Evaluation of a mechanically immobilized nickel hexacyanoferrate electrode as an amperometric sensor for thiosulfate determination

A nickel hexacyanoferrate modified electrode was constructed by mechanical immobilization. A reversible peak with midpoint potential of 0.38 V was observed in cyclic voltammetry with 0.1 M NaNO₃. Electrocatalytic oxidation of thiosulfate was effective on the modified electrode at a significantly reduced overpotential of 0.5 V and at broad pH range. The modified electrode can be used for the determination of thiosulfate in the concentration range of 7.0 × 10^–4 to 5.6 × 10^–3 M. It has been used for the amperometric determination of thiosulfate in photographic effluents. The results obtained were in good agreement with those obtained by other methods.     

Mechanically immobilized nickel aquapentacyanoferrate modified electrode as an amperometric sensor for the determination of BHA

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.     

Evaluation of a mechanically immobilized nickel hexacyanoferrate electrode as an amperometric sensor for thiosulfate determination

A nickel hexacyanoferrate modified electrode was constructed by mechanical immobilization. A reversible peak with midpoint potential of 0.38 V was observed in cyclic voltammetry with 0.1 M NaNO₃. Electrocatalytic oxidation of thiosulfate was effective on the modified electrode at a significantly reduced overpotential of 0.5 V and at broad pH range. The modified electrode can be used for the determination of thiosulfate in the concentration range of 7.0 × 10^–4 to 5.6 × 10^–3 M. It has been used for the amperometric determination of thiosulfate in photographic effluents. The results obtained were in good agreement with those obtained by other methods. Received: 27 January 1999 / Revised: 5 July 1999 / Accepted: 7 July 1999     

Flow-injection amperometric determination of oxalate with immobilized oxalate oxidase

Oxalate is immobilized on controlled-pore glass and is used on-line in a glass minicolumn (2.5×25 mm). The hydrogen peroxide formed is detected amperometrically. Oxalate (6×10^?6?9×10^?4 M) is determined in a flowing stream of pH 3.5 citrate (or succinate) buffer. As little as 20 ng (in 40 μl; 5.7×10^?6 M) of oxalate can be detected. Copper inhibition can be removed either by adding EDTA to the carrier stream or incorporating a chelating-resin minicolumn into the flow system prior to the enzyme column.     

Flow injection determination of choline in milk hydrolysates by an immobilized enzyme reactor coupled to a selective hydrogen peroxide amperometric sensor

A choline oxidase (ChO) immobilized enzyme reactor (IMER) prepared by glutaraldehyde coupling of the enzyme on aminopropyl modified controlled pore glass beads is described. The ChO-IMER was coupled, in a flow injection configuration system, to an interference free hydrogen peroxide amperometric sensor based on a Pt surface modified by an overoxidized polypyrrole film. The resulting analytical device responds selectively to choline and displays a sensitivity of 46.9 ± 0.2 μC mM⁻¹ and a limit of detection, calculated at a signal-to-noise ratio equal to 3, of 7 μM. Sensitivity remains constant for about 20 days and then starts to slowly deteriorate and after 2 months a 70% of the initial sensitivity was still retained. The application to choline determination in milk hydrolysates is demonstrated. Short- and long-term drift observed in the analytical response can be corrected by a bracketing technique.     

An amperometric sensor for carbon dioxide based on immobilized bacteria utilizing carbon dioxide

A biosensor consisting of a CO₂-utilizing autotrophic bacterium (strain S-17, Pseudomonas type) and an oxygen-sensing electrode was constructed for the amperometric determination of CO₂. The correlation between current decrease and CO₂ concentration was linear in the range 5–200 mg l^?1 CO₂. The optimum temperature and pH for operation of the biosensor were 30°C and 5.5, respectively. The sensor did not respond to other volatile compounds except for acetic acid. The sensor could be operated continuously for about a month.     

A novel palygorskite-modified carbon paste amperometric sensor for catechol determination

A palygorskite-modified carbon paste electrode (CPE) was constructed using graphite powder mixed with palygorskite particles. Compared with the unmodified CPE, the resulting palygorskite-modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the palygorskite exhibits catalytic activity to catechol and significantly improves the determining sensitivity. The electrocatalytic activity of palygorskite is attributed to its high adsorption capability and the –OH groups on its surface, which plays an important role in the electron transfer between the modified CPE and the catechol in the solution. The sensor shows a linear response range between 5 and 100 μM catechol with a correlation coefficient of 0.998. The detection limit was calculated as 0.57 μM (s/n = 3).     

A novel amperometric sensor and chromatographic detector for determination of parathion

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.     

