Electrochemical Responses Of Ascorbic Acid Research Articles

Co<SUB align="right">3O<SUB align="right">4/CuO composite nanopowder/sodium dodecyl sulphate modified carbon paste electrode based voltammetric sensors for detection of dopamine

The Co3O4/CuO composite nanopowder (NP) modified carbon paste electrode (MCPE) was prepared and immobilised by sodium dodecyl sulphate (SDS). The electrochemical performance of dopamine (DA) in 0.2 M phosphate buffer solution (PBS) of pH 7.4 at Co3O4/CuO NP MCPE immobilised with SDS (Co3O4/CuO/SDS MCPE) was investigated by cyclic voltammetric technique as well as compared with bare carbon paste electrode (BCPE) and SDS immobilised bare CPE (CPE/SDS). In addition the electrochemical responses of ascorbic acid (AA) and uric acid (UA) were tested separately and simultaneously. The effect of concentration, quantity and immobilisation time of SDS on the Co3O4/CuO NP MCPE for the detection of dopamine was examined and optimum condition was attained for further electrochemical studies. The effect of pH on the oxidation of DA at Co3O4/CuO/SDS MCPE was studied by using different pH of PBS. The obtained slope 0.0498 V/pH from the graph of pH vs. anodic peak potential shows the equal number of protons and electrons are involved in the electrochemical reaction. From the effect of scan rate studies, the slope obtained from the graph of log scan rate (ν) vs. the log of anodic peak current (Ipa) shows the adsorption controlled electrode process. The heterogeneous rate constant increases as increase in the scan rate. In the study of DA concentration variation, the limit of detection (LOD) was found to be 0.6 µM and was contrast with other reported modified electrodes, as well as revealed lower LOD value compare to most of other modified electrodes. In simultaneous determination of DA, AA and UA, the Co3O4/CuO/SDS MCPE shown good separation along with increase in the Ipa compared to BCPE, Co3O4/CuO NP MCPE and CPE/SDS. The Co3O4/CuO/SDS MCPE was effectively tested in DA injection as a real sample analysis and was found to be good percentage recovery values.

Electrochemical determination of ascorbic acid using Cu sulfide modified glassy carbon electrode

The electrochemical responses of ascorbic acid at the Cu-sulfide modified glassy carbon electrode have been analyzed by adjusting the scan rate, ascorbic acid concentration and species of the electrolytes. Two anodic cyclic voltammogram peaks (cvp1, cvp2) are located at +0.56 V and +0.33 V, and two cathodic cyclic voltammogram peaks (cvp1′, cvp2′) are located at +0.10 V and–0.40 V, respectively. The intensities of the cyclic voltammogram peaks increase linearly with the increase of the ascorbic acid concentration in a range of 0.0005–2 mM and scan rate ranging from 25 to 200 mV s–1. A Cu-sulfide modified glassy carbon electrode shows good determination ability for ascorbic acid in neutral solutions with the detection limit of 0.18 μM and 0.12 μM for cvp1 and cvp2, respectively, at a signal-to-noise ratio of 3. Cu sulfide modified glassy carbon electrode shows good reproducibility and stability.

Cu(II) complex /multiwall carbon nanotube modified electrode for the determination of ascorbic acid

A sensitive and selective method for the determination of ascorbic acid (AA) using [Cu(phen)2]2+/multiwalled carbon nanotubes modified glassy carbon electrode was developed. Electrochemical behavior and surface characteristics of the modified electrode were studied using scanning electrode microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The experimental results showed that the modified electrode enhanced the electrochemical response of AA and exhibited good analytical performance for AA determination from 10 to 1 042 μmol/L with a low detection limit of 9.67μmol/L (S/N=3). The modified electrode was also applied to the determination of AA in the Vitamin tablets and showed good recovery.

