Dual electrochemical quantitative analysis of dopamine based on flow injection amperometry with double glassy carbon electrodes

A simple, rapid and stable electrochemical flow injection amperometry (FI-Amp) system based on a flow cell with two glassy carbon electrodes arranged in series was constructed and the redox mechanism of dopamine (DA) was investigated as a research model. Electrochemical oxidation of DA occurs at the surface of the first working electrode (WE1, +0.24 V working potential), and then its oxidation product undergoes electrochemical reduction when it flows through the second working electrode (WE2, +0.05 V working potential). The source of the reduction currents on the WE2 was discussed and finally identified as dopaquinone (DAQ). In addition, dual quantitative analysis of DA was achieved by the oxidation current of DA on WE1 and the reduction current of DAQ on WE2. Under optimized conditions, the dual linear response ranges for DA were from 0.5 µM to 250 µM and 2 µM to 250 µM, and the dual limits of detection were found to be 0.20 µM and 0.68 µM (S/N = 3), respectively. Moreover, the RSDs of the amperometric responses for 5 µM, 50 µM and 200 µM DA were all less than 10% over 50 repeated injections, showing that the FI-Amp system has excellent repeatability and stability. The approach is universal and superior to the traditional three-electrode system. It can be used to study the mechanisms of molecular redox reactions and has great potential for application in the electrochemical identification of other electroactive molecules.