Continuous Amperometric Determination of Glucose Using an Immobilized Enzyme Reactor in Combination with an Immersible Dialysis Probe

Abstract

Glucose was continuously determined by reaction in a packed-bed enzyme reactor containing glucose oxidase and catalase. Oxygen consumption was measured amperometrically with a polarographic Clark electrode. Glucose was sampled through a dialysis probe immersed in the solution to be measured. An extension of the normal range for the enzyme was achieved by modulating the flow rate through the dialysis probe and a linear response was obtained in the range of 1.0-60 mM glucose. The correlation between the glucose transfer and the membrane area of the dialysis probe was also studied. Six different membranes were used, all showing variations in the adhesion of yeast cells.     

The Application of an Enzyme Electrode for Blood Glucose Determination in the Automated Flow System

Abstract

An enzyme electrode containing immobilized GOD was utilized in a continuous flow system for the automatical determination of glucose. The advantages of kinetic measurement of H₂ O ₂ are used. Characteristic parameters of device and results in routine are shown. Particular advantages are: low requirement on material (20 μl blood, < l μg GOD/measurement) and time (60 samples/h at 15 sec response time) as well as sufficient precision and accuracy (S % - serial: < 2 %).     

Sulfite Determination with Gold Electrode Promoted by bis(4-Pyridyl)disulphide/cytochrome C

Abstract

A biosensor was developed using oxidized cytochrome C - sulfite reaction by following the electrochemical reaction between reduced cytochrome C and gold electrode. The change in the current at the fixed potential equal to anodic peak potential of cytochrome C was proportional to sulfite concentration in the range of 0.4×10^?4 to 4.0×10^?4 M.     

Mediated Enzyme Electrode for the Determination of L-Glutamate

Abstract

A mediated enyme electrode was developed for the determination of L-glutamate, based on the immobilization of L-glutamate oxidase from Streptomyces sp. X 119–6. A graphite working electrode was used with 1,1 dimethylferrocene (DMF) as electron mediator. The electrode responded linearly to L-glutamate over the range 0.2 to 2 mM (0.029–0.29 g/l). The enzyme electrode was applied to the measurement of L-glutamate in various foodstuffs.     

Amperometric Sensor and Immobilized Enzyme Electrode for the Determination of Enzymatic Activities

Abstract

A sensitive method for the rapid determination of activities of soluble or immobilized enzymes, based on the electrochemical detection of hydrogen peroxide is described. Kinetic studies (Vmax and K_M determinations) can be performed for all H₂O₂ generating enzymes (i.e. most of the oxidases) using an amperometric probe with a platinum anode at a fixed potential.

When associated with an immobilized glucose oxidase membrane, this sensor constitutes a glucose electrode and the activity of any hydrolase which releases glucose can be measured. There is no need for other auxiliary enzymes and no preincubation step is required. The possibility to carry out continuous analysis constitutes the main advantage of the described method.     

Kinetic Analysis of an Enzyme-containing Polymer Modified Electrode

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Application of the Iodide Ion-Selective Electrode in the Potentiometric Determination of Chloral Hydrate

Abstract

A simple and sensitive micro method for chloral hydrate determination based on oxidation with iodine in chloroform solution is described. The produced iodide ion in the extract is determined using the iodide ion-selective electrode by either a direct measurement, standard addition technique or potentiometric titration with standard silver nitrate solution. Samples containing 0.1 - 4.0 mg chloral hydrate are analyzed with an average recovery of 99-9% and standard deviation of 0.1%.     

Electrocatalytic Oxidation of Sulfite on a Nickel Aquapentacyanoferrate Modified Electrode: Application for Simple and Selective Determination

An electroactive metal cyanometallate complex, nickel aquapentacyanoferrate (NAPCF) was synthesized and characterized using XRD and UV‐vis spectral studies. The solid complex was then mechanically immobilized on the surface of a paraffin impregnated graphite electrode (PIGE) and the NAPCF modified electrode was characterized using cyclic voltammetry. The dependence of the modified electrode was tested in terms of supporting electrolyte, scan rate and pH of the medium. The electrocatalytic oxidation of sulfite at the modified electrode was investigated by cyclic voltammetry, hydrodynamic voltammetry and chronoamperometry techniques. It was found that the NAPCF modified electrode efficiently exhibited electrocatalytic activity for the oxidation of sulfite with relatively high sensitivity, selectivity and long life of activity. Based on the electrocatalytic oxidation, the NAPCF modified electrode was used as a sensor for the determination of sulfite. The linear working range for the determination of sulfite was 2.78×10^?6 M to 3.00×10^?3 M with a detection limit of 9.26×10^?7 M. The electrode was applied for the determination of sulfite in real samples satisfactorily.     

