Ascorbic acid cyclic voltammograms

Figure 3. Cyclic voltammograms of ascorbic acid at a freshly polished, active (a) and a deactivated (b) glassy carbon electrode surface. See text for details.

Figure 6. Simulated cyclic voltammogram for the oxidation of ascorbic acid without Inclusion of ec catalysis by the surface qulnone functionalities. Filled circles represent the simulated data and an experimental curve Is shown with a line for comparison. A scan rate of 100 mV s was assumed for experimental and simulated data.

Figure 3.19 Cyclic voltammogram obtained with an arc-CNT-modified electrode in the presence of 5 mM ascorbic acid, (a) before and (b) after electrochemical activation at 1.5 V for 3 min in PBS solution, scan rate lOOmV/s. Adapted with permission from Ref [133]. Copyright, 2005, Elesevier.

Fig. 8.8. Cyclic voltammograms obtained (a) with a platinum microelectrode in a deaerated phosphate buffer solution (—) or in a deaerated ascorbic acid ImmolL-1 and uric acid lmmolLT1 solution (—) and (b) with a gold microelectrode in a deaerated phosphate buffer solution (—) or in a deaerated glutathione ImmolL-1 solution (—). Potential scan rate 50mVs-1.

Fig. 14.4. Cyclic voltammograms for (A) 1 mM K4Fe(CN)6 in 1M KC1, (B) 1 mM Ru(NH3)6C13 in 1M KC1, (C) ImM Fe(C104)3 in 1M HC104, and (D) lmM ascorbic acid in 1M HC104 at (dotted line) as-deposited and (bold line) an-odically oxidized diamond electrodes, respectively. The potential sweep rate was 0.1 V s 1.

Figure 12.4 Cyclic voltammograms in dimethylformamide (0.1 M tetraethylammon-ium perchlorate) of 2 mM ascorbic acid (H2A), 2 mM HA- (from 2 mM H2A and 2 mM TEAOH), 2 mM dehydroascoibic acid (A), and the product from the one-electron reduction of 2 mM A at —1.2V versus SCE. Measurements were made with a platinum electrode (area 0.23 cm2) at a scan rate of 0.1 V s-1, temperature 25°C NHe = sce + 0.244 V.

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

Fig. 32. Cyclic voltammograms for a 0.1 M HCIO4 solution containing 0.1 mM dopamine (DA) + 1 mM ascorbic acid (AA) at untreated (dashed line) and oxidized (solid line) diamond electrodes. Potential scan rate 100 mV s 1 [148], Reproduced by permission of The Electrochemical Society, Inc.

The ECSOW system has also been applied to a biomimetic redox system, i.e., the oxidation of L-ascorbic acid in W by chloranil added to NB [38]. A comparison of the cyclic voltammograms obtained with the ECSOW system and the O/W interface has provided important suggestions on the possible reaction mechanism at the OAV interface. Thus, the ECSOW system would offer important clues to clarify ET processes at O/W interfaces. 

It is evident from these considerations that the use of a less hydrophobic redox species in the O phase makes the homogeneous ET occur more favourably. Another example of the IT mechanism has been found in the ET between L-ascorbic acid in W and chloranil (with Ko = 900) in NB or DCE. This has been confirmed using potential-controlled polarography [47], potential modulated reflectance spectroscopy [46], microflow coulometry [39], ECSOW system [38] and digital simulation of cyclic voltammograms [48]. 

Figure 6.6.5 Application of cyclic voltammetry to in vivo analysis in brain tissue, (a) Carbon paste working electrode, stainless steel auxiliary electrode (18-gauge cannula), Ag/AgCl reference electrode, and other apparatus for voltammetric measurements, (b) Cyclic voltammogram for ascorbic acid oxidation at C-paste electrode positioned in the caudate nucleus of an anesthetized rat. [From P. T. Kissinger, J. B. Hart, and R. N. Adams, Brain Res., 55, 20 (1973), with permission.]...

