A Simple Flow Injection System for Amperometric Detection of Ascorbic Acid Using Carbon Paste/Copper Schiff Base Composite Electrode

In this paper, a simple, sensitive, and precise flow injection system was optimized and applied to ascorbic acid determination with a carbon paste electrode modified with the Schiff base copper complex. The modified sensor showed increased sensitivity toward ascorbic acid oxidation with a decrease of oxidation potential by 200 mV. Under optimized flow parameters, working potential, gasket thickness, sample and reaction coil volumes, and flow rate, the developed flow system gave a linear response from 5 to 75 mu mol/L of ascorbic acid. The calculated limit of detection was 4.5 mu mol/L, calculated as 3 sigma/s which corresponds to the absolute value of 40 ng for the 50 mu L sample coil. The precision for six consecutive injections of 5 and 75 mu mol/L ascorbic acid solutions was determined as a relative standard deviation of 5.8 % and 1.5 %, respectively. The flow injection system enabled up to 120 analyses per hour. An optimized flow system was applied to the determination of ascorbic acid in dietary supplements, after simple preparation. The carbon paste electrode, modified by Copper Schiff base complex, was used for electrooxidation of ascorbic acid in a flow injection amperometric system. Physical and chemical parameters of the flow system were optimized. Under optimal conditions the system was successfully applied on ascorbic acid determination in dietary supplements.image