Electrooxidation and amperometric detection of ascorbic acid at GC electrode modified by electropolymerization of N,N-dimethylaniline

The polymer film of N,N-dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N-dimethylaniline (PDMA) film-coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (phi): 0.3 +/- 0.02 mum) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag \ AgCl \ NaCl((sat))) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film-coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (D-s) were estimated by rotating disk electrode voltammetry: D = (5.5 +/- 0.1) X 10(-6) cm(2) s(-1) and D-s = (6.3 +/- 0.2) x 10(-8), (6.0 +/- 0.2) x 10(-8) and (4.7 +/- 0.2) x 10(-8) cm(2) s(-1) for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential-step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 muM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 muM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 muA cm(-2) muM(-1). So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film-coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice.