Sodium sulfite/sulfur dioxide reacts with iron(III) in acidic range (pH 2–3.5) to form iron(II) which is complexed with 1,10-phenanthroline to form a stable orange-red complex with maximum absorption at 510 nm. Beer's Law is obeyed over the concentration range of 0.5–10 ppm of sulfur dioxide. 相似文献
A chemically modified graphite electrode was prepared by using a dual film of [Os(bpy)2(PVP)10Cl]Cl polymer and Nafion. The modified electrode showed excellent electrocatalytical activity for the oxidation of norepinephrine (NE) and an ability to eliminate efficiently the interference of ascorbic acid and other anions. The catalytic peak currents obtained from the cyclic voltammograms increased linearly with increasing concentration of NE. A log-log plot of catalytic current versus NE concentration showed a dual-linear relationship in the ranges 1.8 x 10(-8)-4.4 x 10(-6) M and 4.4 x 10(-6)-2.9 x 10(-4) M with correlation coefficients of 0.990 and 0.999, respectively. The detection limit was about 18 nM (3 delta). At a potential of +500 mV the chronoamperometric response showed a linear relationship between the steady state current and NE concentration in the range 1.3-130 microM. With a further increase in NE concentration a Michaelis-Menten-shaped response was observed. The apparent Michaelis-Menten constant and the maximum current were 1.7 mM and 86 microA, respectively. The modified electrode showed excellent reproducibility, sensitivity and stability for the determination of NE at trace levels. 相似文献
An amperometric method for the rapid detection of Escherichia coli (E. coli) by flow injection analysis (FIA) using an IrO2–Pd chemically modified electrode (CME) was developed in this paper. The method is based on a good marker β-d-galactosidase which was found in E. coli strains. β-d-galactosidase was produced by the induction of isopropyl β-d-thiogalactopyranoside (IPTG) and released from E. coli cells through the permeabilization of both polymyxin B nonapeptide and lysozyme to E. coli cells wall. The released β-d-galactosidase could catalyze the hydrolysis of the substrate p-aminophenyl β-d-galactopyranoside (PAPG) in the culture medium to produce 4-aminophenol which was proportional to the concentration of E. coli. Hence, E. coli could be detected by the determination of 4-aminophenol. An IrO2–Pd CME, which showed high sensitivity in determination of 4-aminophenol, was prepared as the electro-detector in FIA. The amplified response current of 4-aminophenol obtained at the IrO2–Pd CME was linear with the concentration of E. coli ranging from 2.0 × 102 to 1.0 × 106 cfu/mL, the detection limit of this method to E. coli was 150 cfu/mL and the complete assay could be performed in 3 h. 相似文献
Nickel aquapentacyanoferrate (NAPCF), a novel transition metal complex has been prepared and its ability to act as an electrocatalyst for BHA oxidation has been demonstrated. The cyclic voltammetric behaviour of the NAPCF modified electrode prepared by mechanical immobilization on the graphite electrode was well defined. A pair of redox peaks corresponding to the electrochemical behaviour of the NAPCF was observed at 0.35 V and 0.31 V, corresponding to the anodic and cathodic peaks respectively, with a formal potential of 0.33 V. The NAPCF modified electrode favoured electrocatalytic oxidation of BHA to occur at a greatly minimized overpotential of 0.48 V. Experiments were performed to characterize the electrode as an amperometric sensor for the determination of BHA. The anodic peak current was linearly related to BHA concentration in the range of 6.24x10(-7) M to 2.19x10(-4) M with a detection limit of 2.49x10(-7) M and a correlation coefficient of 0.9979. Amperometry in stirred solution exhibited quick and sensitive response to BHA, showing the possible application of the modified electrode in flow system analysis. The modified electrode retained its initial response for more than 2 months when stored in supporting electrolyte, owing to the chemical and mechanical stability of the NAPCF mediator. This modified electrode was also quite effective in the determination of BHA in commercial samples. 相似文献
Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H2O2) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM−1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.
Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H2O2) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM?1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.
