Shang J. Yao

The Interference Of Ascorbate And Urea In Low-potential Electrochemical Glucose Sensing

Ascorbate and urea are present in body fluid at relatively high concentration and could cause interference during glucose sensing. The potential interference of these two substances was investigated using a small planar electrode in the low potential region of the cyclic voltammogram. that is, -0.750 V to +0.450 V versus Ag/AgCI. The ascorbate signal near -0.750 V was found to increase linearly as its concentration was increased from 1 to 10 mg/dl. The effect of changes in concentration of urea in the 20 to 60 mg/dl range did not cause an obvious variation in glucose current at -0.750 V. Regularities in signal variations at -0.750 V and in other regions of the voltammogram (for example at -0.530 V) were observed. Using these regularities, a scheme for signal processing was developed to compensate for the effect of the interferences.

An enzyme electrode for the determination of l-glutamic acid

Abstract The feasibility of determining L-glutamic acid concentration using a potentiometric technique was explored. A S everinghaus -type pCO2 electrode measured carbon dioxide released from the substrate with L-glutamic decarboxylase. The enzyme was suspended in o.i M phosphate buffer (ph 5.0) at 37 °C. A linear relationship was observed between the electrode potential and the logarithm of L-glutamic acid concentration, The average relative error was 1.7 % for substrate concentrations of 0.4–10.0 mg % and 6 % for the extended range of 0.2–10 mg %. A soluble L-glutamic decarboxylase was insolubilized by glutaraldehyde cross-linking. The insolubilization yield was 5.5 % by weight and the activity of the insolubilized enzyme 1.4 % compared to the original enzyme. The insoluble enzyme was immobilized with cellulose or silicone adhesive. A semi-quantitative electrode response to added substrate was observed. The same technique as reported could be applied to the determination of other L-amino acids using respective decarboxylases.

Enzymatic-potentiometric determination of oxalic acid

Abstract A method utilizing oxalate decarboxylase and potentiometry is described for the determination of oxalic acid. The oxalic acid was enzymatically decomposed to form formic acid and carbon dioxide. The released CO 2 was measured potentiometrically using a CO 2 electrode. A nernstian relationship between the voltage output of the CO 2 sensor and the concentration of oxalic acid, in the physiological range, 0.3–1.0 mg per 100 cm 3 , has been observed.

Zeolitic Ammonium Ion Exchange for Portable Hemodialysis Dialysate Regeneration

&NA; Ammonia removal from a recirculating dialysate stream is a major challenge in developing a truly portable, regenerable hemodialysis system. Three zeolites, type F, type W, and clinoptilolite, were found to have good ammonia ion exchange capacity with linear equilibrium ion exchange coefficients of 0.908, 0.488, and 0.075 L/g, respectively. The linear equilibrium ion exchange coefficient relates dialysate ammonia concentration (μmol/L) to the amount of ammonia absorbed by zeolite (μmol/g) at equilibrium. Ammonia uptake by zeolite powders was fast, with equilibrium reached within 15 sec. Zeolite ammonia ion exchange and regeneration through multiple cycles was studied using an ion exchange column containing clinoptilolite pellets. Zeolite ion exchange capability was regenerated by flushing the column with 2 mol/L sodium chloride after an ion exchange run. The column maintained ammonia ion exchange capacity through six ion exchange/regeneration cycles, demonstrating multiple dialysis use possibilities. Atomic absorption spectroscopy of the column effluent showed no detectible (<1 part per million) Si or Al leached from the zeolite. ASAIO Journal 1995; 41:221‐226.

A micro carbon electrode for nitric oxide monitoring.

A nitric oxide (NO) probe, consisting of a micro carbon fiber working electrode, 10 microns diameter, a platinum counter electrode, and a silver/silver chloride (Ag/AgCl) reference electrode, has been developed. The carbon fiber working electrode is covered with a Nafion cation exchange membrane. Using differential pulse voltammetry (DPV), we found the NO to N2O reduction current peak at approximately -1.35 V versus Ag/AgCl. This has been reported by others. The DPV current outputs are linearly related to dissolved NO concentrations [NO] in the 2-10 microM range. Catecholamines were found not to interfere with the reduction signal. The Nafion membrane also prevents interference by NO2-, NO3-, and amino acids at normal physiologic pH (pH 7.4). The effects of O2 are accounted for through sampling and subtracting background currents from the peak current. To increase sensitivity and shorten response time, a method of integrated pulse amperometry (IPA) was used for the study. The IPA charge outputs (delta C) are linear to the dissolved [NO] in the 50-350 nM range. The carbon fiber electrode has the potential of being miniaturized to a smaller electrode, allowing detection of NO released from the subendothelial space.

