Covalent modification of glassy carbon electrodes with glycine for voltammetric separation of dopamine and ascorbic acid

Glycine was covalently grafted on to a glassy carbon electrode (GCE) by ami ne cation radical formation in electrooxidation of the amino-containing com pound. Xray photoelectron spectroscopy (XPS) and cyclic voltammetry proved the immobilization of glycine on the GCE. The modified electrode reduced th e overpotentials of dopamine (DA) and ascorbic acid (AA) by approximately 0 .15 V and 0.23 V, respectively, and resolved the overlapping voltammetric r esponse of DA and AA into two well-defined voltammetric peaks in cyclic vol tammetry (CV) or differential pulse voltammetry (DPV), unlike the unmodifie d GCE; this can be used for the simultaneous determination of these species in a mixture. The differential pulse peak current was linearly dependent o n DA and AA concentration in the range 5 x 10(-6) - 8 x 10(-4) mot L-1 and 6 x 10(-5) - 4 x 10(-3) mol L-1, with correlation coefficients of 0.996 and 0.994, respectively. The detection limits (3 delta) for DA and AA were 1.8 x 10(-6) mol L-1 and 2.1 x 10(-5) mol L-1, respectively. The modified elec trode is very sensitive, selective and stable, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory resu lts.