Figure
A TiO2 nanorod film was directly grown on Ti substrate by a hydrothermal route, and was further employed for a supporting matrix to immobilize horseradish peroxidase as a biosensor electrode. The as-prepared hydrogen peroxide biosensor based on Nafion/HRP/TNR/Ti electrode exhibited fast response and excellent electrocatalytic activity toward H2O2, i.e., a high sensitivity (416.9 μA mM?1), a wide linear range (2.5?×?10?8 to 4.6?×?10?4 M) with a low detection limit (0.012 μM) and a small apparent Michaelis-Menten constant (33.6 μM). 相似文献
A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0×10–9–2.0×10–5 mol L–1. The detection limit was 1.0×10–9 mol L–1 (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC–ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0×10–9 mol L–1. Application of the method for determination of parathion in rice was satisfactory. 相似文献
The diffusion of sulfur dioxide into partially iodine-doped poly (3-dodecylthiophene) and poly(hexadecylthiophene) has been studied. A direct dependence of the diffusion rate on the alkyl group lengths was ascertained. The diffusion rate could be increased by irradiation of the polymers. 相似文献
DSA metal oxide electrodes such as the RuO(2)/IrO(2)/TiO(2) mixed system are widely studied for their excellent electrocatalytic activity. In order to understand their catalytic properties, the comprehension of the surface chemistry involved during electrochemical treatments is crucial. With this aim, RuO(2)/IrO(2)/TiO(2) mixed-oxide electrodes having various noble metal contents were studied by means of secondary ion mass spectrometry (SIMS). In particular, cathodic and anodic polarization and O(2) evolution reactions were carried out to test the electrode behaviour and SIMS analyses were performed after all these treatments. In this way, surface changes induced by electrochemical treatments and depending on electrode composition were widely investigated by SIMS, revealing, for example, the presence of hydration or preferential dissolution phenomena induced by electrochemical processing. 相似文献
A thin film of mixed-valent CuPtCl6 is deposited on a glassy carbon electrode by continuous cyclic scanning in a solution containing 3×10−3 M CuCl2+3×10−3 M K2PtCl6+1 M KCl in the potential range from 700 to −800 mV. The cyclic voltammetry is used to study the electrochemical behaviors of nitrite on CuPtCl6/GC modified electrode and the electrode displays a good catalytic activity toward the oxidation of nitrite. The effects of the film thickness, pH, the electrode stability and precision have been evaluated. Experiments in flow-injection analysis are performed to characterize the electrode as an amperometric sensor for the detection of nitrite. The modified electrode shows a wide dynamic range, quite a low detection limit and short response time. The linear relationship between the flow-injection peak currents and the concentrations of nitrite is at a range of 1×10−7–2×10−3 M with a detection limit of 5×10−8 M. 相似文献
A conducting polymer composite was prepared from nano-sized hydroxyaptite (nHAp) doped into poly(3,4-ethylenedioxythiophene) (PEDOT) and then electrodeposited on a glassy carbon electrode (GCE). The nHAp carries carboxy groups and therefore is negatively charged at moderate pH value. When doped into PEDOT (PEDOT-nHAp), it forms a uniform and stable film that exhibits low electrochemical impedance, a large specific surface, and high activity toward the electrochemical oxidation of nitrite. Under optimized conditions and at a relatively low working potential of 0.78 V (vs. SCE), the modified GCE exhibited a linear amperometric response in the 0.25 μM to 1.05 mM nitrite concentration range, and the limit of detection is as low as 83 nM.
Atomistic simulations were performed on poly(N-vinyl-2-pyrrolidone) (PVP) and its blends with chitosan (CS) in different ratios using molecular mechanics (MM) and molecular dynamics (MD) simulations in three-dimensionally periodic and effective two-dimensionally periodic condensed phases. Four independent microstructures were generated to analyze their surface properties. The calculated surface-energy values for PVP compared quite well with the experimental data reported in the literature. The density profile was analyzed, and the structure of the films showed an interior region of the bulk density. Various components of the energetic interactions (torsional, van der Waals, etc.) were examined to gain deeper insight into the nature of regular and anomalous interactions between the bulk and the surface films. Surface energies of PVP/CS blends were computed by MD simulations using the bulk pressure-volume-temperature (PVT) parameters. Bulk properties such as the cohesive energy density (CED) and solubility parameter (delta) were calculated using MM and MD simulations in the NVT ensemble under periodic boundary conditions. The Flory equation of state was used to compute the thermal expansion coefficient as well as PVT parameters. These surface-energy values agreed well with the surface-energy data calculated using the Zisman equation, which were also in accordance with the experimental observations. The results from this study suggest that computer simulations would provide valuable information on polymers and polymer-blend surfaces. 相似文献
In this study, Pd/Nafion electrodes were prepared by impregnation-reduction methods in sensing oxygen. To prolong the electrode's
life in practical use, a polypyrrole (PPy) film was chemically deposited onto the Pd/Nafion electrode. The sensitivities of
PPy-modified Pd/Nafion electrodes are 0.00671 and 0.0117 μA/ppm obtained in O2 concentration regions of 0–5000 and 5000–50,000 ppm, respectively. Generally, the response time and the recovery time decreases
and increases significantly with increasing O2 concentrations. After continuous aging tests for 48 h, the sensitivities of the Pd/Nafion and the PPy-modified Pd/Nafion
electrodes decrease by 97% and 53%, respectively.
