Determination Of Ascorbic Acid In Vitamin Research Articles

Dual signal AA detection based on fluorescence and local surface plasmon resonance absorption technology

The core/shell Au@MnO2 nanoparticles (Au@MnO2 NPs) were prepared and characterized by UV–vis spectrum, transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). It was found that MnO2 in the shell of Au@MnO2 NPs could oxidize thiamine (VB1) into blue fluorescent thiochrome (TC). The reduction of MnO2 in the shell layer could lead to a decrease of Au@MnO2 NPs size along with a blue shift of the localized surface plasmon resonance (LSPR) peak. Once ascorbic acid (AA) was introduced, MnO2 in the shell was rapidly reduced to Mn2+ ions. Accordingly, the oxidation of VB1 was inhibited and the fluorescence of TC was weakened. Based on these phenomena, we have established a dual signal method for AA determination with the help of UV–vis and fluorescence spectrophotometer. Under the optimum conditions, the LSPR absorption peak shift (Δλ) of Au@MnO2 NPs and the decrease in fluorescence of TC correlated well with AA concentration ranging from 0.75 to 17.5 μM. The detection limits of LSPR absorption assay and fluorescence assay were 0.18 and 0.47 μM, respectively. More importantly, this dual-signal detection method has been used for the determination of AA in vitamin C tablets with high accuracy and precision, indicating its promising potential applications.

Molecularly imprinted electrochemical sensor for ascorbic acid determination based on MXene modified electrode

Molecularly imprinted electrochemical sensor for ascorbic acid (AA) detection was prepared based on MXene modified glassy carbon electrode (MIPs/MXene/GCE). MXene with layered structure was synthesized by chemical etching method and the o-phenylenediamine (o-PD) polymer was electrochemically polymerized onto MXene modified electrode surface. With the binding of AA molecules onto electrode, the current response of the sensor was decreased. Under the optimized experimental conditions, the current response change of the sensor was in linear with the concentration of AA in the range from 0.5 μM to 10 μM with detection limit of 0.27 μM. The sensor has good selectivity, which was applied to the determination of AA in vitamin C tablets.

A composite consisting of microporous carbon and cobalt(III) oxide and prepared from zeolitic imidazolate framework-67 for voltammetric determination of ascorbic acid.

A nanoporous carbon/cobalt oxide (NPC/Co3O4) composite was synthesized from a single-precursor (zeolitic imidazolate framework-67). Transmission electron microscopy showed that the Co3O4 nanoparticles with an average particle size of 10nm (±2nm) were well dispersed in the NPC matrix. However, in a few places, Co3O4 nanoparticles were aggregated. The composite shows outstanding performance in terms of electrooxidation of ascorbic acid (AA) in phosphate buffer of pH7.0. The differential pulse voltammetric response of the composite electrode (at 0.12V vs. SCE) is linear in the 2-240μM AA concentration range, with a 20nM detection limit. The electrode exhibits high sensitivity (0.13μA·μM·cm-2), reliable reproducibility, and good selectivity. The method, when applied to the direct determination of AA in vitamin C tablets, gave recoveries between 98.0and102.0%. Graphical abstract A nanoporous carbon composite decorated with Co2O3 nanoparticles was prepared from a single precursor (the zeolitic imidazolate framework-67). It shows outstanding performance in terms of electrooxidation of ascorbic acid with high sensitivity (0.13μA·μM·cm-2), reliable reproducibility, and good selectivity.

Multivariate Calibration Applied to the Simultaneous Spectrophotometric Determination of Ascorbic Acid, Tyrosine and Epinephrine in Pharmaceutical Formulation and Biological Fluids

Background: Epinephrine (EP), ascorbic acid (AA) and tyrosine (TY) usually coexist together in human blood and are considered as important molecules for physiological processes in human metabolism. Thus, to determine these compounds in biological fluids, we need to develop sensitive, simple and rapid methods. Method: The simultaneous spectrophotometric determination of AA, EP and TY, at pH=7.0 using multivariate calibration techniques such as principal component regression (PCR), partial least squares (PLS) and their first derivative methods have been carried out. Results: Satisfactory results were achieved using first derivative-partial least squares. After optimization of all variables, the linear ranges for AA, EP and TY were 0.8-35.0, 1.0-72.01 and 1.0-145.0 µgmL-1, respectively. The detection limits for AA, EP and TY obtained 0.1, 0.35 and 0.28 µgmL-1, respectively. Principal component (NPC) for AA, EP and TY were 2, 3 and 3. Prediction error sum of squares (PRESS) for AA, EP and TY were 2.37, 0.91 and 2.57, respectively. The root mean square errors of Prediction (RMSEP) for AA, EP and TY were 0.35, 0.16 and 0.60 respectively. Conclusion: Good agreement between prediction and actual concentrations clearly indicates the utilization of this procedure for the simultaneous determination of AA, EP and TY in serum, plasma and urine samples and also for the determination of AA in vitamin c tablet and EP in epinephrine injection. Keywords: UV–vis spectrophotometry, multivariate calibration, simultaneous determination, ascorbic acid, epinephrine, tyrosine.

