Electrooxidation and Amperometric Detection of Ascorbic Acid at GC Electrode Modified by Electropolymerization of N,N‐Dimethylaniline

Abstract

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 (f): 0.3 AE 0.02 mm) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag j AgCl j 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:, (6.0 AE 0.2) Â 10 À8 and (4.7 AE 0.2) Â 10 À8 cm 2 s À1 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 mM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 mM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 mA cm À2 mM À1. 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.

Simple and Sensitive Electroanalytical Method for the Determination of Ascorbic Acid in Urine Samples Using Measurements in an Aqueous Cationic Micellar Medium

“…According to literature, the oxidation process of AA in an aqueous solution with a pH value higher than the first pKa of AA (first pKa 4.17) involves less of a single proton and two electrons. 28 The presence of CPC in solution promotes an increase in the electron transfer for the oxidation of AA (Fig. 1c), as observed by shift at the anodic peak potential of the compound to less positive values (measured peak potential around 0.0 V), as well as an increase in the measured peak current.…”

A new, improved sensor for ascorbate determination at copper hexacyanoferrate modified carbon film electrodes

“…The storability of this new CuHCF film sensor is at least several months in air at room temperature, representing a significant improvement on previously reported ascorbate or AA electrochemical sensors, which either work at a more positive potential than +0.05 V versus SCE [11,14,18,19,[44][45][46] detection limits [18,19,44]. The sensor most similar to that presented here works at +0.05 V versus Ag/AgCl and has a detection limit of 23 lM for AA, and was developed by Kulys et al [16] based on tetracyanoquinodimethane-modified printed graphite electrodes.…”

“…The response to ascorbate at 0.00 and +0.025 V was poor, but at +0.05 V the response was sufficiently good to determine ascorbate in the micromolar range. At higher potentials the sensitivity increased further, but was never better than other existing sensors [14,[17][18][19][20][21]. Therefore, the operating potential was chosen to be +0.05 V. All three types of CuHCF films (deposited by cycling of the potential, galvanostatically and chemically) were calibrated for the ascorbate anion.…”

“…Other amperometric AA sensors include electrodes chemically modified with 7,7,8,8-tetracyanoquinodimethane [16], osmium 2,2¢-bipyridyl poly-4-vinylpyridine chloride complex [17], lanthanum 2,6-dichlorophenolindophenol [18], electropolymerized N,N-dimethylaniline [19], manganese dioxide [20] and a cobalt (II) phthalocyanine doped with iodine for potentiometric determination [21]; a hanging mercury drop electrode [22] was also used to oxidise AA. The electrocatalytic oxidation of AA on conducting polymer electrodes, in particular on polyaniline, has also been studied [23].…”

In-situ functionalization of aniline oligomer onto layered graphene sheet and study of its application on electrochemical detection of ascorbic acidin food samples

“…The amperometric determination of ascorbic acid is based on its electrochemical oxidation, which occurs at high potential at carbon or metal electrodes, however, fouling by oxidation products leads to poor reproducibility [8]. Numerous attempts to decrease the high working electrode potential and improve reproducibility have been made by modifying the electrode surface with various active mediators for the electrochemical oxidation of ascorbic acid.…”