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1.
The preparation and study of electrochemical properties of a graphite screen-printed electrode (SPE) modified with the GO/Fe3O4@SiO2 (GO is graphene oxide) nanocomposites are described. The morphologies of the GO/Fe3O4@SiO2 nanocomposites were examined by scanning electron microscopy. The electrochemical oxidation of vitamin B6 (pyridoxine) on SPE modified with the GO/Fe3O4@SiO2 nanocomposite was investigated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. Under optimum conditions (pH 7.0), the vitamin B6 oxidation at the surface of the modified SPE occurs at a potential about 190 mV less positive than that at the unmodified SPE. A linear voltammetric response for vitamin B6 was obtained in the concentration range 1.0?10 6—9.0?10 4 mol L–1 with a detection limit of 5.2?10 7 mol L–1 using differential pulse voltammetry. The developed sensor was also successfully applied for determination of trace level of vitamin B6 in both the standard vitamin B6 sample and biological samples (urine).  相似文献   

2.
A novel carbon paste electrode modified with ZrO2 nanoparticles and an ionic liquid (n-hexyl-3- methylimidazolium hexafluorophosphate) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for simultaneous voltammetric oxidation of dopamine and uric acid is described. The electrode was also employed to study the electrochemical oxidation of dopamine and uric acid, using cyclic voltammetry, chronoamperometry and square wave voltammetry as diagnostic techniques. Square wave voltammetry exhibits linear dynamic range from 1.0 × 10?6 to 9.0 × 10?4 M for dopamine. Also, square wave voltammetry exhibits linear dynamic range from 9.0 × 10?6–1.0 × 10?3 M for uric acid. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of dopamine and uric acid into two well-defined voltammetric peaks. In the mixture containing dopamine and uric acid, the two compounds can be well separated from each other with potential difference of 155 mV, which is large enough to determine dopamine and uric acid individually and simultaneously. Finally, the modified electrode was used for determination of dopamine and uric acid in real samples.  相似文献   

3.
A highly sensitive high-performance liquid chromatographic method with fluorescence detection has been developed for determination of vitamin B1. Vitamin B1 was converted into a fluorescent compound by treatment with hydrogen peroxide–horseradish peroxidase and the derivative was subsequently analyzed by HPLC on a Waters Spherisorb ODS2 column (250 mm×4.6 mm ID, 5 μm) with 40:60 methanol–pH 8.5 acetate buffer solution as mobile phase and fluorescence detection at 440 nm (with excitation at 375 nm). The calibration graph was linear from 5.00×10−10 mol L−1 to 5.00×10−7 mol L−1 for vitamin B1 with a correlation coefficient of 0.9991 (n=9). The detection limit was 1.0×10−10 mol L−1. The method was successfully used for determination of vitamin B1 at pg mL−1 levels in microalgal fermentation media and seawater after solid-phase extraction. Recovery was from 89 to 110% and the relative standard deviation was in the range 1.1 to 4.3%.  相似文献   

4.
Simultaneous determination of the fat-soluble vitamins A and E and the water-soluble vitamins B1, B2 and B6 has been carried using a screening method from fluorescence contour graphs. These graphs show different colour zones in relation to the fluorescence intensity measured for the pair of excitation/emission wavelengths. The identification of the corresponding excitation/emission wavelength zones allows the detection of different vitamins in an aqueous medium regardless of the fat or water solubility of each vitamin, owing to the presence of a surfactant which forms micelles in water at the used concentration (over the critical micelle concentration). The micelles dissolve very water insoluble compounds, such as fat-soluble vitamins, inside the aggregates. This approach avoids the use of organic solvents in determining these vitamins and offers the possibility of analysing fat- and water-soluble vitamins simultaneously. The method has been validated in terms of detection limit, cut-off limit, sensitivity, number of false positives, number of false negatives and uncertainty range. The detection limit is about g L–1. The screening method was applied to different samples such as pharmaceuticals, juices and isotonic drinks.  相似文献   

5.
A procedure was developed for the gas-chromatographic determination of hydrocarbons in silicon tetrafluoride of natural and isotopically enriched compositions. For improving the efficiency of the chromatographic determination of impurities, it was proposed that the major compound be removed from the test sample with the subsequent cryofocusing of impurity hydrocarbons. The detection limits of C1-C4 hydrocarbons were 2 × 10?6?6 × 10?6 vol %.  相似文献   