Comparison of electrochemical property between multiwalled carbon nanotubes and porous graphitized carbon monolith modified glassy carbon electrode for the simultaneous determination of ascorbic acid and uric acid

In this work, glassy carbon electrode (GCE) was modified with porous graphitized carbon monolith (CM) as a new nanomaterials and multi-walled carbon nanotubes (MWCNTs) for simultaneous determination of ascorbic acid (AA) and uric acid (UA). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed for the surface analysis of the modified electrodes. In this simultaneous detection, the electrochemical response of AA and UA on MWCNTs/GCE exhibited broad anodic peaks and were resolved into separated CV peaks at +45mV and +254mV, respectively. In comparison, two well resolved peaks of CM/GCE were obtained at -39mV and +233mV with flat base-lines for oxidation of AA and UA, respectively. Under the optimum conditions, the performance of porous graphitized carbon monolith were superior to MWCNTs modified glassy carbon electrode. For CM/GCE, the oxidation peak current was linearly dependent on AA and UA concentration in the range 0.195–4.04mM and 0.094–1.90mM, with the correlation coefficients (R2) greater than 0.997. Detection limits (S/N=3) were found 0.39μM and 0.15μM for AA and UA, respectively. The recoveries of the AA and UA from spiked human serum were 76.0–94.2%. In addition, the CM/GCE showed high sensitivity, good reproducibility and long-time stability at least 1month without significant loss of electrochemical signal.

Poly(pyrocatechol-3,5-disodiumsulfonate)/Multi-Walled Carbon Nanotubes Composite for Simultaneous Determination of Dopamine, Ascorbic Acid and Uric Acid

A novel poly(pyrocatechol-3,5-disodiumsulfonate)/multi-walled carbon nanotubes (PPD/MWCNT) composite film modified glassy carbon electrode (GCE) was fabricated and successfully used to simultaneously determine ascorbic acid (AA), dopamine (DA) and uric acid (UA). Owing to the synergistic effects of PPD and MWCNTs, the electrochemical responses of AA, DA and UA at PPD/MWCNTs/GCE were clearly superior to those at bare GCE. Additionally, the PPD/MWCNTs composite film could reduce the potential overlap of AA, DA and UA so as to favor simultaneous determination of the three substances. Under the optimum conditions, the linear calibration curves of AA, DA and UA were obtained by differential pulse voltammetry in the range of 10-1000, 1-100 and 4-1200 microM, and the detection limits were 5, 0.5 and 0.5 microM (S/N = 3) respectively. The results showed PPD/MWCNTs/GCE possessed good reproducibility and stability, and it could be applied to determine UA in human urine with satisfying recovery by standard addition method.

Electrochemical Behaviors of Ascorbic Acid at CuGeO3/Polyaniline Nanowire Modified Glassy Carbon Electrode

The electrochemical responses of ascorbic acid have been investigated by cyclic voltammetry on the CuGeO3/20wt% polyaniline nanowire modified glassy carbon electrode at room temperature. The results show that the modified electrode exhibits good analytical performance for the electrochemical detection of ascorbic acid in neutral solution. The intensities of the anodic cyclic voltammogram (CV) peaks increase linearly with the increase of the ascorbic acid concentration from 0.001 to 2 mM and scan rate from 25 to 200 mVs−1. CuGeO3/20wt% polyaniline nanowire modified glassy carbon electrode exhibits good reproducibility, stability, low detection limit of 0.61 μM and 0.26 μM for cvp1 and cvp2, respectively, which is better than those at other modified electrodes.

Fabrication of poly(orthanilic acid)–multiwalled carbon nanotubes composite film-modified glassy carbon electrode and its use for the simultaneous determination of uric acid and dopamine in the presence of ascorbic acid

