Flow injection spectrophotometric determination of hydrogen peroxide using a crude extract of zucchini (Cucurbita pepo) as a source of peroxidase

Abstract

A flow injection (FI) spectrophotometric procedure is presented for determining hydrogen peroxide for pharmaceutical use and in swimming pool water samples. Crude extracts of several vegetables such as peach, yam, manioc, artichoke, sweet potato, turnip, horseradish and zucchini were investigated as the source of peroxidase (donor: hydrogen peroxide oxidoreductase, POD; EC 1.11.1.7). Of these, a zucchini crude extract was found to give highest specific activity and was used directly as the carrier solution. This enzyme catalyses the oxidation of guaiacol in the presence of hydrogen peroxide to tetraguaiacol, which shows strong absorbance at 470 nm. For the optimum extraction conditions found, the peroxidase activity in the crude extract did not vary for at least 5 months when stored at 4 °C and decreased by only 2–3% during an 8 h working period at 25 °C. The recovery of hydrogen peroxide from two samples ranged from 97.8 to 103.0% and a rectilinear calibration curve for hydrogen peroxide concentration from 1.6 × 10^–5 to 6.6 × 10^–4 mol l^–1 was obtained. A detection limit of 2.1 × 10^–6 mol l^–1 and a sample throughput of 32 h^–1 were attained. The relative standard deviations were <0.2% for hydrogen peroxide solutions containing 2.0 × 10^–4 and 4.0 × 10^–4 mol l^–1 (n = 10) and a paired t-test showed that all results obtained for water samples using this FI procedure and permanganate titration agreed at the 95% confidence level.