Large Excess Of Ascorbic Acid Research Articles

Differential Electroanalysis of Dopamine in the Presence of a Large Excess of Ascorbic Acid at a Nickel Oxide Nanoparticle-Modified Glassy Carbon Electrode

Electrochemical determination of dopamine (DA) in the presence of a large excess of ascorbic acid (AA) in their coexistence at a nickel oxide nanoparticle-modified preoxidized glassy carbon electrode (GCox/nano-NiOx) is achieved. The GCox/nano-NiOx electrode is prepared by electrodeposition of nickel nanoparticles (nano-Ni) onto an electrochemically activated glassy carbon (GC) electrode, and the thus prepared nano-Ni were subjected to electrochemical oxidation in alkaline medium for the formation of nickel oxide (NiOx). Modified electrodes were electrochemically and morphologically characterized. The effect of loading level of nickel was investigated by changing the number of potential cycles for the deposition of nano-Ni, i.e., 1, 2, 5, and 10 potential cycles, in the potential range from 0 to -1.0 V vs. SCE. Also, the experimental and instrumental parameters were optimized. Experimental results showed that the modified electrode differentiates well the oxidation peaks of DA and AA enabling the electrochemical determination of DA in the presence of a large excess of AA. Remarkably, it is found that the oxidation current of DA is 2 times larger than that of AA even the concentration of AA is about 5 times larger than that of DA. The LOD and LOQ of DA were calculated and were found to equal 0.69 and 2.3 mM, respectively. This offers the advantage of simple and selective detection of DA free of the interference of AA in real samples.

Prospective mechanistic on electron-transfer nature for reduction of permanganate ion by ascorbic acid in aqueous acidic solutions

A conventional spectrophotometer has been applied for investigating the kinetics of reduction of permanganate ion by ascorbic acid (vitamin C) in aqueous media. The oxidation process showed complexity kinetics. First- order dependences in each of the reactants and second-order overall kinetics has been observed. The decrease in the oxidation rates with increasing the [H+] indicated that the oxidation was of acid-inhibition nature. Kinetics and spectrophotometric evidences for formation of intermediate complexes through the oxidation process have been revealed. Formation of free-radical intervention was confirmed by the test of acrylonitrile reagent. Formation of either Mn3+ and/Mn4+ as the more reactive species through the progression of reaction were confirmed by the added Mn2+ and F− species. The naked-eyes observation indicated that the purple color of permanganate ion was firstly turned into rose color, which is rapidly disappeared to give a colorless solution. A black brownish of colloidal aggregate sol was formed by aging the colorless solution particularly in the presence of large excess of ascorbic acid over that of permanganate ion concentration, The analysis of the derivatives indicated the formation of dehydroscobic acid and manganese (0) nanoparticles as final oxidation products. An inner-sphere mechanism of two electron changes in a single step was suggested and discussed in terms of the evaluated activation parameters and kinetic observations.

Simultaneous Detection of Morphine and Codeine in the Presence of Ascorbic Acid and Uric Acid and in Human Plasma at Nafion Single-Walled Carbon Nanotube Thin-Film Electrode.

In clinical settings, the dosing and differential diagnosis of the poisoning of morphine (MO) and codeine (CO) is challenging due to interindividual variations in metabolism. However, direct electrochemical detection of these analytes from biological matrices is inherently challenging due to interference from large concentrations of anions, such as ascorbic acid (AA) and uric acid (UA), as well as fouling of the electrode by proteins. In this work, a disposable Nafion-coated single-walled carbon nanotube network (SWCNT) electrode was developed. We show facile electron transfer and efficient charge separation between the interfering anions and positively charged MO and CO, as well as significantly reduced matrix effect in human plasma. The Nafion coating alters the voltammetric response of MO and CO, enabling simultaneous detection. With this SWCNT/Nafion electrode, two linear ranges of 0.05–1 and 1–10 μM were found for MO and one linear range of 0.1–50 μM for CO. Moreover, the selective and simultaneous detection of MO and CO was achieved in large excess of AA and UA, as well as, for the first time, in unprocessed human plasma. The favorable properties of this electrode enabled measurements in plasma with only mild dilution and without the precipitation of proteins.

Magnetic Mixed Micelles Composed of a Non-Ionic Surfactant and Nitroxide Radicals Containing a D-Glucosamine Unit: Preparation, Stability, and Biomedical Application.

