Biosensor based on paraffin/graphite modified with sweet potato tissue for the determination of hydroquinone in cosmetic cream in organic phase

An organic-phase biosensor based on paraffin/graphite modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as the source of peroxidase was developed and used for determining hydroquinone in cosmetic creams. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-quinone which electrochemical reduction back to hydroquinone was obtained at a peak potential of - 0.22 V, The recovery of hydroquinone from two samples ranged from 99.1 to 104.1% and a rectilinear analytical curve for hydroquinone concentration from 7.5 x 10(-5) to 1.6 x 10(-3) M (r = 0.9991) were obtained. The detection limit was 8.1 x 10(-6) M and relative standard deviation was < 1.0% for a solution containing 7.3 x 10(-4) M hydroquinone and 1.0 x 10(-3) M hydrogen peroxide in 0.10 M tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n = 10). The results obtained for hydroquinone in cosmetic creams using the proposed biosensor are in close agreement with those obtained using a Pharmacopoeia procedure at the 95% confidence level. (C) 2000 Elsevier Science B.V. All rights reserved.