An enzyme electrode for the amperometric determination of glucose

An amperometric method utilizing a glucose electrode has been developed for the determination of blood glucose. The time of measurement is less than 12 s if a kinetic method is used and 1 min if a steady-state method is used. The long-term stability of the electrode is ca. 0.1% change from maximum response per day when stored at room temperature for over 10 months. The enzyme electrode determination of blood sugar compares favorably with commonly used methods with respect to accuracy, precision, and stability. The only reagent required for blood sugar determinations is a buffer solution. The electrode consists of a metallic sensing layer covered by a thin film of immobilized glucose oxidase held in place by means of cellophane. When poised at the correct potential, the current produced is proportional to the glucose concentration.     

An amperometric enzyme electrode for the determination of 3alpha-hydroxysteroids

An enzyme electrode for quantifying the total content of 3alpha-hydroxysteroids is described. 3alpha-Hydroxysteroid dehydrogenase (E.C. 1.1.1.50) was immobilized on the surface of glassy-carbon and low-temperature isotropic-carbon electrodes by intermolecular cross-linking with bovine serum albumin and glutaraldehyde. The effects of the following factors on the response to androsterone were studied: applied potential, the concentration and pH of the pyrophosphate buffer used, and the NAD concentration. The Michaelis-Menten constant for 3alpha-hydroxysteroid dehydrogenase in solution was determined amperometrically with androsterone as substrate (K(m) = 189muM). A preliminary report of the response of the system to serum samples containing a bile acid is presented.     

Mixed ferrocene-glucose oxidase-carbon-paste electrode for amperometric determination of glucose

The simultaneous incorporation of ferrocene derivatives and glucose oxidase into a carbon-paste matrix results in an effective microelectrode for sensing glucose. The close proximity of the enzymatic, redox mediating and sensing sites offers extremely short response times (t_95%=18 s) compared with early ferrocene-based glucose sensors. Several ferrocene derivatives are evaluated, with 1,1′-dimethylferrocene yielding the best results. The influence of the paste composition, operating potential, glucose concentration and other variables is described. The incorporation of stearic acid into the enzyme-containing paste greatly reduces the interference due to ascorbic acid. The microelectrode is easily fabricated, as time-consuming multi-step immobilization schemes are eliminated. Flow-injection measurements at a rate of 90 samples per hour and relative standard deviations of 3% are also reported.     

Flow-injection amperometric determination of chlorine at a gold electrode

The applied potential is +0.2 V vs. SCE, flow rate is 1 ml min^?1 and sample volume is 30 μ1. The background electrolyte is 0.05 M phosphate, pH 7.4. Electrode pretreatment is +1.3 V vs. SCE for 40 s, followed by a pre-injection delay of 20 s. Peak current over a receding baseline is used. Linear range extends down to 0.4 μM for chloramine and 0.2 μM for hypochlorite. Sensitivities are 70 and 95 nA μM^? respectively. Time per determination is less than 1.5 min. Monochlorinated glycine is active whereas chlorinated cyanuratesshow no response. Chlorine and monochloramine in river water were determined.     

A novel two-enzyme amperometric electrode for lactose determination.

Coimmobilization of beta-galactosidase and glucose oxidase in a redox polymer, polyvinylferrocenium perchlorate (PVF+ ClO4-), led to the development of an enzyme electrode for the determination of lactose. The amperometric response of the electrode was measured at +0.70 V vs. SCE, which was due to the electrooxidation of enzymatically produced H2O2. The effects of the substrate and buffer concentrations as well as the pH on the electrode response were elucidated.     

A new catalytic electrode for the amperometric determination of hydrogen peroxide

The electrode is based on the decomposition of H₂O₂ by an inorganic polymer catalyst. The steady -state decomposition currents of H₂0₂ obtained with the catalyst electrode are independent of ionic strength (0.1–1.5) and pH (2.5–10.5). A linear relationship is obtained from 0.02 to 2 mM H₂0₂ in 0.1 M KCl at 25°C.     