Figure 17.9 Cyclic voltammograms of electrochemical oxidation of ascorbic acid (A) a planar film composed of PAN/Au-NPs (B) a planar film composed of PAN/PSS (C) a bare Au electrode, in different concentrations of ascorbic acid (a) 0 mM, (b) 5 mM, (c) 10 mM, (d) 20 mM, (e) 30 mM, and (f) 40 mM. The data were recorded in 0.1 M phosphate buffer, pH 7.5. Oxygen was removed from the background solution by bubbling Ar. Potential scan rate, 5 mV s (Reprinted with permission from Chemistry of Materials, Enhanced Bioelectrocatalysis Using Au-Nanoparticle/Polyaniline Hybrid Systems in Thin Films and Microstructured Rods Assembled on Electrodes by E. Granot, E. Katz, B. Basnar and I. Wiliner, 17, 18, 4600—4609. Copyright (2005) American Chemical Society)...

Figure 10.2 Cyclic voltammogram of oxidation of 2.5x10" m dopamine in the presence of 100-fold excess of ascorbic acid, in phosphate buffer, pH = 7, obtained on (a) bare carbon fibre microdisc electrode and (b) the same electrode modified with semipermeable membrane poly(4-HBS/2-AP) (100 1). Curves ( ) were obtained in the background electrolyte (phosphate buffer, pH = 7).

Fig. 7.9 (a) Differential pulse voltammograms for a zeolite-modified electrode (ZME) after deposition of 1 ppm Ag" solution for different pre-concentration times (a) 1 (b) 2 (c) 3 (d) 5 (e) 10 min (Reproduced from Ref. [132] with permission of Elsevier), (b) Cyclic voltammograms of 2 X lO " M (a) dopamine and (b) ascorbic acid at (1) pure and (2) 10 wt.% zeolte-modified carbon paste electrodes (Reproduced from Ref. [133] with the permission of Elsevier)... 

Agboola et al. [57] reported the utilization of phenylamine-modified SWCNTs integrated with cobalt(II) octa[(3,5-biscarboxylate)-phenoxy] phthalocyanine (CoOBPPc) for (5-nicotinamide adenine dinucleotide (NADH) detection (Fig. 10a). The sensor showed good ability to detect low concentrations of NADH even in the presence of high concentration of ascorbic acid, which frequently interferes in the electrochemical determination of this analyte. Comparative cyclic voltammograms at bare GC and CNTs-modified electrode can be seen in Fig. 10b. 

Fig. 10 a Synthetic route for the preparation of CoBCPPc/SWCNT-phenylamine hybrid material b Comparative cyclic voltammograms at bare GC electrode for 10 mM ascorbic acid (i) and a mixture 0.5 mM NADH + 10 mM ascorbic acid (ii), and at CoBCPPc/SWCNT-phenylamine electrode for 10 mM ascorbic acid (iii) and a mixture 0.5 mM NADH + 10 mM ascorbic acid (iV). Reprinted with permission from [57]. Copyright (2010) Elsevier... 

Fig. 19 a CuTsPc entrapped in the pores of porous 3-n-propylpyridinium silsesquioxane functionalized Si02/Al203 and b cyclic voltammograms of SiAl/SiPy and SiAl/SiPy/CuTsPc in the presence of ascorbic acid 2.3 mM. Reprinted with permission from [70]. Copyright (2002) Taylor Francis... 

Fig. 2.35 a Cyclic and b differential pulse voltammograms of 0.1 mM ascorbic acid and 0.1 mM acetaminophen in acetate buffer solution (0.1 M, pH 4.0) on the surface of various electrodes unmodified carbon paste electrode (solid line), CNT-carbon paste electrode (dotted line) and multi-walled carbon nanotube/thionine modified electrode (dashed line). Sweep rate was 100 mV s. Reproduced from Ref. [19] with permission of Elsevier... 

Fig. 11.3. Cyclic voltammograms at BDD MDA electrodes for the oxidation of (A) 1 mM ascorbic acid in 0.1 M Na2S04 and (B) 1 mM DOPAC in 0.1 M Na2S04> potential sweep rate 10 mV s O.

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