SIMULTANEOUS DERIVATIVE VOLTAMMETRIC DETERMINATION OF DOPAMINE AND ASCORBIC ACID WITH THE PRUSSIAN BLUE MODIFIED CARBON BLACK MICRO-ELECTRODE

The prussian blue modified carbon black micro-electrode was prepared in two steps.In the 1st step,carbon black,which contains 1.0% (mass percentage) of prussian blue,was mixed with solid paraffin in the ratio of 2.5 to 1 by mass,then in the 2nd step,the carbon black-prussian blue-paraffin mixture was filled into a quartz capillary of  0.2 mm,and a platinum wire was inserted into the upper end of the capillary and polished.The electrochemical behaviors of dopamine (DA) and ascorbic acid (VC) and the optimun conditions for their determinations were studied in detail.The 2nd derivative-linear-scanning voltammetry was used in the quantification of DA and VC.Under the optimum conditions linear relationships between the peak current (i″p) and concentration of DA and VC were obtained in the ranges of 4.0×10-6-8.0×10-4mol·L-1 for DA and 6.0×10-5-1.0×10-3mol·L-1 for VC with their detection limits (3σ) of 2.0×10-6mol·L-1 and 1.0×10-5mol·L-1 respectively.The proposed method has been used for the simultaneous determination of DA and VC in mixed solutions of DA and VC,giving RSD′s less than 3.0% for VC and less than 2.0% for DA and recoveries in the ranges of 95.0%-102.5% and 96.5%-101.0% respectively.