 10−4 mol L−1 (r = 0.9980), from 2.9 × 10−5 to 2.0 × 10−4 mol L−1 (r = 0.9986), and from 2.9 × 10−5 to 2.9 × 10−4 mol L−1 (r = 0.9988) with detection limits of 5.1 × 10−7, 8.4 × 10−7, and 1.1 × 10−6 mol L−1 for hydroquinone solutions of 5.0 × 10−4, 1.0 × 10−3, and 1.6 × 10−3 mol L−1, respectively. Results obtained for hydrazine in boiler feed water using the proposed biosensor and those obtained by the official method are in agreement at the 95% confidence level.
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Vieira et al. (2002) studied this question.