Metal-free magnetic mixed micelles (mean diameter: < 20 nm) were prepared by mixing the biocompatible non-ionic surfactant Tween 80 and the non-toxic, hydrophobic pyrrolidine-N-oxyl radicals bearing a d-glucosamine unit in pH 7.4 phosphate-buffered saline (PBS). The time-course stability and in vitro magnetic resonance imaging (MRI) contrast ability of the mixed micelles was found to depend on the length of the alkyl chain in the nitroxide radicals. It was also confirmed that the mixed micelles exhibited no toxicity in vivo and in vitro and high stability in the presence of a large excess of ascorbic acid. The in vivo MRI experiment revealed that one of these mixed micelles showed much higher contrast enhancement in the proton longitudinal relaxation time (T1) weighted images than other magnetic mixed micelles that we have reported previously. Thus, the magnetic mixed micelles presented here are expected to serve as a promising contrast agent for theranostic nanomedicines, such as MRI-visible targeted drug delivery carriers.

An electrochemical sensor based on graphene/poly(brilliant cresyl blue) nanocomposite for determination of epinephrine

A graphene modified with poly(brilliant cresyl blue) (PBCB) glassy carbon electrode was fabricated by a simple method of drop-casting and two-step-electropolymerization for facilitating electrocatalytic detection of epinephrine (EP). Surface characterization of PBCB/graphene/GCE was conducted by electrochemical impedance spectroscopy (EIS), whose results showed that the electron transfer process at PBCB/graphene is faster than at bare GCE, graphene/GCE and PBCB/GCE. And the scanning electron microscopy (SEM) image confirmed the graphene dispersion incorporated with PBCB on the GCE. A noticeable enhancement in the microscopic area of the electrode resulted in an appreciable increase of the peak current of EP oxidation (~9.4 times). The catalytic oxidation peak currents obtained from cyclic voltammetry (CV) increased linearly with EP concentrations in the range of 1.0×10−6 to 1.0×10−3mol/L with the limit of detection 2.4×10−7mol/L (S/N=3). Furthermore, the fabricated PBCB/graphene/GCE nanocomposite can determine EP in the presence of a large excess of ascorbic acid (AA) and uric acid (UA) by differential pulse voltammetry (DPV). The modified electrode can be used for the determination of EP in practical pharmaceutical formulation.

Simultaneous electroanalysis of norepinephrine, ascorbic acid and uric acid using poly(glutamic acid) modified carbon paste electrode

A sensitive, selective and reproducible electrochemical method was developed for the electroanalysis of norepinephrine (NE) using poly(glutamic acid) modified carbon paste electrode. The modified electrode shows excellent electrocatalytic activity towards the oxidation of NE in phosphate buffer solution (PBS) of pH 7.4 by cyclic voltammetric and differential pulse voltammetric techniques. The lower limit of detection of NE was found to be 0.43μM. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid (AA) and uric acid (UA). The separation of the oxidation peak potentials for NE–AA and NE–UA were about 0.262V and 0.122V, respectively. This peak differences were large enough to determine NE, AA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect NE in the presence of AA and UA.

Graphene-supported poly[iron (II) tetraphenylporphyrin] hybrid fabricated by a solvothermally assisted π–π assembly method and its application for the detection of dopamine

A novel composite consisting of poly[iron (II) tetraphenylporphyrin] (PFeTPP) and poly(sodium-p-styrenesulfonate) (PSS) modified graphene (Gr), denoted as PFeTPP/PSS-Gr, was obtained by a solvothermal method and used for the voltammetric determination of dopamine (DA). Compared with either pristine PFeTPP or PSS-Gr, the fabricated composite exhibits superior electrocatalytic activity towards the oxidation of DA. Its oxidation peak current shows a linear dependence over the DA concentration in the range from 0.1 to 40μM, with a detection limit of 5.73nM (S/N=3). Furthermore, the fabricated PFeTPP/PSS-Gr composite can detect DA in the presence of a large excess of ascorbic acid (AA) and uric acid (UA). Our proposed sensor conceivably represents a promising material for bioanalytical applications.

