Zucchini crude extract-palladium-modified carbon paste electrode for the determination of hydroquinone in photographic developers Original Research Article

A biosensor based on carbon paste modified with crude extract of zucchini (Cucurbita pepo) and palladium is proposed for determining hydroquinone in photographic developers. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-quinone from which electrochemical reduction back to hydroquinone was obtained at a peak potential of − 0.18 V. The recovery of hydroquinone from two samples ranged from 98.8 to 103.8% and a rectilinear calibration curve for hydroquinone concentration from 6.2 × 10−5 to 8.9 × 10−3 mol l−1 (r = 0.9995) were obtained. The detection limit was 8.3 × 10−6 mol l−1 and relative standard deviation was 1.4% for a solution containing 4.0 × 10−3 mol l−1 hydroquinone and 2.0 × 10−3 mol l−1 hydrogen peroxide (n = 12). The results obtained for hydroquinone in photographic developers using the proposed biosensor and those claimed in the labels are in agreement at the 95% confidence level.