TNT determination based on its degradation by immobilized HRP with electrochemical sensor

Based on the mechanism of 2,4,6-Trinitrotoluene (TNT) degradation, an amperometric hydrogen peroxide biosensor was constructed for the determination of trace amounts of TNT by immobilization of MWCNTs, HRP and Nafion onto the surface of glassy carbon electrode (GCE). The Nafion/MWCNTs/HRP biosensor was capable of degrading TNT with the consumption of H₂O₂ and HRP in 0.2 mol/L PBS (pH 7.0). Trace TNT was quantitative analyzed by the current decrease of H₂O₂ at the reductive potential of −0.35 V using cyclic voltammetry (CV). Effect of the ratio of MWCNTs/HRP, initial concentration of H₂O₂ and electrolyte’s pH were also optimized by CV. Under the optimal conditions, the current decrease of H₂O₂ that was consumed by TNT degradation was proportional to TNT ranging from 8.8 × 10⁻⁹ mol/L to 2.64 × 10⁻⁷ mol/L with a detection limit of 3.0 × 10⁻⁹ mol/L (S/N = 3). It developed a new way for simple, rapid and sensitive measurement of trace TNT.     

A regenerable immobilized nadh model IV: Reduction of pyridine-2-carbaldehyde by immobilized 1,4-dihydronicotinamide in the presence of Mg2+ ions

Dihydronicotinamide, anchored to a macroreticular polystyrene resin, reduces pyridine-2-carbaldehyde (PCA) in the presence of Mg²⁺ ions in acetonitrile. The reactions are clean at room temperature, the high rate precluding complications arising from slow side reactions. The influence of Mg²⁺ concentration on the rate of reduction of PCA by polymer-bound reagent and BNAH (1-benzyl-1,4-dihydronicotinamide; low-molar-mass analog) has been studied. Analysis of the kinetic data showed that of the processes contributing to the overall reduction, the reaction between the reductant and the complexed substrate proceeded at the highest rate. In the polymer-bound reagent, “site isolation” on the rigid matrix was observed to prevent bimolecular disproportionation of the neighboring dihydronicotinamides. Regeneration of the polymeric reagent was achieved with an efficiency of 98% per cycle.     

Condition optimization of amperometric determination of chemical oxygen demand using boron-doped diamond sensor

The amperometric determination of chemical oxygen demand (COD) reported by Quan Xie??s group (Electrochem Commun 9:2281, 14), was a rapid, green and simple COD evaluation method. This work focused on testing and verifying this method by using a home-made boron-doped diamond (BDD) film as anode and optimizing the experiment conditions. The BDD thin film electrode was employed as anode and the electrochemical process was run with different experimental parameters including counter electrode, electrode gap, applied potential, electrolyte pH, and temperature. Standard samples were determined in the optimum conditions, a linear range of 19.2?C11,600?mg l^?1 COD and a low detection limit of 0.192?mg l^?1 COD were well established with the present approach. The COD value of the simulated organic wastewater determined by this method agreed well with the standard dichromate method, and it showed good accuracy, stability, and reproducibility.     

Morphology determination of small particles by electron microscopy and electrical conduction measurements

In this paper, we show that it is possible to deduce the actual morphology of small particle condensed onto an insulator by combining the granularity analysis from electron micrographs and the electrical sheet conductance of the deposit on its substrate. Assuming the particles are truncated ellipsoids, we determine the excentricity and the contact angle with the substrate for Au on amorphous carbon and MgO substrates.     

S-nitrosothiol detection via amperometric nitric oxide sensor with surface modified hydrogel layer containing immobilized organoselenium catalyst

A novel electrochemical device for the direct detection of S-nitrosothiol species (RSNO) is proposed by modifying an amperometric nitric oxide (NO) gas sensor with thin hydrogel layer containing an immobilized organoselenium catalyst. The diselenide, 3,3'-dipropionicdiselenide, is covalently coupled to primary amine groups in polyethylenimine (PEI), which is further cross-linked to form a hydrogel layer on a dialysis membrane support. Such a polymer film containing the organoselenium moiety is capable of decomposing S-nitrosothiols to generate NO(g) at the distal tip of the NO sensor. Under optimized conditions, various RSNOs (e.g., nitrosocysteine (CysNO), nitrosoglutathione (GSNO), etc.) are reversibly detected at 相似文献   

Sub-millimolar determination of formalin by pulsed amperometric detection

Formalin, formaldehyde in the presence of methanol, was determined by pulsed amperometric detection (PAD). A triple waveform using E_det=−0.3 V (t_det=30 ms), E_oxd=+0.8 V (t_oxd=200 ms), and E_red=−0.8 V (t_red=350 ms) versus Ag/AgCl was applied at a Au electrode for detection in a flow injection (FI) system. The approach was rapid and yielded a sub-millimolar detection limit (0.0129 mM) with a dynamic range up to 100 mM. A precision of 8.8% R.S.D. at 1.0 mM for two hundred repetitive injections by the FI-PAD was obtained, whereas holding at a constant potential (−0.3 V versus Ag/AgCl) for anodic oxidation of formaldehyde caused the response to decrease dramatically after a few measurements. The method developed was used to analyze the formalin contents of water from rinsed samples of vegetables and fruit and ice-melt from seafood, and the method showed good agreement with the liquid chromatography (LC) method.     