Electrocatalytic simultaneous determination of ascorbic acid, uric acid and l–Cysteine in real samples using quercetin silver nanoparticles–graphene nanosheets modified glassy carbon electrode

By immobilizing of quercetin at the surface of a glassy carbon electrode modified with silver nanoparticles and graphene nanosheets (Q–AgNPs–GNs–GCE) a new sensor has been fabricated. The cyclic voltammogram of Q–AgNPs–GNs–GCE shows a stable redox couple with surface confined characteristics. Q–AgNPs–GNs–GCE demonstrated a high catalytic activity for l–Cysteine (l–Cys) oxidation. Results indicated that l–Cys peak potential at Q–AgNPs–GNs–GCE shifted to less positive values compared to GNs–GCE or AgNPs–GCE. Also, the kinetic parameters such as the electron transfer coefficient,, and the heterogeneous electron transfer rate constant, k′, for the oxidation of l–Cys at the Q–AgNPs–GNs–GCE surface were estimated. In differential pulse voltammetric determination, the detection limit of l–Cys was obtained 0.28μM, and the calibration plots were linear within two ranges of 0.9–12.4μM and 12.4–538.5μM of l–Cys. Also, the proposed modified electrode is used for the simultaneous determinations of ascorbic acid (AA), uric acid (UA), and l–Cys. Finally, this study has demonstrated the practical analytical utility of the sensor for determination of AA in vitamin C tablet, l–Cys in a milk sample and UA in a human urine sample.

Layer-by-layer assembly of poly(p-aminobenzene sulfonic acid)/quaternary amine functionalized carbon nanotube/p-aminobenzene sulfonic acid composite film on glassy carbon electrode for the determination of ascorbic acid

An excellent p-aminobenzene sulfonic acid (p-ABSA) monolayer film was fabricated on glassy carbon electrode (GCE) by situ electrochemical oxidation. Then a novel kind of homogeneous quaternary amine-functionalized carbon nanotube (q-CNT) film was adsorbed onto p-ABSA/GCE through electrostatic interaction to produce q-CNT/p-ABSA/GCE. Finally an electropolymerized poly(p-ABSA) film was formed on q-CNT/p-ABSA/GCE. The electrostatic layer-by-layer assembly process of the modified electrode poly(p-ABSA)/q-CNT/p-ABSA/GCE was well characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The modified electrode exhibited excellent electrocatalytic activity toward ascorbic acid (AA) oxidation at a low potential of +0.02V in pH7.0 PBS. Amperometric experiments were performed for the sensitive determination of AA. Linear responses in two concentration ranges of 0.002–0.06 and 0.1–3.20mM were obtained with the detection limit of 0.5μM (S/N=3). The electrostatic interaction of the positively charged q-CNTs with the monolayer p-ABSA film and the poly(p-ABSA) film promoted to form a stable poly(p-ABSA)/q-CNT/p-ABSA composite film on GCE. So the poly(p-ABSA)/q-CNT/p-ABSA/GCE showed good reproducibility and stability, and was successfully employed for the determination of AA in vitamin C tablet and human urine real samples with satisfactory results.

Electrochemical studies of ascorbic acid, dopamine, and uric acid at adl-norvaline-deposited glassy carbon electrode

The electrochemical behavior of ascorbic acid (AA), dopamine (DA), and uric acid (UA) on a dl-norvaline-modified glassy carbon electrode (GCE) was studied by cyclic voltammetry. The bare GCE failed to distinguish the oxidation peaks of AA, DA, and UA in phosphate-buffered solution (pH 5.0), while the dl-norvaline-modified GCE could separate them efficiently. In differential pulse voltammetric (DPV) measurements, the modified electrode resolved the overlapped voltammetric responses of AA, DA, and UA into three well-defined voltammetric peaks. Under optimum conditions, the anodic peak currents of DPV for AA, DA, and UA were proportional to the concentration in the range of 20–400, 1–40, and 15–180 μmol/L, respectively, with a correlation coefficient (r) of around 0.998. The detection limits were 5, 0.3, and 10 μmol/L (S/N = 3) for AA, DA, and UA, respectively. Satisfactory results were achieved for the determination of AA in vitamin C tablets, DA in a dopamine ampoule sample, and UA in human blood serum samples.

