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.     

Microdetermination of alkaloids in organic solvents by potentiometric titration

A small-intefacial voltaic cell (antimony scratch) is shown to be satisfactory for end-point detection in titrations of various alkaloids and other basic drugs and their salts in ethanol, chloroform or dibutyl ether media with picric acid in the same medium. Small (0.4–4 mg) amounts can be determined. This method has the advantages of being simple and rapid with sharp end-points. The recoveries were 96.52-100.8% for the determinations of 19 drugs and their salts. The relative error was ±5% for five pharmaceutical tablets and injections.     

Indirect potentiometric monitoring of proteins with a copper electrode

Preliminary results are given for the monitoring of proteins by indirect potentiometry with the Cu²⁺/Cu couple in a flow system. Electrochemical cleaning of the electrode, before measurement of the potential in the presence of proteins, allows reproducible determinations of proteins at the micromolar level. The effects of pH and chloride on the measured potentials are investigated.     

Coal solubilization by enhanced enzyme activity in organic solvents

Applied Biochemistry and Biotechnology - Both oxidative and reductive enzymes can be utilized to enhance coal solubilization in aqueous and organic media. Aerobic solubilization was carried out...     

A new potentiometric gas sensor-the air-gap electrode

The concept and construction of a newly developed gas sensor, the air-gap electrode, is described. The hydrophobic gas-permeable membrane generally employed in gas electrodes is replaced by an air gap which separates the electrolyte layer from the sample solution. By avoiding the membrane construction and utilizing a very thin layer of electrolyte at the surface of the indicator electrode, a very high speed of response is obtained. Furthermore, the life time of the sensor is substantially increased, as the electrode does not come into direct physical contact with the sample solutions; thus there is no interference from surfactants, particulate matter or organic solvents. The electrolyte layer can be easily renewed or even changed according to the requirements of a particular analysis, so that the same electrode can be used for measurements of a variety of gases. Two different techniques of applying the air-gap electrode are described. The airgap electrode was used to determine the carbon dioxide and ammonia contents of a series of samples, using sample volumes from 50–150 μl to several ml. The electrode was also used to determine the ammonium ion content in serum and plasma samples, yielding highly satisfactory results. The speed of response was of the order of 1–3 min. Some potential applications of the sensor are mentioned.     

A method for detecting water in organic solvents

The potent dehydrating ability of difluoro(aryl)-lambda (3)-iodanes is exploited to develop a convenient (19)F-NMR-based aquametry method that is more sensitive than coulometric Karl Fischer titration. The key difluoro(aryl)-lambda (3)-iodane reagents are synthesized readily from commercially available and inexpensive precursors.     

A specific enzyme electrode for urea

A truly specific, simple enzyme electrode is described for the assay of urea in blood serum. The sensor used is the newly developed air-gap electrode of R??i?ka and Hansen, and has advantages of speed of response and specificity over earlier enzyme electrodes for urea. Potassium, sodium and ammonium ions and other organic and inorganic species present in blood do not interfere. Linear curves are obtained from 2 · 10^-2M to 1 · 10^-4M urea with slopes close to Nernstian (about 0.90 pH/decade). Urea in blood was assayed with an accuracy of 2.2% and a precision of 2.0% with immobilized urease; only 3–5 min is required per assay. The electrode was used for a month and almost 500 assays with excellent results. Since the sensor never touches the sample solution, problems caused by blood components which block membrane pores are avoided.     

A specific enzyme electrode for L-phenylalanine

A specific enzyme electrode procedure is described for the rapid assay of L-phenyl- alanine. The enzyme L-phenylalanine ammonia lyase is used, which cleaves L-phenyl-alanine to ammonia. The ammonia liberated is measured with an air-gap electrode. The procedure is specific; L-tyrosine and other amino acids do not interfere, nor do Na⁺ or K⁺ ions. As little as 5 · 10^-5 M L-phenylalanine can be determined.     

A silver electrode in the potentiometric titration of thiols

A silver wire immersed in a thiol solution gives a potential responsive to the thiol concentration, and is a sensitive indicator electrode in the potentiometric titration of thiols with mercury(II) chloride, p-chloromercuryphenyl sulphonate, and silver nitrate at pH 4.5-9.5, 7-9.5 and 9.5 respectively. Titrations of simple thiols such as cysteine or a protein such as albumin are equally successful, but the potential break was smaller for the protein. The end-point could be determined within an increment of titrant equal to 5 nmole of thiol. An inert atmosphere is needed for titration at pH 7.     

Screen-printed electrode based on AChE for the detection of pesticides in presence of organic solvents

A screen-printed biosensor for the detection of pesticides in water miscible organic solvents is described based on the use of p-aminophenyl acetate as acetylcholinesterase substrate. The oxidation of p-aminophenol, product of the enzymatic reaction was monitored at 100 mV vs. Ag/AgCl screen-printed reference electrode. Miscible organic solvents as ethanol and acetonitrile were tested. The acetylcholinesterase (AChE) was immobilised on a screen-printed electrode surface by entrapment in a PVA-SbQ polymer and the catalytic activity of immobilised AChE was studied in the presence of different percentages of organic solvents in buffer solution. The sensor shows good characteristics when experiments were performed in concentrations of organic solvents below 10%. No significant differences were observed when working with 1 and 5% acetonitrile in the reaction media. Detection limits as low as 1.91x10(-8) M paraoxon and 1.24x10(-9) M chlorpyrifos ethyl oxon were obtained when experiments are carried out in 5% acetonitrile.     

