Construction and analytical application of a biosensor based on stearic acid-graphite powder modified with sweet potato tissue in organic solvents

A biosensor based on stearic acid-graphite powder modified with Sweet potat o (Ipomoea batatas (L.) Lam.) tissue as peroxidase source was constructed a nd applied in organic solvents. Several parameters were studied to evaluate the performance of this biosensor such as stearic acid-graphite powder and tissue composition, type and concentration of supporting electrolyte, orga nic solvents, water/organic solvent ratio (% v/v) and hydrogen peroxide con centration. After selection of the best conditions, the biosensor was appli ed for the determination of hydroquinone in cosmetic creams in methanol. At the peroxidase electrode hydroquinone is oxidized in the presence of hydro gen peroxide and the radical formed was reduced back electrochemically at - 180 mV vs Ag/AgCl (3.0 mol L-1 KCl). The reduction current obtained was pro portional to the concentration of hydroquinone from 6.2 x 10(-5) to 1.5 x 1 0(-3) mol L-1 (r = 0.9990) with a detection limit of 8.5 x 10(-6) mol L-1. The recovery of hydroquinone from two samples ranged from 98.8 to 104.1% an d an RSD lower than 1.0% for a solution containing 7.3 x 10(-4) mol L-1 hyd roquinone and 1.0 x 10(-3) mol L-1 hydrogen peroxide in 0.10 mol L-1 tetrab utylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n = 10 ) was obtained.