Carbon paste-tetrathiafulvalene amperometric enzyme electrode forthe determination of glucose in flowing systems

The development of a carbon paste-tetrathiafulvalene amperometric enzyme electrode for the determination of glucose in flowing streams is described. The enzyme electrode is operated in a flow-through detector based on the wall-jet configuration under flow injection (FI) and steady-state (SS) conditions. Under FI conditions, high precision (0.6%) and sample throughput (120 samples h-1) are possible. Moreover no pre-conditioning of the electrode is required. The flow system is suitable for the determination of glucose in whole blood without sample dilution. With proper orientation of the jet with respect to the enzyme electrode, high accuracy can be obtained under SS conditions.     

Electrocatalytic amperometric determination of amitrole using a cobalt-phthalocyanine-modified carbon paste electrode

Cobalt-phthalocyanine-modified carbon paste electrodes are shown to be excellent indicators for electrocatalytic amperometric measurements of triazolic herbicides such as amitrole, at low oxidation potentials (+0.40 V). The detection and determination of amitrole in flow injection analysis with a modified carbon paste electrode with Co-phthalocyanine is described. The concentrations of amitrole in 0.1 M NaOH solutions were determined using the electrocatalytic oxidation signal corresponding to the Co(II)/Co(III) redox process. A detection limit of 0.04 microg mL(-1) (4 ng amitrole) was obtained for a sample loop of 100 microL at a fixed potential of +0.55 V (vs. Ag/AgCl) in 0.1 M NaOH and a flow rate of 4.0 mL min(-1). Furthermore, the modified carbon paste electrodes offers reproducible responses in such a system, and the relative standard deviation was 3.3% using the same surface, 5.1% using different surface, and 6.9% using different pastes. The performance of the cobalt-phthalocyanine-modified carbon paste electrodes is illustrated here for the determination of amitrole in commercial formulations. The response of the electrodes is stable, with more than 80% of the initial retained activity after 50 min of continuous use.     

Sensitive capillary electrophoretic determination of mercury species with amperometric detection at a copper electrode after cation exchange preconcentration

A capillary electrophoretic method for the separation of four mercury species with amperometric detection was developed. Inorganic Hg2+, methyl-, ethyl-, and phenyl-mercury were complexed with L-cysteine and separated in a counterelectroosmotic mode in an electrolyte solution comprised of 20 mM sodium tetraborate at pH 9.5. Amperometric detection of separated species was achieved at passivated copper electrode under electrocatalytic oxidation conditions. The four mercury species were separated in less than 8 min with LODs ranging from 170 to 450 microg/L. Cation exchange preconcentration was used to decrease the LODs down to 1.7 microg/L.     

Voltammetric and amperometric determination of metoclopramide on boron-doped diamond film electrode

New methods for the determination of metoclopramide, antiemetic and gastroprokinetic pharmaceutical, were developed, using differential pulse voltammetry (DPV) and flow injection analysis (FIA) with amperometric detection on a boron-doped diamond film electrode. Electrode pretreatment necessary to ensure the stable results was investigated and it was found, that while DPV requires frequent electrode cleaning, FIA with a sufficiently high flow rate can maintain a stable signal with no signs of electrode passivation. The calculated quantification limits of the DPV and FIA with amperometric detection were 0.13 μmol L⁻¹ and 0.015 mmol L⁻¹, respectively. The applicability of the new methods was verified by the determination of metoclopramide in a pharmaceutical preparation. FIA with amperometic detection proved to be sensitive, accurate and, due to the resistance of the electrode to the passivation, also simple to handle.      

