Determination of epinephrine and dopamine in pharmaceutical formulations using a biosensor based on carbon paste modified with crude extract of cara root (Dioscorea bulbifera)

A biosensor based on carbon paste modified with crude extract of cara root (Dioscorea bulbifera) is proposed for the determination of epinephrine and dopamine in pharmaceutical formulations. After selection of the extraction medium, a crude extract of cars root was used as enzymatic source of polyph enol oxidase (PPO; tyrosinase; catechol oxidase; E.C:1.14.18.1). This enzym e catalyses the oxidation of epinephrine and dopamine to corresponding epin ephrinequinone and dopaminequinone. A voltammetric study was performed by s canning the potential between +0.4 and -0.4 V. This biosensor provides a li near response for epinephrine in the concentration range from 2.0 x 10(-4) to 1.2 x 10(-3) mol L-1 at E-pc = -0.14 V (electrochemical reduction of epi nechrome to epinephrine) and for dopamine in the concentration range from 2 .0 x 10(-3) to 8.0 x 10(-3) mol L-1 at E-pc = +0.15 V (electrochemical redu ction of dopaminequinone to dopamine). The detection limit (three times the signal blank/slope) was 8.2 x 10(-5) mol L-1 and 7.5 x 10(-4) mol L-1 for epinephrine and dopamine, respectively. The accuracy was checked by compari ng with a Pharmacopoeia procedure and a paired-t test showing that all resu lts obtained for these catecholamines in pharmaceutical products are in agr eement at the 95% confidence level. The new biosensors have a longer lifeti me than those prepared from purified enzyme.