Enzyme Electrode with Collagen-Immobilized Cholesterol Oxidase for the Microdetermination of Free Cholesterol

Abstract

Cholesterol oxidase has been immobililzed on collagen films associated to an electrochemical sensor to form a “cholesterol electrode”. The electrode poised at a potential of + 650 my vs Ag/AgCl detects the hydrogen peroxide produced in the enzymatic reaction. This device presents a very high sensitivity and a wide range of linearity (10^?7 M - 0.8.10^?4 M). The use of a non enzymatic electrode associated with the enzymatic one allowed the detection and correction of electrochemical interferences when applied to human sera for free cholesterol determination.     

Determination of Serum Urea with an Enzyme Thermistor Using Immobilized Urease

Abstract

The application of an enzyme thermistor device in a simple and accurate procedure for the determination of serum urea is described. The enzyme thermistor measures the heat produced when urea is passed through a small column containing immobilized urease. The stability and sensitivity as well as the performance with clinical serum samples of the system is evaluated. Advantages are the simplicity, the low enzyme cost and the insensitivity to the optical properties of the sample and interfering substances, which may affect the commonly used assay procedures.     

A Dual-Enzyme Electrode for the Determination of Flavin Adenine Dinucleotide in the Presence of Riboflavin and Flavin Mononucleotide

Abstract

An electrode method has been developed for the determination of flavin adenine dinucleotide (FAD) using a potentiometric gas sensor and commercially available enzyme preparations. The construction of the FAD-sensitive electrode is based on immobilizing alkaline phosphatase (E.C. 3.1.3.1) and adenosine deaminase (E.C. 3.5.4.4) on the sensing tip of an ammonia gas sensor. Alkaline phosphatase enzymatically catalyzes the hydrolysis of FAD to adenosine which is subsequently converted to ammonia by adenosine deaminase. The response of the dual-enzyme electrode is linear between 8 × 10^?5 M and 4 × 10^?3 M FAD with a slope of 43 mV/decade concentration at pH 8.5 and 37[ddot]C. The optimum buffer system is 0.5 M diethanolamine, 1 × 10^?3 M Tris-HCl and 1 × 10^?3 M MgCl₂. Electrodes constructed with enzymes immobilized by cross-linking with glutaraldehyde and bovine serum albumin showed longer life times than electrodes using enzymes entrapped by a dialysis membrane. The electrode is highly selective over riboflavin and flavin mononucleotide, but it does respond to other nucleotides.     

Determination of Total Phenols in Foods by Boron Doped Diamond Electrode

A robust electrochemical method to measure the total phenol content in food samples is presented. Under optimal condition, BDD electrode showed excellent performance to detect the oxidation of several phenols and does not present the drawback due to electrode fouling. The analytical method used to perform such measurement has been optimized and successfully applied in different food samples. The results obtained were compared with the standard Folin–Ciocalteau method.     

几种粮食中硒含量的测定

采用ＲＦ－５０００型荧光分光光度计测定了几种市售粮食中的硒含量，并对硒与人体健康关系等问题进行了讨论，可作为人们饮食结构中调节硒含量的参考依据。     

Evaluation of a New Method for the Determination of Elements in Vegetable Foods and Feeds by Atomic Absorption Spectroscopy with Sampling of Carbonaceous Slurry

Abstract

The new method, proposed in a preceeding paper for the determination of elements in plant material by flame atomic absorption spectroscopy (FAAS) with liquid sampling of carbonaceous slurry, was tested on other kinds of organic material such as vegetable foods and feeds. Results are reported for the determination of calcium, magnesium, potassium, iron, manganese, zinc and copper in these materials. Also, the analytical results relative to the determination of cadmium by graphite-tube furnace atomic absorption spectroscopy (GTFAAS) for two matrices are given. In all cases accuracy and precision of the analytical procedure were ascertained.     

Electrocatalytic Oxidation and Determination of Sulfite with a Novel Copper‐Cobalt Hexacyanoferrate Modified Carbon Paste Electrode

The electrocatalytic oxidation of sulfite has been studied at a stable electroactive thin film of copper‐cobalt hexacyanoferrate (CuCoHCF) hybrid electrodeposited on a carbon paste electrode (ECMCPE). A linear range of 5 μM to 5 mM of sulfite, with an experimental detection limit of 1 μM, was obtained using the cyclic voltammetric method. The oxidation of sulfite showed no significant fouling effect on the modified electrode surface at sulfite concentrations below 5 mM. The proposed modified electrode exhibited several attractive features, including simple preparation, fast response, good stability and repeatability, and could be applied to sulfite determination in real samples.     