6.
A method to determine vitamin B12 by measuring the chemiluminescence (CL) intensities using a flow injection (FI) system has been proposed. It is based on the catalytic effect of cobalt(II) in vitamin B12 on the CL reaction between luminol and hydrogen peroxide in a basic medium. The increment of the CL intensity is proportional to the concentration of vitamin B12 in the range 8.68–86.9 ng/mL (r 2 = 0.9984) with a detection limit (3σ) of 0.89 ng/mL. The CL response is obtained in 10 s at a flow rate of 3.0 mL/min with a relative standard deviation (RSD) of less than 2.5% (n = 6). The method has been successfully applied to the determination of vitamin B12 in pharmaceutical injections. The text was submitted by the authors in English.  相似文献   

7.
A new type of graphene-Co3O4 functionalized porphyrin was synthesized and used for selective and sensitive detection of methyl parathion (MP). Co3O4 nanoparticles were firstly modified onto graphene oxide sheets and the porphyrin/Co3O4/graphene nanocomposites were then synthesized by self-assembly decoration of anion porphyrin on Co3O4-modified graphene sheets by π–π stacking. By dexterously controlling the electrochemical reduction variables and optimizing the electrode preparation parameters, with the satisfactory conductivity, strong adsorption toward MP, the developed novel sensor fabricated with the as-synthesized nano-assembly for determination of MP shows some satisfactory properties such as a wide linear concentration range (from 4.0?×?10?7 M to 2.0?×?10?5 M), low detection limit (1.1?×?10?8 M), favorable repeatability, long-time storage stability, and satisfactory anti-interference ability. It also had high precision for the real sample analysis, which indicated the good perspective for field application.  相似文献   

8.
LiNi0.80Co0.15Al0.05O2 (NCA) is explored to be applied in a hybrid Li+/Na+ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO4 solution as the electrolyte. It is found that during electrochemical cycling both Na+ and Li+ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g?1 and 95% coulombic efficiency under 0.1 C (1 C?=?120 mA g?1) current rate between 1.5–4.1 V. It also shows excellent rate capability that reaches 92 mAh g?1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage.  相似文献   

9.
The electrochemical behavior of vitamin B2 at a glassy-carbon electrode is studied. Some physicochemical parameters of the electrode reaction (pK values for different forms of vitamin B2 and the number of electrons involved in the electrode process) are calculated. A rapid procedure is developed for the quantitative chemical determination of vitamin B2 in breast milk by differential voltammetry.  相似文献   

10.
A facile, rapid and ultra‐sensitive method for the determination of vitamin B12 (cyanocobalamin) at the sub‐nanomolar concentration range by using low‐cost, disposable graphite screen‐printed electrodes is described. The method is based on the cathodic preconcentration of square planar vitamin B12s, as occurred due to the electro reduction of Co(III) center in vitamin B12a to Co(I), at ?1.3 V versus Ag/AgCl/3 M KCl for 40 s. Then, an anodic square wave scan was applied and the height of the peak appeared at ca. ?0.73 V versus Ag/AgCl/3 M KCl, due to the oxidation of Co(I) to Co(II) in the adsorbed molecule, was related to the concentration of the vitamin B12 in the sample. EDTA was found to serve as a key‐component of the electrolyte by eliminating the background signal caused by metal cations impurities contained in the electrolyte (0.1 M phosphate buffer in 0.1 M KCl, pH 3). It also blocks trace metals contained in real samples, thus eliminating their interference effect. The method was optimized to various working parameters and under the selected conditions the calibration curve was linear over the range 1×10?10–8×10?9 mol L?1 vitamin B12 (R2=0.994), while the limit of detection for a signal‐to‐noise ratio of 3 (7×10?11 mol L?1 vitamin B12) is the lowest value of any reported in the literature for the electrochemical determination of vitamin B12. The sensors were successfully applied to the determination of vitamin B12 in pharmaceutical products.  相似文献   

11.
《Electroanalysis》2006,18(8):830-834
A facile method for the simultaneous measurement of tryptophan (Trp) and tyrosine (Tyr) was firstly exploited at unmodified boron‐doped diamond (BDD) electrode. The experimental results indicated that by using differential pulse voltammetry, the oxidative peaks of these two kinds of amino acids could be completely separated at BDD electrode. The peak separation of Trp and Tyr was developed to be 0.64 V when Na2PO4/NaOH buffer solution with the optimized pH 11.2 was employed. The detection limit of Trp was obtained to be 1×10?5 M, while that of Tyr was achieved to be 1×10?6 M. The present method was also evidenced to be available to the determination of real samples of amino acids.  相似文献   

12.
The kinetics of Ru[(NH3)6]3+ reduction in 1 M NaNO3 solution at Ag(210) and Ag(111) singlecrystal electrodes modified by n-decanthiol monolayer is studied by electrochemical impedance spectroscopy and cyclic voltammetry. By using these two methods, standard rate constants of the redox reaction involving Ru[(NH3)6]3+/2+ redox couple in the absence and in the presence of the n-decanthiol film were estimated. The equivalent circuit describing the experimental data in the presence of the self-assembled organic monolayer and in the absence of redox reaction is an electrical circuit comprising a large resistance (∼106 Ω) connected in parallel with a capacitance (∼10−8 F). Analysis of kinetic data and extrapolation of Tafel lines resulted in the determination of the rate constant at unmodified Ag-electrode, which is characteristic of very fast heterogeneous electron transfer. The calculated rate constants for n-decanthiol-modified silver singlecrystal faces (210) and (111) in 1 M NaNO3 solution (pH 6.3) equal 4.63 × 10−5 and 3.05 × 10−5 cm/s, respectively. The results are compared with the data at hand reported by different authors for gold electrodes in indifferent electrolyte solution in the absence and in the presence of self-assembled monolayer.  相似文献   

13.
Vitamin B1‐selective electrodes with PVC membrane were developed that contain ion associates of vitamin B1 with an inorganic anion, BiI4?, and an organic anion, brilliant yellow, as electrode‐active substances. The linearity ranges of the electrode function are 1.0×10?5–1.0×10?2 and 1.0×10?4–1.0×10?2 M, the electrode function slopes are 33.0±1.0 and 33.1±1.1 mV decade?1, the detection limits are 5.5×10?6 and 8.3×10?5 M for BiI4? and brilliant yellow respectively. The working range of pH is 5–12. The efficiency of the use of electrodes for the vitamin B1 content control in multivitamin pharmaceutical preparations was shown by direct potentiometry and potentiometric titration methods.  相似文献   

14.
The preparation of a carbon ceramic electrode modified with SnO2 (CCE/SnO2) using tin dibutyl diacetate as precursor was optimized by a 23 factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO2 provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO2, indicating that SnO2 when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10?5 to 6.97×10?4 mol L?1 with quantification and detection limits of 3.80×10?5 mol L?1 (14.07 mg L?1) and 1.13×10?5 mol L?1 (4.18 mg L?1), respectively.  相似文献   

15.
A polyoxometalate-nanocarbon composite, PMo11V@N-CNT, was prepared by a simple procedure which consisted of the immobilization of phosphovanadomolybdate (PMo11V) onto N-doped carbon nanotubes (N-CNT). The FTIR and XPS characterizations confirmed its successful synthesis. The cyclic voltammograms of glassy carbon electrode (GCE) modified with PMo11V and PMo11V@N-CNT showed four Mo-centred redox processes (MoVI/V) and a vanadium redox process (VV/IV). All were surface-confined redox processes. Additionally, PMo11V@N-CNT/GCE showed good stability and well-resolved redox peaks with high current intensities. The electrocatalytic sensing properties of PMo11V@N-CNT/GCE towards acetaminophen (AC) in the presence of tryptophan (TRP) were evaluated by square wave voltammetry. Under the conditions used, the peak current increased linearly with AC concentration in the presence of TRP, with a linear range from 1.5 × 10?6 to 3.9 × 10?4 mol dm?3 and a detection limit of 1.0 × 10?6 mol dm?3.  相似文献   

16.
A carbon paste electrode (CPE) modified with Fe3O4 nanoparticles (Fe3O4 NP) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (IL BMI.PF6) was employed for the electroanalytical determination of estrone (E1) by square-wave voltammetry (SWV). At the modified electrode, cyclic voltammograms of E1 in B–R buffer (pH 12.0) showed an adsorption-controlled irreversible oxidation peak at around +0.365 V. The anodic current increased by a factor of five times and the peak potential shifted 65 mV to less positive values compared with the unmodified CPE. Under optimized conditions, the calibration curve obtained showed two linear ranges: from 4.0 to 9.0 μmol L?1 and from 9.0 to 100.0 μmol L?1. The limits of detection (LOD) and quantification (LOQ) attained were 0.47 and 4.0 μmol L?1, respectively. The proposed modified electrode was applied to the determination of E1 in pork meat samples. Data provided by the proposed modified electrode were compared with data obtained by UV–vis spectroscopy. The outstanding performance of the electrochemical device indicates that Fe3O4 NP and the IL BMI.PF6 are promising materials for the preparation of chemically modified electrodes for the determination of E1.  相似文献   

17.
Solid solutions based on cesium monogallate CsGaO2 are synthesized in the Ga2O3-TiO2-Cs2O system. Their crystalline structure and also temperature and concentration conductivity dependences are studied. The cesium cation character of conductivity is confirmed. The most conducting samples contain an excess of cesium oxide and have the structure of high-temperature γ-modification of KAlO2. Their specific conductivity is (5.0–6.7) × 10?3 S cm?1 at 400 °C, (2.5–5.0) × 10?2 S cm?1 at 700°C at the activation energy of 33–35 kJ/mol?1.  相似文献   

18.
The electrochemical oxidation of vinylsulphone azo dye, Reactive Black 5 (RB5), at a glassy carbon electrode has been carried out in phosphate buffer solutions in the pH range 2.85?C11.79 employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). RB5 showed one well-defined oxidation peak at 0.560 V vs. Ag-AgCl using DPV. The oxidation process was shown to be irreversible over the pH range 2.85?C8.39 and was diffusion controlled. The linear relationship between the peak current height and RB5 concentrations allowed the differential pulse voltammetric determination of the dye over a wide concentration range, from 6.0 × 10?7 to 1.5 × 10?6 M with a detection limit of 4.0 × 10?7 M. The precision and recovery did not exceed 4.9 and 98.2%, respectively. A UV-Vis spectrophotometry method was also proposed for the determination of the RB5 in concentration range from 5.0 × 10?6 M to 1.0 × 10?5 M at ??max = 600 nm with limit of detection of 4.7 × 10?6 M and RSD of 1.8% for RB5 concentration of 1.0 × 10?5 M.  相似文献   

19.
We report the synthesis of NiCo2O4/reduced graphene oxide (NiCo2O4/rGO) hybrid hierarchical structures with unique nanonet and microsphere morphologies by organic polar solvent-assisted solvothermal method. The electrocatalytic oxygen evolution reaction (OER) activity of these materials is studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods in O2-saturated 0.1 M KOH solution. The NiCo2O4/rGO hybrid nanocomposite materials are found to be highly active electrocatalysts for OER at lower overpotentials. The nanonet and microsphere-like NiCo2O4/rGO catalysts require overpotentials of 0.450 and 0.530 V at a current density of 10 mA cm?2, and their corresponding Tafel slopes are 53 and 62 mV dec?1, which are much lower than values reported for non-precious electrocatalysts. Further, both NiCo2O4/rGO catalysts show good catalytic stability with current retention more than 92 % over long period of 15,000 s determined by chronoampirometry and at the end of 1000th cycle determined by linear sweep voltammetry. The enhanced OER activity of nanostructured NiCo2O4/rGO hybrid catalysts is attributed to synergistic interaction between rGO and NiCo2O4, which seems to be essential for maintaining the large contact area at the electrode-electrolyte interface, better mass, and charge transport and to minimize the aggregation of NiCo2O4 nanoparticles.  相似文献   

20.
Properties of CF x /Li and CF x /Na cells were examined while using galvanostatic charging/discharging, electrochemical impedance spectroscopy and scanning electron microscopy (SEM). The capacity during the first cycle was as high as ca. 1000 mAh g?1. Such an electrode is suitable for primary CF x /Li and CF x /Na batteries. SEM images of CF x cathode showed that during discharging it was transformed into amorphous carbon and LiF or NaF crystals (of diameter of ca. 5–20 μm). These systems (C?+?LiF or C?+?NaF) cannot be reversibly converted back into CF x /Li or CF x /Na, respectively. Exchange current densities are between 10?7 Acm?2 and 10?9 Acm?2 when working with LiPF6 and NaPF6 electrolytes (1.12?×?10?7 Acm?2 and 6.82?×?10?9 Acm?2, respectively). Those values are low and indicate that the charge transfer process may be the rate-determining step. Activation energies for the charge transfer process were 57 and 72 kJ mol?1 for CF x /LiPF6 and CF x /NaPF6 systems, respectively. Higher activation energy barrier for the CF/Na+?+?e??→?C?+?NaF reaction results in lower observed exchange current density in comparison to the system with lithium ions.  相似文献   

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