A multiwalled carbon nanotubes (MWNT) modified glassy carbon electrode (GCE) coated with poly(orthanilic acid) (PABS) film (PABS–MWNT/GCE) has been fabricated and used for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA) by differential pulse voltammetry (DPV). Scanning electron microscopy, Fourier transform infrared spectra, and electrochemical techniques have been used to characterize the surface morphology of the PABS–MWNT composite film and the polymerization of ABS on electrode surface. In comparison with the bare GCE and the MWNT-modified GCE, the PABS–MWNT composite film-modified GCE, which combines the advantages of MWNT and the self-doped PABS, exhibits good selectivity and sensitivity for the simultaneous and selective determination of UA and DA in the presence of AA. Due to the different electrochemical responses of AA, DA, and UA, PABS–MWNT/GCE can resolve the overlapped oxidation peak of DA and UA into two well-defined voltammetric peaks with enhanced current responses using both cyclic voltammetry (CV) and DPV. The peak potential separations between DA and UA are 170 mV using CV and 160 mV using DPV, respectively, which are large enough for the selective and simultaneous determination of these species. In the presence of 0.5 mM AA, the DPV peak currents are linearly dependent on the concentration of UA and DA in the range of 6–55 and 9–48 μM with correlation coefficients of 0.997 and 0.993, respectively. The detection limits (S/N = 3) for detecting UA and DA are 0.44 and 0.21 μM, respectively. The PABS–MWNT/GCE shows good reproducibility and stability and has been used for the simultaneous determination of DA and UA in the presence of AA in samples with satisfactory results.

Electrochemical Characterization of Polymerized Cresol Red Film Modified Glassy Carbon Electrode and Separation of Electrocatalytic Responses for Ascorbic Acid and Dopamine Oxidation

A cresol red modified glassy carbon electrode was prepared using an electrochemical method. The cyclic voltammograms of the modified electrode indicate the presence of a couple of well-defined redox peaks, and the formal potential shifts in the negative direction with increasing solution pH. The modified electrode exhibits high electrocatalytic activity toward ascorbic acid oxidation, with an overpotential of 300 mV less than that of bare glassy carbon electrodes, and drastic enhancement of the anodic currents. The calibration graph obtained by linear sweep voltammetry for ascorbic acid is linear in the range of 50∼500 µM. The electrode markedly enhances the current response of dopamine and can separate the electrochemical responses of ascorbic acid and dopamine. The separation between the anodic peak potentials of ascorbic acid and dopamine is 190 mV by cyclic voltammetry. The linear sweep voltammetric peak currents for dopamine in the presence of 2 mM ascorbic acid vary linearly with a concentration of between 10 and 100 µM.

Electrocatalytic Oxidation of Ascorbic Acid at a Reduced C60-[dimethyl-(β-cyclodextrin)]2 and Nafion Chemically Modified Electrode

A C60-[dimethyl-(β-cyclodextrin)]2 and Nafion chemically modified electrode (CME) has been prepared by solution cast on a gold electrode. The CME can be electroreduced irreversibly in KOH aqueous solution. XPS and SEM were used to characterize the CME and the reduced CME. The reduced CME shows high electrocatalytic activity toward ascorbic acid oxidation, with an overpotential ca. 350 mV less than that of the bare gold electrode. The reduced CME can also separate the electrochemical responses of ascorbic acid and dopamine.

Electrochemical Characterization of Pyrocatechol Sulfonephthalein-Modified Glassy Carbon Electrode and Separation of Electrocatalytic Responses for Ascorbic Acid and Dopamine Oxidation

A pyrocatechol sulfonephthalein- (PS-) modified glassy carbon (PS/GC) electrode has been prepared by adsorption of PS on a glassy carbon electrode surface. Cyclic voltammograms of the PS/GC electrode indicate the presence of a couple of well-defined redox peaks, and the formal potential shifts in the negative direction with increasing solution pH. The relation between formal potential,E0′, and solution pH can be fit to the equationE0′(mV) = −51.4 pH + 538.7. The PS/GC electrode shows high electrocatalytic activity toward ascorbic acid oxidation, with an overpotential ca. 380 mV less than that of the bare electrode and a drastic enhancement of the anodic currents. The electrocatalytic reaction rate constant (k), which was decreased with increasing concentration of H2A, was determined using rotating disk electrode measurements. The values ofkwas also affected by the solution pH. The electrode can also separate the electrochemical responses of ascorbic acid and dopamine. The separation between the anodic peak potentials of ascorbic acid and dopamine is more than 50 mV by the differential pulse voltammetry.