THE ELECTROCHEMICAL CHARACTERISTICS OF GO LD ELECTRODE MODIFIED BY THIONINE COVALENTLY BOUND TO SELF-ASSEMBLED CYSTEAMINE MONOLAYER AND ITSELECTROCATALYTIC OXIDATION FOR ASCORBIC-ACID

A gold electrode modified by thionine covalently bound to self-assembl ed cysteamine monolayer (Th-SAM) has been prepared, The electrochemica l properties of this Th-SAM modified electrode was investigated by ele ctrochemical methods, There were two redox couples when it was swept i n the range of - 0.45 similar to+ 0.50 V (vs, SCE) by cyclic voltammet ry As to pH 7.7, the peak potentials were E-pa(1)=214 mV, E-pc(1)=82 m V, E-pa(2)=-75 mV, E-pc(2) =-160 mV, respectively, The participating n umber of proton was 2 for peak 1 and 1 for peak 2 in the pH range betw een 5.0 and 9.0, The surface electron transfer rate constant(k(s)) of peak 2 was 0.02 s(-1). The Th-SAM modified electrode could be successf ully used for the electrocatalytic oxidation of ascorbic acid and the catalytic currents increased linearly with the ascorbic acid concentra tion in the range of 1.0x10(-6)similar to 4.0x10(-3) mol/L, The hetero geneous electron transfer rate constant was about 2. 68x10(-3) cm/s.