A ferrocene-modified platinum electrode as a potentiometric sensor for l-ascorbic acid

A half-oxidized platinum electrode modified with a monolayer of ferrocene is proposed as a potentiometric sensor for l-ascorbic acid in an aqueous glycine buffer pH 2.2. The ferrocene was covalently attached to the surface by a silane carbon chain. The potentials of 15 electrodes were measured and a slope of (50 ± 8.8) mV per decade change in concentration of ascorbic acid was obtained over the concentration range 10^?3-10^?6 M. Recovery experiments with pure l-ascorbic acid solutions showed a relative standard deviation of 1.9%, in the analysis of fresh orange juice, the relative standard deviation was 6.1%.     

A clean and rapid liquid chromatographic technique for sulfamethazine monitoring in pork tissues without using organic solvents

A rapid method for the isolation and high-performance liquid chromatographic (HPLC) determination of sulfamethazine (SMZ) in pork tissues (kidney, liver, and muscle) without using organic solvents is developed. The isolation is performed by homogenization with an acid solution using an ultrasonic-homogenizer, followed by centrifugation. The HPLC analyses are performed using a reversed-phase C(4) column (150- x 4.6-mm i.d.), a mobile phase of 0.02 mol/L citric acid solution, and a photodiode array detector. The resulting HPLC chromatograms are free from interferences for determination and identification. The proposed technique is shown to be linear (r > 0.99) over the concentration range 0.1-2.0 microg/g for all pork tissues. Average recoveries of SMZ (spiked 0.1-2.0 microg/g) range from 87.6% to 90.2%, with inter- and intra-assay variabilities of less than 4%. The total time required for the analysis of one sample and limit of quantitation is less than 20 min and 0.09 microg/g, respectively.     

A test method for determining water in organic solvents

A test procedure is developed for determining water in acetone, dioxane, isobutanol, ethanol, petroleum ether, and ethyl acetate in the ranges 0.5–12; 0.5–10; 0.5–8; 0.5–6, and 0.5–4 vol %, respectively. Determination is based on the measurement of the acidity of a solution obtained upon adding citric acid or sodium hydrogen sulfate to organic solvents using an indicator test strip containing Congo red. The relative standard deviation of the results of analysis is 0.05–0.1; the duration of analysis is about 30 min.     

Biosensors based on a light-addressable potentiometric sensor (LAPS) for analysis in both aqueous solutions and organic solvents

Characteristics of a light-addressable potentiometric sensor (LAPS) based on silicon with Ta₂O₅ dielectric are reported. The pH sensitivity obtained is 45 mV/pH unit in the pH range from 4.01 to 7.5 (for measurements conducted in citrate buffer solutions) and 55 mV/pH unit over the pH range from 7.5 to 8.9 (for measurements conducted in Tris-HCl buffer solutions). The kinetic characteristics (K _m ³ V _m ⁵ pH-profile) of different enzymes, i.e., glucose oxidase, α-chymotrypsin, butyrylcholin esterase, and urease, have been measured under homogeneous conditions. The values of the Michaelis constant obtained are very close to analogous data described in the literature. Biosensors were prepared by immobilization of the enzymes on a pH-sensitive matrix. Two methods of immobilization were used: incorporation in to a hydrophilic matrix of bovine serum albumin (BSA) and incorporation into a hydrophobic matrix of modified polyethylenimine (PEl). It is demonstrated that LAPS can be used for recording the enzymatic reactions in organic media (mixture of the solvents).     

A coated-metal enzyme electrode for urea determinations

A potentiometric enzyme electrode is reported in which an enzyme immobilized in polyvinyl chloride is used to coat an antimony metal electrode to detect changes in pH when the electrode is immersed in a solution of the enzyme substrat. As an example, urea is determined in solution by using immobilized urease on an antimony electrode, giving a linear concentration range of 5.0 × 10^-4–1.0 × 10^-2 M urea with a slope of 44 mV per decade change in urea concentration. The response slope is stable for about 1 week, with response times in the range 1–2 min, but with absolute potential changes occurring from day to day.     

Microfluidic devices with disposable enzyme electrode for electrochemical monitoring of glucose concentrations

This article describes the fabrication of tube-like microchannels made of UV curable polymer on a glass substrate and the device assembling with a disposable enzyme-working electrode for high-sensitivity electrochemical detection. While both reference and counter electrodes are patterned on the surface of the glass substrate, the working electrode is flipped on the top of the channel with an open access, providing a face-to-face probing configuration. When the enzyme electrode is contaminated or degraded, it can be easily replaced by a new one, keeping the main body of the device and the detection schema unchanged. Using glucose oxidase-coated gold electrodes, we were able to determine a linear amperometry response to the glucose concentrations in the range of 2-16 mM. By replacing the as-prepared working electrode by the one after thermal treatments, we showed a much more degraded enzyme electrode activity, enabling efficient determination of the electrode quality as well as the whole process optimization.     

以锑电极作参比电极测定废水中硫化物

提出了以锑电极作为参比电极与Ag2 S电极组成无液接测量电池测定废水中硫化物的新方法。并研究了电极的性能 ,测定条件及干扰物质的影响。方法的线性范围 1 .0× 1 0 - 2 mol/L～ 5 .0× 1 0 - 7mol/L[S2 - ],回收率为 99%～1 0 3%