离子色谱法测定魔芋精粉、虾中亚硫酸盐

魔芋精粉和虾样品经水蒸气蒸馏除去杂质的干扰,在密闭容器中对样品进行酸化,在氮气流的保护下蒸馏,用甲醛溶液吸收释放出的二氧化硫,提出了离子色谱法测定样品中亚硫酸盐含量的方法。以IonPacAS9-HC色谱柱,以8mmol.L-1碳酸钠-2.5mmol.L-1氢氧化钠溶液为淋洗液等度洗脱,用电导检测器测定。亚硫酸盐的质量浓度在6.0mg.L-1范围内与其峰面积呈线性关系,方法的检出限(3S/N)为4.0mg.kg-1。方法用于魔芋精粉和虾样品分析,回收率在88.1%～98.3%之间,测定值的相对标准偏差(n=8)在1.4%～6.6%之间。     

A Novel Enzyme Membrane Electrode for Oxalate Determination in Foodstuffs

Abstract

An enzyme membrane electrode usable for the assay of oxalate in foodstuffs is described. A commercially available preactivated polyamide membrane was used for the immobilization of oxalate oxidase. The bioactive disk thus obtained was associated with an amperometric transducer. The resulting self-contained enzyme electrode wich allows oxalate determination in various materials with minimal pretreatment exhibits a linear calibration ranging from 10–7 M and 10–4 M in the cell. The response-time was comprised between 20 seconds and 1 minute, depending on the oxalate content in the sample. The electrode-response was very stable for at least 4 months, a period during which more than 150 assays were performed.

The results obtained with several food materials were in good agreement with those obtained with the conventional spectrophotometric method. Assays were also performed with a microprocessor-based analyzer normally used for glucose measurements with a glucose oxidase electrode When the analyzer is equipped with an oxalate oxidase membrane, without further setting, oxalate can be determined in the range 5 10^?3 M-10^?1 M in the sample.     

Flow Injection Analysis of Lactate and Lactate Dehydrogenase Using an Enzyme Membrane in Conjunction with a Modified Electrode

Abstract

A modified electrode for H₂O₂ oxidation, consisting of Pd/Au sputtered on carbon was covered with a lactate oxidase membrane and used in a FIA manifold for selective determination of lactate. The linear range was 0.01-3 mM lactate and up to 200 samples per hour were measured with a relative standard deviation of 1%. Interferences from ascorbic acid and NADH were small because of the low potential of the modified electrode. The lactate oxidase membrane electrode was also used for measurement of lactate dehydrogenase activity using direct injection of the sample into a carrier stream containing pyruvate and NAD⁺.     

Time Resolved Direct Determination of Arsenate in the Presence of Arsenite on Pencil Graphite Electrode Modified by Graphene Oxide and Zirconium

Trace amount of arsenate in the presence of arsenite was determined directly on pencil graphite electrode modified by graphene oxide and zirconium (Zr−G−PGE). The layer‐by‐layer modification of PGE was characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Key point of the developed method was quick adsorption of arsenate than arsenite on the Zr−G−PGE. In optimal conditions, the Zr−G−PGE was applied for determination of arsenate using differential pulse voltammetry in a linear range 0.10–40.0 μg L⁻¹ with a limit of determination of 0.12±0.01 μg L⁻¹. The sensitivity of the electrode was 1.36±0.07 μA/μg L⁻¹. The modified electrode was used to measure the concentration of arsenate in the river water. A recovery test was performed by introducing 10 μg L⁻¹ arsenate into the rivers water in order and acceptable data of average recovery of 101.2 % was obtained. From the experimental results, the as‐prepared electrode can provide a satisfactory method for direct determination of arsenate in real samples.     

介体型酶电极二级催化反应速度常数的测定

采用开路驰豫法，测定了以二茂铁及其衍生物作为电子传递体的介体型酶电极的均相二级催化反应速度常数，结果表明二甲氨基甲基二茂铁，在绝氧条件下对于酶的再生反应具有高的催化活性，是一种性能优良的电子传递体．此外，讨论了开路弛豫法在酶电极研究中的适用条件及各种因素对该方法测定结果的影响．