Fibre optic sensor with bio-membrane supported immobilized morin for aluminium determination

A new type of fibre optic sensor based on the use of bio-membrane is proposed for the determination of aluminium. Morin is immobilized on mutton membrane pre-treated with formaldehyde and attached to the fibre optic. Fluorescence response is linear from 8 × 10^–7 to 3 × 10–5M. The detection limit is 6 × 10^–7 M. Response time is 30—60 s.     

Flow-injection determination of starch and total carbohydrate with an immobilized glucoamylase reactor and pulsed amperometric detection

Starch and total carbohydrate are determined by using a flow-injection system comprised of an immobilized glucoamylase reactor followed by pulsed amperometric detection of the glucose produced. Glucoamylase, immobilized onto porous silica and packed into a short stainless steel column, is capable of nearly quantitative (98%) conversion of the starch to glucose. The sensitivity of pulsed amperoemtric detection for soluble starch is increased 26-fold by first passing the starch through the immobilized glucoamylase reactor. This system is successfully used to determine total carbohydrate in beer samples. The method is simple, rapid and sensitive for starch.     

Chemiluminescence flow sensor for the determination of ascorbic acid with immobilized reagents

A novel flow sensor based on chemiluminescence (CL) for the determination of ascorbic acid has been proposed. The analytical reagents, luminol and ferricyanide, were both immobilized on an anion-exchange resin column. The CL signal produced by the reaction between luminol and ferricyanide, which were eluted from the column through sodium phosphate injection, was decreased in the presence of ascorbic acid. The CL emission intensity was linear with ascorbic acid concentration in the range 0.01-0.8 mug ml(-1); the detection limit was 5.5 x 10(-3) mug ml(-1). The whole process, including sampling and washing, could be completed in 1 min with a relative standard deviation of less than 5%. The sensor could be reused more than 100 times and has been applied successfully to the analysis of ascorbic acid in pills and vegetables.     

Nitric oxide determination by amperometric carbon fiber microelectrode

Nitric oxide (NO) amperometric microsensor was prepared by the modification of bare carbon fiber electrode by Nafion and cellulose acetate (CA). Detection limit, response time, reproducibility and influence of some possible interferences (nitrite, nitrate, arginine) were tested and evaluated. This sensor was used for in vitro determination of NO release from fresh porcine aorta induced by calcium ionophore A23187 (CI).     

Flow-injection amperometric determination of pesticides on the basis of their inhibition of immobilized acetylcholinesterases of different origin

Determination of the organophosphorus pesticides paraoxon, chlorpyrifos oxon, and malaoxon has been performed by a method based on inhibition of acetylcholinesterase (AChE) and amperometric detection in a flow-injection system with enzymes obtained from the electric eel (eeAChE) and Drosophila melanogaster (dmAChE) and immobilized on the surface of platinum electrode within a layer of poly(vinyl alcohol) bearing styrylpyridinium groups. dmAChE is more sensitive than eeAChE to inhibition by chlorpyrifos oxon and paraoxon. The sensitivity difference was largest for chlorpyrifos oxon (detection limit approx. 17 times lower), and practically none for malaoxon. Determination of the analytes in spiked river water samples by use of the dmAChE biosensor resulted in recoveries from 50 to 90 % for chlorpyrifos oxon at levels of 20 to 40 nmol L(-1), 50 to 100 % for paraoxon at 0.6 to 0.8 micro mol L(-1), and 140 to 190 % for malaoxon at 0.6 to 1.2 micro mol L(-1).     

Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system

A flow-injection system is proposed for the simultaneous determination of sulfite and phosphate in wine. A sulfite oxidase immobilized reactor and purine nucleoside phosphorylase-xanthine oxidase co-immobilized reactor are incorporated at fixed positions (parallel configuration) in the flow line, which is based on the splitting of the flow after sample injection and subsequent confluence. A poly(1,2-diaminobenzene)-coated platinum electrode is used as an amperometric detector to detect selectively hydrogen peroxide generated enzymatically in the enzyme reactors, without any interference from oxidizable species and proteins present in wine. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to sulfite and the second peak to phosphate. The peak current is linearly related to the concentrations of sulfite between 1 × 10⁻⁵ and 2 × 10⁻³M and phosphate between 2 × 10⁻⁵ and 5 × 10⁻³M. The simultaneous determination of sulfite and phosphate in wine can be performed at a rate of 30 samples/hr with satisfactory precision (less than 1.2% RSD) and no pretreatment except for the sample dilution.