Indirect determination of formaldehyde by alternating-current voltammetry at a hanging mercury drop in the presence of oxygen

An alternating-current voltammetric procedure has been developed for the indirect determination of formaldehyde as its hydrazone at a stationary hanging mercury drop over the formaldehyde concentration range from 0.2 to 15 mg/L in a buffer solution of pH 5.6 ± 0.4 without removing dissolved oxygen. An EKOTEST-VA miniature voltammetric analyzer connected to a computer was used. The detection limit for formaldehyde in the proposed procedure was 0.2 mg/L.     

Differential Pulse Polarographic Determination of Gallium and Niobium in Samples After Preconcentration of Their Quinolin-8-Olate Complexes on Microcrystalline Naphthalene

Abstract

Gallium and niobium react with quinolin-8-ol to form water insoluble complexes which are quantitatively adsorbed on microcrystalline naphthalene from the large volume of their aqueous solutions in the pH range of 3.5 - 8.2 and 6.2 - 9.4, respectively. After filtration, the metal complexes were desorbed with 10 ml of HCl (1M for Ga and 11 M for Nb) and determined by using a differential pulse polarograph (DPP). The dissolved oxygen is removed by adding a few milliliters of 4% NaBH₄ solution in the case of gallium. The detection limits are 0.04 ppm for gallium and 0.05 ppm for niobium at the minimum instrumental settings (signal to noise ratio = 2). The linearities are maintained in the concentration range 0.1 - 5.0 ppm for gallium and 0.4 - 6.0 ppm for niobium with correlation factors of 0.9997 and 0.9996 and relative standard deviations of 0.81 and 0.95%, respectively.

Characterization of the electroactive process included an examination of the degree of reversibility. Various parameters such as the effect of pH volume of aqueous phase, reagent and naphthalene concentrations and the interference of a large number of anions and cations on the estimation of these elements were studied in detail. The method is found to be highly selective, fairly sensitive, rapid, simple and economical. It has been applied for the trace determination of gallium and niobium in various standard alloys and may be applied safely for the analyses of complex materials like environmental samples and ores.

     

N-Methylethylxanthocarbamate as an Analytical Reagent: Differential Pulse Polarographic Determination of Cadmium in Standard Alloys, Biological and Environmental Samples after Adsorption of its Complex on Microcrystalline Naphthalene

N-methylethylxanthocarbamate has been used as an analytical reagent for the determination of trace amounts of cadmium in standard alloys, biological, and environmental samples. The reagent has been found to form a water insoluble complex with cadmium. It is quantitatively adsorbed over microcrystalline naphthalene in the pH range 2.5 to 12.0. The metal complex is desorbed with HCl and cadmium determined with a differential pulse polarograph. The detection limit is 0.05 ppm (signal-to-noise ratio = 2) and the linearity is maintained in the concentration range 0.2–25 g/ml, with correlation coefficient of 0.9995 and a relative standard deviation of ±0.81%. Characterization of the electroactive process includes an examination of the degree of reversibility. Various parameters, such as the effect of pH, reagent concentration, amount of naphthalene, volume of aqueous phase, and the interference of a large number of metal ions on the determination of cadmium, have been studied in detail to optimize the conditions for its determination in various complex materials.     

阴极溶出催化极谱法测定微量硒

本文提出将溶出伏安法和极谱催化法结合起来,用溶出催化波来测定微量硒;考察了各种试验条件及其它离子对分析结果的影响,并对实样进行了分析测定。用国产883型笔录式极谱仪,配用旋转玻碳电极测定硒,电解富集3-5分钟,可定量测定浓度在4×10^-9-1×10^-7M 范围内的硒;富集20-30分钟,硒的检出下限为7×10^-10M。测定时不必除氧。在测定硒的基础上,用玻碳电极和大汞电极相配合,对硒的溶出催化电极过程进行了研究,探讨了此过程中各步反应的机理。     

Polarographic determination of aluminium with alizarin

The polarographic determination of aluminium as its complex with alizarin in the pH range 9.2-10.1, with the cathode ray polarograph, is described. A solvent extraction procedure is used to eliminate interferences from many other metals.     

Determination of Cr(III) and Cr(VI) in industrial and environmental liquid samples by EDXRF method

A rapid, sensitive and selective procedure for determination of Cr(III) and Cr(VI) in environmental and industrial liquid samples via preconcentration with ammonium pyrrolidine dithiocarbamate (APDC) and determination by means of the EDXRF was described. The effect of pH in the range of 3-11 on the recovery of Cr(III) and Cr(VI) has been investigated separately and in combination of these two species. The influence of organic matter, carbonate species and elements V, Mn and Fe on the recovery of each chromium specie (separately/in combination) over whole pH range was also tested in order to simulate condition occurring in natural waters that usually contain certain amount of dissolved organic matter and carbonate ions. Cr(VI) and Cr(III) have shown different behaviors in reaction with APDC at different pH ranges and therefore it is possible to separate those two species. It was found that Cr(VI) creates complex with APDC only in the pH range from 3 to 5 with quantitative recovery (app. 98%) at pH 3, but there was no recovery of Cr(III) at that pH. On the contrary, in pH range from 6 to 11, reaction with Cr(III) and APDC reviled that the only reaction product is Cr(OH)₃ instead of the expected Cr(III)-APDC complex. All reaction products were characterized by IR spectroscopy.     

