Simultaneous Electrochemical Determination of Dopamine and Epinephrine with a Silver-Doped Poly(L-Glutamic Acid) Modified Electrode

In this paper, a silver-doped poly(L-glutamic acid) modified electrode (PLG-Ag/GCE) was fabricated by electrochemical modification of a glassy carbon electrode (GCE) surface. The modified electrode was used to detect dopamine (DA) and epinephrine (EP) in the presence of high concentration of ascorbic acid (AA). In cyclic voltammograms obtained at the modified electrode the cathodic peak potentials of DA and EP in the presence of AA were separated by about 389 mV in phosphate buffer solution (PBS) of pII 7.5 and AA did not interfere with the measurement of DA and EP. The peak separation distance was large enough to determine DA and EP individually and simultaneously. Detection limit of DA in the presence of AA was 5.0 x 10(-7)mol L-1 and the cathodic current of DA increased linearly with the increase of its concentration from 5.0 x 10(-6) to 1.0 x 10(-4) mol L-1 With a correlation coefficient of 0.9902. Furthermore, the cathodic peak current of EP was proportional to the concentration in the ranges 3.0 x 10(-6)-1.0 x 10(-5) mol L-1 and 1.0 x 10(-5)-1.0 x 10(-4) mol L-1 with the correlation coefficients of 0.9934 and 0.9921, respectively. Detection limit of EP was 8.0 x 10(-7) mol L-1. Practical utility of the PLG-Ag modified electrode was demonstrated by determining DA and EP contents in the injection solution and human urine with satisfactory results.