Voltammetric Resolution of Dopamine in Presence of Ascorbic Acid and Uric Acid at Poly (Brilliant Blue) Modified Carbon Paste Electrode

Poly (brilliant blue) modified carbon paste electrode was fabricated for the detection of dopamine in the presence of large excess of ascorbic acid and uric acid in phosphate buffer solution of pH 7.4. The redox peaks obtained at poly (brilliant blue) modified carbon paste electrode shows good electrocatalytic activity towards the oxidation of dopamine. From the study of scan rate variation the electrode process was found to be adsorption controlled. The limit of detection of dopamine was found to be 6.7 × 10-7 M. and the simultaneous study shows the good result with peak to peak separation between dopamine and other two analytes ascorbic acid and uric acid by both cyclic voltammetry and differential pulse voltammetric techniques

Novel sensitive electrochemical sensor for simultaneous determination of epinephrine and uric acid by using a nanocomposite of MWCNTs–chitosan and gold nanoparticles attached to thioglycolic acid

A promising electrochemical sensor for simultaneous determination of epinephrine (EP) and uric acid (UA) was fabricated by electrodeposition of Au-nanoparicles (AuNPs) on thioglycolic acid (TGA) film. TGA film was stabilized by covalent attachment to chitosan–MWCNTs composite on a glassy carbon electrode. The average size of AuNPs obtained by SEM was 110±5nm. AuNPs/TGA/CS–MWCNTs/GCE exhibited remarkable electrocatalytic activity towards the oxidation of epinephrine (EP) and uric acid (UA) in the presence of a large excess of ascorbic acid. Under the optimum experimental conditions, the detection limits of 60nM for EP and 32nM for UA were achieved by using amperometric method. The sensitivity of the method was 2.31μAμM−1 and 0.45μAμM−1 for EP and UA, respectively. The modified electrode was applied successfully to the simultaneous determination of EP and UA in human blood serum by DPV method. Good stability and durability in the determination of EP and UA were observed for the sensor.

Voltammetric determination of uric acid in the presence of ascorbic acid and dopamine using chitosan/ionic liquid composite electrode

A chitosan/ionic liquid composite electrode was prepared and used to determine uric acid (UA) in the presence of a large excess of ascorbic acid (AA) and dopamine (DA) by linear sweep voltammetry (LSV). The modified electrode shows large peak separations between DA, AA, and UA. Due to the existence of chitosan and ionic liquid in the composite, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of UA. Under optimal conditions, the peak current is linearly dependent on the UA concentration in the range of 5 × 10−7–2 × 10−4 M in the presence of 5 × 10−4 M AA and 5 × 10−5 M DA with a correlation coefficient of 0.9978, and the detection limit is 5 × 10−8 M at a signal-to-noise ratio of 3. With good sensitivity and stability, the constructed sensor was applied in the determination of UA in human serum samples and satisfactory results were obtained.

Highly Sensitive and Selective Determination of Dopamine in the Presence of Ascorbic Acid Using Gold Nanoparticles‐Decorated MoS2 Nanosheets Modified Electrode

AbstractHerein, a novel nanocomposite has been synthesized by molybdenum disulfide (MoS2) nanosheets and gold nanoparticles (AuNPs) via a microwave‐assisted hydrothermal method, which possesses the specific features of both MoS2 and AuNPs. The AuNPs@MoS2 nanocomposite modified electrode exhibits excellent electrocatalytic activity toward dopamine (DA). Its oxidation peak current shows a linear dependence over the DA concentration in the range from 0.1 to 200 µM, with a detection limit of 80 nM (S/N=3). More importantly, the AuNPs@MoS2‐based sensor can detect DA in the presence of a large excess of ascorbic acid. The AuNPs@MoS2‐based sensor shows good sensitivity, reproducibility and selectivity, suggesting that the AuNPs@MoS2 nanocomposite is a promising candidate in electrochemical sensing and other electrocatalytic applications.

Pretreated/Carbon paste electrode based voltammetric sensors for the detection of dopamine in presence of ascorbic acid and uric acid

A voltammetric resolution for the determination of dopamine using a Pretreated/Carbon paste electrode was developed. The Pretreated/Carbon paste electrode showed excellent electrocatalytic activity towards the oxidation of dopamine in phosphate buffer solution (pH 7.0). From the electrochemical studies of scan rate, the overall electrode process was diffusion and adsorption controlled. The pH effect suggested that equal number of protons and electrons were involved in the electrochemical detection of dopamine. Detection limit (LOD) was calculated in phosphate buffer solutions at pH 7.0 and the interference studies showed that the modified electrode exhibited excellent selectivity in the presence of large excess of ascorbic acid and uric acid. The separation of the oxidation peak potentials for dopamine–ascorbic acid and dopamine–uric acid was found to be 0.187V and 0.121V, respectively. These differences were large enough to determine dopamine, ascorbic acid and uric acid individually and simultaneously by using cyclic voltammetry and differential pulse voltammetric techniques.