Measurement of Dissolved Oxygen in Biological Fluids by Using a Modified Carbon Paste Electrode

A modified carbon paste electrode was constructed for the determination of dissolved oxygen using diamino‐o‐benzoquinone (DABQ) as the modifier. The electrochemical behavior of the electrode in citrate buffer (pH 2.0) was studied. In the presence of dissolved oxygen (DO) both cathodic and anodic peak currents decreased, indicating a chemical reaction between modifier and O₂. The decrease in peak current was linearly proportional to the amount of dissolved oxygen in the concentration range of 252–1260 μM of DO. The electrode was utilized in the determination of DO in urine samples. The relative error and RSD of the method were 1.6% and 4.1%, respectively. The electrode was applied more than two months for the determination of DO without any significant divergence in its voltammetric response.     

Determination of reducing sugars with a 2,4-dinitrophenolate-selective membrane electrode

A 2,4-dinitrophenolate-selective liquid-membrane electrode based on tetrapentylammonium dinitrophenolate dissolved in 2-nitrotoluene is described. The electrode exhibits rapid and near- Nernstian response to the activity of 2,4-dinitrophenolate anions in the range 3×10^?5 ?1×10^?2 M. The response is unaffected by pH in the range 7.5–12.5. The electrode has been successfully applied to the kinetic potentiometric determination of fructose, glucose and galactose at 60°C and of fructose in the presence of glucose and galactose at 30°C. The electrode can be used for the potentiometric determination of glucose and fructose after completion of the reaction with excess of 2,4-dinitrophenolate ions and of sucrose after acid hydrolysis. Mixtures of glucose, fructose and sucrose in aqueous solutions or honey samples can be determined by the proposed procedures with an average error of about 2%.     

Green Synthesis of Silver Nanoparticles Using Ionic Liquid and Application for the Detection of Dissolved Oxygen

The electrochemical synthesis of silver nanoparticles (nano‐Ag) has been successfully carried out on glassy carbon electrode (GCE) and indium tin oxide electrode (ITO) using 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMT) as green electrolytes. Further the electrodeposited nano‐Ag modified ITO electrode has been examined using atomic force microscopy (AFM), and X‐ray diffraction studies (XRD). The electrodeposited Ag nanoparticles on ITO were found in the size range of 5 to 35 nm. The nano‐Ag film modified GCE was further coated with nafion (Nf) and BMT (1 : 1 ratio) mixture and found to be stable in BMT and in pH 7 phosphate buffer solution (PBS). The nano‐Ag/BMT‐Nf film modified GCE successfully applied for the oxygen reduction reaction in neutral pH (pH 7.0 PBS). The proposed film modified GCE successfully reduces the over potential and show well defined reduction peaks for the detection of dissolved oxygen using cyclic voltammetry (CV) and rotating disc voltammetry (RDE). The film also applied for the detection of dissolved oxygen using electrochemical impedance spectroscopic studies (EIS).     

电化学发光淬灭法测定SOD

在硼酸缓冲溶液（pH6．7）中性介质中,O2和H2O2均对鲁米诺的电化学发光（ECL）有敏化作用,而超氧化物歧化酶（SOD）对此敏化的电化学发光具有淬灭作用,SOD的浓度与两种发光体系的ECL光强成线性关系,可用于SOD的测定,为SOD的测定提供了一种灵敏、可靠的测定方法。     

Determination of germanium by potentiometric stripping analysis and adsorption potentiometric stripping analysis

Potentiometric stripping analysis was applied to determination of germanium(IV) in 0.2M NH₃-NH₄Cl (pH 8.4) buffer solution at −1.8 V (vs. Ag/AgCl), with dissolved oxygen or Hg(II) as oxidant. The sensitivity was 8.5 × 10⁻⁹M in the presence of 2.0 × 10⁻⁵M Hg(II) with plating for 15 min after deaeration for 20 min. Cyclic voltammetry revealed that GE(IV) å Ge at the surface of the mercury-film electrode in a one-step irreversible reduction reaction, and the Ge at the electrode was oxidized by dissolved oxygen in the solution. The presence of complexing agents such as Alizarin Red (ARS), which forms a Ge(IV) complex adsorbed at the electrode, improved the sensitivity by one order of magnitude. The presence of adsorption was revealed by the temperature coefficient, the electrocapillary curve and cyclic voltammetry. Ge-containing samples were analysed by the proposed methods and agreement with the results obtained by other methods was excellent.     

Determination of lead, cadmium and zinc ions in large excess of indium ion using the alternating current polarograph

Lead, cadmium or zinc ions in the presence of a large excess of indium ion can be determined, without removal of excess indium and dissolved oxygen, by means of the alternating current polarograph in supporting electrolytes such as nitric acid or phosphoric acid.     