Electronic Publication 相似文献
A cobalt hexacyanoferrate (CoHCF)-modified graphite paraffin wax composite electrode was prepared by a new approach. An amine-functionalised
graphite powder was used for the fabrication of the electrode. A functionalised graphite paraffin wax composite electrode
was prepared and the surface of the electrode was modified with a thin film of CoHCF. Various parameters that influence the
electrochemical behaviour of the modified electrode were studied by varying the background electrolytes, scan rates and pH.
The modified electrode showed good electrocatalytic activity towards the oxidation of butylated hydroxyanisole (BHA) under
optimal conditions and showed a linear response over the range from 7.9 × 10−7 to 1.9 × 10−4 M of BHA with a correlation coefficient of 0.9988. The limit of detection was 1.9 × 10−7 M. Electrocatalytic oxidation of BHA was effective at the modified electrode at a significantly reduced potential and at
a broader pH range. The utility of the modified electrode as an amperometric sensor for the determination of BHA in flow systems
was evaluated by carrying out hydrodynamic and chronoamperometric experiments. The modified electrode showed very good stability
and a longer shelf life. The modified electrode was applied for the determination of BHA in spiked samples of chewing gum
and edible sunflower oil. The advantage of this method is the ease of electrode fabrication, good stability, longer shelf
life, low cost and its diverse application for BHA determination.
Figure Cyclic Voltammogram of () CoHCF modified electrode, () in presence of 1.9 x 10−5 M of BHA and () bare electrode, () in the presence of 1.9 x 10−5 M of BHA in 1.0 M NaCl, pH 7.0 相似文献
The authors describe a composite material prepared from carbon nanohorns and poly(2-aminopyridine) that was obtained by electrochemical polymerization of 2-aminopyridine on carbon nanohorns. The material was used to modify a glassy carbon electrode (GCE) to obtain a sensor for non-enzymatic determination of hydrogen peroxide. The modified GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The modified electrode is shown to display excellent electrical conductivity and catalytic activity towards hydrogen peroxide, mainly due to the large specific surface area of carbon nanohorns, the good electron charge transfer properties resulting from the use of poly(2-aminopyridine), and their synergistic effect. The response of the modified GCE (best operated at a working potential of ?0.45 V vs. SCE) to H2O2 is linear in the 0.05 to 8 mM concentration range. The limits of detection (LOD) and quantitation (LOQ) are 3.6 μM and 12.4 μM, respectively. The electrode is selective, stable and reproducible, this making it a promising tool for non-enzymatic determination of hydrogen peroxide.
Inclusion complex of ferrocene (Fc) with beta-cyclodextrin (beta-CD) has been synthesized in ethylene glycol. It was unsolvable in water and had been successfully used to the preparation of beta-CD-Fc inclusion complex modified carbon paste electrode (CFCPE). Solid paraffin was used as the binder of the electrode. Ascorbic acid (AA) was electrocatalytically oxidized at the electrode in NH(3)-NH(4)Cl buffer (pH 10.0) with a anodic peak potential of +0.20 V (vs. SCE). The anodic current was proportional to the concentration of AA in the range 1.0x10(-3)-5.0x10(-7) mol l(-1) with the detection limit of 1.0x10(-7) mol l(-1). Using the inclusion complex as the electroactive substance greatly increased the stability and reproducibility of CFCPE than using Fc; the lifetime of the electrode can be over 1 year. Because CFCPE responds rapidly and sensitively, it has been successfully applied to the determination of AA in fruit juices. 相似文献
The proposed work describes a simple spectrophotmetric as well as a titrimetric method to determine sulfur dioxide. The spectrophotometric method is based on a redox reaction between sulfur dioxide and iodine monochloride obtained from iodine with chloramine-T in acetic acid. The reagent iodine monochloride oxidizes sulfur dioxide to sulfate, thereby reducing itself to iodine. Thus liberated iodine will also oxidize sulfur dioxide and reduce itself to iodide. The obtained iodide is expected to combine with iodine to form a brown-colored homoatomictriiodide anion (460 nm), which forms an ion-pair with the sulfonamide cation, providing exceptional color stability to the system under an acidic condition, and is quantitatively relatd to sulfur dioxide. The system obeys Beer's law in the range 5 - 100 microg of sulfur dioxide in a final volume of 10 ml. The molar absorptivity is 5.03 x 10(3) l mol(-1)cm(-1), with a relative standard deviation of 3.2% for 50 microg of sulfur dioxide (n = 10). In the titrimetric method, the reagent iodine monochloride was reduced with potassium iodide (10%) to iodine, which oxidized sulfur dioxide to sulfate, and excess iodine was determined with a thiosulfate solution. The volume difference of thiosulfate with the reagent and with the sulfur dioxide determined the sulfur dioxide. Reproducible and accurate results were obtained in the range of 0.1 - 1.5 mg of sulfur dioxide with a relative standard deviation of 1.2% for 0.8 mg of sulfur dioxide (n = 10). 相似文献