Multi-walled carbon nanotube/poly(glycine) modified carbon paste electrode for the determination of dopamine in biological fluids and pharmaceuticals

A modified carbon paste electrode (CPE) for the selective detection of dopamine (DA) in presence of large excess of ascorbic acid (AA) and uric acid (UA) at physiological pH has been fabricated by bulk modification of CPE with multi-walled carbon nanotubes (MWCNTs) followed by electropolymerization of glycine (Gly). The surface morphology is compared using SEM images. The presence of nitrogen was confirmed by the energy dispersion X-ray spectroscopy (EDS) indicating the polymerization of Gly on the surface of the modified electrode. The impedance study indicates a better charge transfer kinetics for DA at CPE modified with MWCNT/polyglycine electrode. The presence of MWCNTs in carbon paste matrix triggers the extent of electropolymerization of Gly and imparts more selectivity towards DA by electrochemically not sensing AA below a concentration of 3.1×10−4M. Due to the exclusion of the signal for AA, the interference of AA in the determination of DA is totally ruled out by DPV method which is used for its detection at lower concentrations. Large peak separation, good sensitivity, reproducibility and stability allow this modified electrode to analyze DA individually and simultaneously along with AA and UA. Detection limit of DA was determined from differential pulse voltammetric (DPV) study and found to be 1.2×10−8M with a linear dynamic range of 5.0×10−7M to 4.0×10−5M. The practical analytical application of this electrode was demonstrated by measurement of DA content in dopamine hydrochloride injection and human blood serum.

Seed‐Mediated Synthesis of Single‐Crystal Gold Nanospheres with Controlled Diameters in the Range 5–30 nm and their Self‐Assembly upon Dilution

Single-crystal gold nanospheres with controlled diameters in the range 5-30 nm were synthesized by using a facile approach that was based on successive seed-mediated growth. The key to the success of this synthesis was the use of hexadecyltrimethylammonium chloride (CTAC) as a capping agent and a large excess of ascorbic acid as a reductant to ensure fast reduction and, thus, single crystallinity and a spherical shape of the resultant nanoparticles. The diameters of the gold nanospheres could be readily controlled by varying the amount of seeds that were introduced into the reaction system. The gold nanospheres could be produced with uniform diameters of up to 30 nm; thus, their localized surface plasmon resonance properties could be directly compared with the results that were obtained from theoretical calculations. Interestingly, we also found that these gold nanospheres self-assembled into dimers, larger aggregates, and wavy nanowires when they were collected by centrifugation, dispersed in deionized water, and then diluted to different volumes with deionized water.

Poly(m-phenylenediamine)–Prussian blue hybrid film formed by one-step electrochemical deposition for glucose biosensor

Hybrid film of poly(m-phenylenediamine) (PMPD) and Prussian blue (PB) has been formed on a glassy carbon (GC) electrode by one-step electrochemical deposition process for the construction of a highly sensitive and selective glucose biosensor. Due to the nanosized PB particles (ca. 40nm) in the PMPD–PB hybrid film, the modified GC electrode exhibited good electrochemical activity towards hydrogen peroxide reduction. The PMPD–PB modified electrode responded to hydrogen peroxide in the linear range from 0.0055mM to 1.0mM with a detection limit of 0.6μM (S/N=3). The PMPD–PB modified electrode showed good stability in neutral or weak alkaline solutions, and also strong anti-interference ability to other interfering electroactive species such as ascorbic acid and uric acid. Glucose biosensor was further constructed by immobilizing glucose oxidase on the PMPD–PB hybrid-modified electrode surface using gold nanoparticles and chitosan. The present biosensor responded linearly to glucose in the concentration range from 0.025mM to 0.65mM with a detection limit of 1.0μM (S/N=3). The response time was 10s and the sensitivity was 2.54mA/M. The present biosensor did not show any interference from large excess of ascorbic acid and uric acid. The constructed biosensor had good stability and reproducibility, thus could be applied to the glucose analysis of serum samples in practice.