Mediated amperometric enzyme electrode incorporating peroxidase for the determination of hydrogen peroxide in organic solvents

An amperometric enzyme electrode incorporating horseradish peroxidase is described for the determination of hydrogen peroxide in organic solvents. The enzyme was co-adsorbed with an electron mediator, potassium hexacyanoferrate(II), on the surface of a graphite foil electrode, making reagentless measurement possible. The electrochemical reduction of the enzymatically oxidized mediator was utilized as the analytical signal. Studies in different solvent systems revealed that the electrode could be operated in dioxane, chloroform and chlorobenzene, the last two providing approximately double the sensitivity of the former. The presence of a small amount of aqueous buffer was essential for sensor activity. During 2 weeks of intermittent use, the sensitivity of the electrode decreased to 40% of its initial value. At least 50 assays could be performed with a single sensor.     

Sol-gel derived metal dispersed ceramic-graphite composite electrode for amperometric determination of dopamine

A new silver dispersed composite electrode made of sol-gel derived ceramic-graphite has been demonstrated for the determination of dopamine. Silver has been immobilized within the porous and rigid silicate network in the composite by the specific interaction with (3-mercaptopropyl)trimethoxysilane (MPS). The modified composite electrode coated with Nafion exhibited good catalytic activity for the oxidation of dopamine at a reduced potential of 0.35 V with good sensitivity and selectivity. The sensor showed a linear response to dopamine in the concentration range from 6.6×10⁻⁶ to 1.2×10⁻³ M with a correlation coefficient of 0.9987. The electrode surface can be easily renewed by a simple mechanical polishing and has the advantages of good reproducibility, rapid response and remarkable stability.     

Flow injection determination of ergonovine maleate with amperometric detection at the Kel-F-graphite composite electrode

The Kel-F-graphite electrode was used for the electrochemical detection of ergonovine maleate in a flowing stream. It was found useful in the analyte concentration range 0.5-20 mug ml , with a detection limit of 50 ng ml (1.1 x 10(-7)M). A procedure was developed for assay of ergonovine maleate in tablets, and the results obtained agreed with those given by the official U.S. Pharmacopeia method.     

beta-Cyclodextrin-ferrocene inclusion complex modified carbon paste electrode for amperometric determination of ascorbic acid

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.     

HPLC with amperometric detection for the determination of pesticides of high polarity

A relatively simple procedure is described for the selective and highly sensitive determination of amitrole (3-amino-1,2,4-triazole) by ionpair HPLC with amperometric detection. The separation was achieved on a polar CN-column using hexane, propanol, water (62:36:2) with LiClO₄ (2.5 g·l^–1) and trichloroacetic acid (2 g·l^–1) as electrolytes. The determination range lies between 500 pg and 500 ng and the limit of detection was found to be 200 pg (s.d.: 11%; N=9). The minimum detectability for the alternative UV-monitoring was 2.5 ng. The developed method may be helpful in production and quality control and for the selective determination of amitrole in commercial formulations.     

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.     

A chromatographic determination of nitrate with amperometric detection at a copperized cadmium electrode

A copperized cadmium flow-through electrode is applied for cathodic detection of nitrate in the effluent stream of a liquid chromatograph. The nitrate is separated from dissolved oxygen in a small (10 cm) column of strong-base, anion-exchange resin (Dowex 1-X8) with 5 mM perchloric acid as the eluent. The effluent stream is buffered to pH 8 by mixing with a stream of buffer prior to detection. A large excess of chloride added to the sample dramatically improves the separation of nitrate from dissolved oxygen in the sample.     

强电离放电等离子体中活性物种的检测

利用氧化还原滴定法检测了强电离放电等离子体中活性物种,用以衡量等离子体的表观氧化能力。分别考察了pH值、放电气体流量、放电功率、放电气体压力、反应时间等因素对检测的影响。在pH＝6.0,反应时间3 min优化条件下,随放电功率增加,等离子体中活性物种浓度增加;放电气体流量增加,等离子体中活性物种浓度下降;放电气体压力增加,等离子体中活性物种浓度增加。本方法设备简单、再现性好,灵敏度高,检出限为3.91×10^-5 mol/L。