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

An organic-phase biosensor based on paraffin/graphite modified with sweet p otato (Ipomoea batatas (L.) Lam.) tissue as the source of peroxidase was de veloped and used for determining hydroquinone in cosmetic creams. This enzy me in the presence of hydrogen peroxide catalyses the oxidation of hydroqui none 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 = 0.9 991) were obtained. The detection limit was 8.1 x 10(-6) M and relative sta ndard deviation was < 1.0% for a solution containing 7.3 x 10(-4) M hydroqu inone and 1.0 x 10(-3) M hydrogen peroxide in 0.10 M tetrabutylammonium bro mide methanol-phosphate buffer solution (95:5% v/v) (n = 10). The results o btained for hydroquinone in cosmetic creams using the proposed biosensor ar e in close agreement with those obtained using a Pharmacopoeia procedure at the 95% confidence level. (C) 2000 Elsevier Science B.V. All rights reserv ed.