Monodispersed Gold Nanoparticles Decorated Carbon Nanotubes as an Enhanced Sensing Platform for Nanomolar Detection of Tramadol

AbstractA promising composite‐modified glassy carbon electrode is fabricated by electrodeposition of mono‐dispersed gold nanoparticles onto carbon nanotubes (AuNPs/CNTs/GCE). The electroanalysis of Tramadol (TRA) was achieved by different electrochemical techniques. The effect of different parameters including pH, concentration and potential scan on the oxidation current signal of TRA was investigated. Large excess of ascorbic acid (AA) and uric acid (UA) with a maximum molar ratio of 1/1000 and 1/100, respectively, did not interfere with the response of TRA. The detection limit with high sensitivity is 68 nM. TRA was successfully determined in pharmaceutical dosage forms, without any pretreatment of the samples.

Selective determination of dopamine in presence of ascorbic acid and uric acid at hydroxy double salt/surfactant film modified carbon paste electrode

A sensitive and selective electrochemical method using a hydroxy double salt/surfactant film modified carbon paste electrode (HDS/SDS/CPE) was developed for the electrochemical determination of dopamine. The HDS/SDS/CPE shows an excellent electrocatalytic activity towards the oxidation of dopamine in 0.1M phosphate buffer solution (pH 7.4) and the detection limit of DA was 1×10−7M. The interference studies showed that the modified electrode exhibits an excellent selectivity towards dopamine (DA) in the presence of large excess of ascorbic acid (AA) and uric acid (UA). The separation of the oxidation peak potentials for DA–AA and DA–UA were about 187.8mV and 110.7mV respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect the dopamine in the presence of ascorbic acid and uric acid in physiological samples.

Electrochemical detection of dopamine using porphyrin-functionalized graphene

A new type of porphyrin-functionalized graphene was synthesized and used for highly selective and sensitive detection of dopamine (DA). The aromatic π–π stacking and electrostatic attraction between positively-charged dopamine and negatively-charged porphyrin-modified graphene can accelerate the electron transfer whereas weakening ascorbic acid (AA) and uric acid (UA) oxidation on the porphyrin-functionalized graphene-modified electrode. Differential pulse voltammetry was used for electrochemical detection, the separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA is about 188mV, 144mV and 332mV, which allows selectively determining DA. The detection limit of DA can be as low as 0.01μM. More importantly, the sensor we presented can detect DA in the presence of large excess of ascorbic acid and uric acid. With good sensitivity and selectivity, the present method was applied to the determination of DA in real hydrochloride injection sample, human urine and serum samples, respectively, and the results was satisfactory.

Simultaneous cyclic voltammetric determination of norepinephrine, ascorbic acid and uric acid using TX-100 modified carbon paste electrode

A sensitive and selective electrochemical method for the determination of norepinephrine (NE) using TX-100 modified carbon paste electrode was developed. The TX-100 modified carbon paste electrode shows excellent electrocatalytic activity towards the oxidation of NE in phosphate buffer solution (pH 7.0). The linear range of 0.5 × 10−4 to 2.0 × 10−4 M and detection limit of 5 × 10−6 M were observed at pH 7.0 phosphate buffer solution. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid (AA) and uric acid (UA). The separation of the oxidation peak potentials for NE–AA and NE–UA were about 0.16 V and 0.11 V, respectively. The differences were large enough to determine AA, NE and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect norepinephrine in the presence of ascorbic acid and uric acid in physiological samples.

Investigation of the electrochemical behavior of dopamine at electrodes modified with ferrocene-filled double-walled carbon nanotubes

Electrochemical properties of a new class of endohedral functionalized carbon nanomaterial, ferrocene-filled double-walled carbon nanotubes (Fc@DWNTs) have been investigated by preparing an Fc@DWNTs modified glassy carbon electrode (Fc@DWNTs/GCE). In an aqueous LiClO4 solution, one pair of redox peaks corresponding to the surface-confined Fc+/Fc couple was observed, suggesting that Fc molecules encapsulated inside DWNTs retain their electrochemical activity. Moreover, the Fc@DWNTs/GCE showed good stability because DWNTs could overcome the leaching of Fc from the modified electrode. Electrocatalytic oxidation of dopamine (DA) at the Fc@DWNTs modified electrodes was also obtained, indicating that encapsulated Fc molecules can serve as good electron-transfer mediators. In addition, due to the peculiar structure of Fc@DWNTs, direct electroreduction of oxidation product of DA was also observed. An electrochemical sensor for DA has been constructed based on Fc@DWNTs and a kind of cation exchange membrane, Nafion, which played a key role in the selectivity of the sensor. Amperometric measurements were conducted in the presence of a large excess of ascorbic acid (AA). The limit of detection was found to be 0.3μM based on S/N of 3.