Electroanalysis of ascorbic acid using poly(bromocresol purple) film modified glassy carbon electrode

We report a simple method for determination of ascorbic acid (AA) by using a glassy carbon electrode (GCE) modified with poly(bromocresol purple) (poly(BCP)/GCE). Compared with a bare GCE, the poly(BCP) film exhibited the obvious electrocatalytic effect towards ascorbic acid oxidation, which reduced the oxidation overpotential about 240mV with obviously increased current response. Under the optimized conditions, the catalytic current increased linearly with the concentration of AA in the range of 2.0×10−5–7.0×10−4M with the detection limit of 6.5×10−6M (S/N=3) in 0.1M phosphate buffer solution (pH 6.5). The interferences from different species and the repeatability of the poly(BCP)/GCE for the determination of AA were also investigated. The proposed method has been successfully applied to the determination of AA in vitamin C injection and tablet with satisfactory results.

An electrochemical ascorbic acid sensor based on palladium nanoparticles supported on graphene oxide

In this study, an electrochemical ascorbic acid (AA) sensor was constructed based on a glassy carbon electrode modified with palladium nanoparticles supported on graphene oxide (PdNPs-GO). PdNPs with a mean diameter of 2.6nm were homogeneously deposited on GO sheets by the redox reaction between PdCl42− and GO. Cyclic voltammetry and amperometric methods were used to evaluate the electrocatalytic activity towards the oxidation of AA in neutral media. Compared to a bare GC or a Pd electrode, the anodic peak potential of AA (0.006V) at PdNPs-GO modified electrode was shifted negatively, and the large anodic peak potential separation (0.172V) of AA and dopamine (DA), which could contribute to the synergistic effect of GO and PdNPs, was investigated. A further amperometric experiment proved that the proposed sensor was capable of sensitive and selective sensing of AA even in the presence of DA and uric acid. The modified electrode exhibited a rapid response to AA within 5s and the amperometric signal showed a good linear correlation to AA concentration in a broad range from 20μM to 2.28mM with a correlation coefficient of R=0.9991. Moreover, the proposed sensor was applied to the determination of AA in vitamin C tablet samples. The satisfactory results obtained indicated that the proposed sensor was promising for the development of novel electrochemical sensing for AA determination.

Electroless deposition of bis(4'-(4-Pyridyl)-2,2':6',2''-terpyridine)iron(II) thiocyanate complex onto carbon nanotubes modified glassy carbon electrode: application to simultaneous determination of ascorbic acid, dopamine and uric acid

A glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) and bis(pyterpy)iron(II) thiocyanate complex (pyterpy = 4'-(4-pyridyl)-2,2':6',2''-terpyridine) was investigated by voltammetric methods in acetate buffer solution (pH 5). Performances of the iron(II)-complex/MWNTs modified electrode were evaluated with differential pulse voltammetry and scanning electron microscopy (SEM). The modified glassy carbon electrode shows an excellent electrochemical response for ascorbic acid (AA), dopamine (DA) and uric acid (UA). The differential pulse voltammetry oxidation peaks for AA and DA, DA and UA, AA and UA are separated by 210, 136 and 346 mV, respectively. This separation permits the simultaneous determination of AA, DA and UA. The anodic peak currents of AA, DA and UA increase linearly with concentration in the range of 1.10×10-5-1.50×10-3 mol L-1, 9.0×10-7-1.20×10-3 mol L-1 and 2.00×10-6-1.50×10-3 mol L-1, respectively, with a correlation coefficient (r) always higher than 0.998. In addition, the modified electrode also shows good sensitivity and stability. Satisfactory results were achieved for the determination of AA in vitamin C tablets, DA in dopamine injection solution and UA in human blood serum samples

Fluorimetric Determination of Ascorbic Acid in Vitamin C Tablets Using Methylene Blue

In this study, a simple and sensitive fluorimetric method was described for the determination of Ascorbic Acid (AA). The procedure is based on the reaction between AA and Methylene Blue (MB). The fluorescence intensity of MB was measured at excitation and emission of 664 and 682 nm, respectively. MB concentration was decreased as a function of decreasing fluorescence intensity due to forming colorless form of MB (Leuco-MB) in the reaction between AA and MB. A linear relationship was obtained between the decreasing fluorescence intensity and the concentration of AA in the range of 3.0 x 10(-7)-6.0 x 10(-6) mol.l(-1). The detection limit was 2.5 x 10(-7) mol.l(-1). The proposed method was applied successfully for the determination of AA in Vitamin C tablets.