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

A biosensor based on carbon paste modified with crude extract of zucchini ( Cucurbita pepo) and palladium is proposed for determining hydroquinone in p hotographic developers. This enzyme in the presence of hydrogen peroxide ca talyses the oxidation of hydroquinone to p-quinone from which electrochemic al 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 x 10(-5) to 8.9 x 10(-3), mol l(-1) (r= 0.9995) were obtained. The detec tion limit was 8.3 x 10(-6) mol l(-1) and relative standard deviation was 1 .4% for a solution containing 4.0 x 10(-3) mol l(-1) hydroquinone and 2.0 x 10(-3) mol l(-1) hydrogen peroxide (n = 12). The results obtained for hydr oquinone in photographic developers using the proposed biosensor and those claimed in the labels are in agreement at the 95% confidence level. (C) 199 9 Elsevier Science B.V. All rights reserved.