Controlled-potential controlled-current electrolysis: in vitro and in vivo electrolysis of urea

Abstract A controlled-potential, controlled-current (c.p.c.c.) method for electrolysis has been developed. Electrolysis is performed under controlled oxidative and controlled reductive currents within preset upper and lower bound potentials. The c.p.c.c. approach accomplishes both electrolysis and electrode regeneration concurrently. Compared with the existing galvanostatic and/or controlled potential electrolysis, the present approach demonstrates a greater selectivity for the electroactive species. The approach has been applied to direct electrolysis of urea in physiologic solutions and in recirculated canine hemodialysate. No undesirable, harmful, or toxic products have been found. The Pt-black electrodes, rejuvenated during the electrolysis, were found to perform as well in a standard test as they had prior to electrolysis of the hemodialysate. In view of its selective and regenerative nature, c.p.c.c. electrolysis is thought to be suitable for urea removal in a closed-loop, regenerative hemodialysis system. It is also most likely adapatable to other electrolyses of clinical substances.

345 - Electrochemical removal of urea from physiological buffer as the basis for a regenerative dialysis system☆

Abstract The electrochemical removal of urea coupled with charcoal adsorption can be used to remove the wastes from spent dialysis fluid. This regeneration of dialysis fluid in a closed-loop system would permit the utilization of small volumes of fluid and provide the basis for a portable hemodialysis apparatus. The studies presented involve the direct electrochemical oxidation of urea from physiological buffer. Various electrolysis parameters were studied to improve the urea removal rate. Preliminary studies of reaction products indicated that urea is converted into nontoxic products which would be easily removed by other body systems ( e.g. respiration). The addition of several other compounds known to be removed by dialysis caused no decrease in the electrochemical removal of urea.

De-ureation by electrochemical oxidation

Abstract A study of the anodic oxidation of urea on a Pt-black electrode in K rebs -R inger bicarbonate buffer in the presence of glucose was performed. Changes in urea and glucose concentration, pH and anode half-cell potential were measured. At a current density of 0.5 mA cm −2 and an electrode area of 50 cm 2 , 4×10 −4 mole urea was oxidized in a 15 h run. NH 4 + , NO − 3 , and NO − 2 were not found as products of the oxidation. Calculations of coulombic utilization during the oxidation process were compatible with a 6-electron process. N 2 , CO 2 , and H 2 O were the most likely products. The feasibility of developing an electrochemical de-ureator, utilizing electrocatalysts, electricity and air or O 2 for urea removal by a portable artificial kidney was explored.

Platinized-titanium electrodes for urea oxidation Part II. Concentric spiral coil geometry

Abstract Highly active urea electro-oxidation catalysts were prepared by electrodeposition of Pt onto Ti in a novel, concentric spiral coil geometry. The concentric spiral coil geometry can be used directly in construction of electrochemical reactors. The Pt deposition from chloroplatinic acid required about 1.5 times the stoichiometric charge. Projection of urea conversion activity from cyclic voltammetry measurements to a clinical-scale, portable hemodialysis system indicates that approximately 10 g of Pt will be required for the clinical-scale system. The specific urea conversion activity, as measured by cyclic voltammetry, is linearly related to the specific Pt surface area of the deposition. The depositional growth morphology is found to be self-similar, with a fractal dimension that lies somewhere between uniform deposition and hemispherical growth.

A nitric oxide sensor using reduction current.

Nitric oxide (NO) has a wide range of biologic activity. Methods commonly used for the detection of biologically derived NO are indirect and measure only the amount of NO released during an interval of time. An electrochemical method available is capable of being direct and continuous but is subject to interference. The recent explosion of scientific research into NO activity requires better methods of NO detection. This article reports a new NO electrochemical sensing method and sensor design. The tip of the sensor is covered with a hydrophobic membrane and contains an internal electrolyte. Platinum is used for the working and counter electrodes and silver/silver bromide (Ag/AgBr) for the reference electrode. The components of the internal electrolyte are potassium bromide and sulfuric acid. The NO that diffuses to the working electrode is first oxidized to NO+; the NO+ is reduced to NO; and the reduction current is determined. An integrated pulsed amperometric method is used to achieve the redox of NO and the measurement and integration of the reduction current. The results show that the NO sensor is sensitive and has a rapid response and less interference.