Measurement of the peroxidation of Brji-35 in aqueous solution by hemin and horseradish peroxidase catalyzed fluorogenic reaction

The non-ionic surfactant Brij-35 can easily be oxidized in solution by dissolved oxygen upon light radiation during its storage. Various factors, such as light radiation, temperature, pH, ionic strength as well as dissolved oxygen influencing the stability of Brij-35 were studied. The results showed that light radiation is the most important factor inducing the oxidation by the dissolved oxygen. The oxidized product was confirmed, indirectly, to be the peroxide of Brij-35 based on a number of evidences. The extent of the oxidation can be traced by a peroxidase or hemin catalyzed fluorogenic reaction with p-hydroxyphenylacetic acid as a substrate. The concentration of the peroxide in a Brij-35 solution (0.8%, w/v) stored at room temperature for a month is in the range of 9 × 10^–5 mol/L.     

血红蛋白过氧化物模拟酶胶束催化显色体系

在胶束Tween80介质中，研究了以血红蛋白（hemoglobin,Hb)作为过氧化物模拟酶、隐性亮绿（recessive brilliant green,RGB)为氢供体底物、溶解氧为受氢体的酶催化反应特性。在pH5.64(NH4)2HPO4-KH2PO4缓冲溶液中，利用模拟酶对溶解氧作为受氢体催化RBG氧化生成亮绿（brilliant green,BG)而拟定了测定Hb含量的新方法。讨论了胶束介质对酶体系催化反应的影响及酶催化反应的可能机理。     

Polarographic Determination of Glycyrrhizic Acid Based on Double Enhancement Action of Surfactant and Dissolved Oxygen

ABSTRACT

A method for the determination of glycyrrhizic acid (GA) is described based on polarographic current of GA enhanced doubly by both cation surfactant (cetyl trimethyl ammonium bromide (CTMAB)), and dissolved oxygen (including oxygen-derived species). The doubly enhanced current of GA includes two additional currents. One is the increased reduction current of adsorbed GA induced by CTMAB. The other is the catalytic current of GA caused by the dissolved oxygen molecule and its derived species. In 0.1 M NaAc-Hac (pH4.7±0.1) ～ 1x10^?5 M CTMAB supporting electrolyte without deoxygenation, the enhanced current of GA is linearly proportional to its concentration in the range of 4x10^?7 M ～ 4.0x10^?6 M. The detection limit is 1.8x10^?7 M. The double enhanced current of GA in sensitivity is about 15 times higher than its reduction wave in the same acetate buffer solution.     

Glucose Biosensor Based on Multi‐Walled Carbon Nanotube Modified Glassy Carbon Electrode

An amperometric glucose biosensor based on multi‐walled carbon nanotube (MWCNT) modified glassy carbon electrode has been developed. MWCNT‐modified glassy carbon electrode was obtained by casting the electrode surface with multi‐walled carbon nanotube materials. Glucose oxidase was co‐immobilized on the MWCNT‐modified glassy carbon surface by electrochemical deposition of poly(o‐phenylenediamine) film. Enhanced catalytic electroreduction behavior of oxygen at MWCNT‐modified electrode surface was observed at a potential of ?0.40 V (vs. Ag|AgCl) in neutral medium. The steady‐state amperometric response to glucose was determined at a selected potential of ?0.30 V by means of the reduction of dissolved oxygen consumed by the enzymatic reaction. Common interferents such as ascorbic acid, 4‐acetamidophenol, and uric acid did not interfere in the glucose determination. The linear range for glucose determination extended to 2.0 mM and the detection limit was estimated to be about 0.03 mM.     

A compleximetric method for the determination of dissolved oxygen in water

A new method is proposed for the determination of dissolved oxygen in water. The iron(III) formed from FES at pH 7.5 is titrated with EDTA solution in presence of salicylic acid indicator after adjustment of the pH to about 2.4 The method is slightly less precise than the Winkler method for pure waters but more accurate for polluted waters; it is simple and convenient for field use.     

On the reduction of oxygen in aqueous solution by electrolytically precipitated cadmium

The reduction of oxygen in aqueous solution by electrolytically precipitated cadmium, used in a reductor column, has been studied in two ways. First, by analysis of the effluent for the hydrogen peroxide formed as a reaction intermediate, the conditions for quantitative reduction have been found. Attention is called to the fact that an effluent free from hydrogen peroxide also implies quantitative reduction of all dissolved oxygen. The practical consequences are pointed out. A comparison is also made with some other reductors. Secondly, the oxidation of electrolytically precipitated cadmium by hydrogen ion is strongly inhibited, so at pH 7 it is possible to determine oxygen as the equivalent amount of cadmium ion produced in the reductor column. The conditions of quantitative reduction of oxygen are determined and found to be in agreement with those obtained by the first method. From the results the solubility of oxygen in water in equilibrium with air is estimated and found to agree with a published result considered as reliable. An outline is given of a method for determination of oxygen in aqueous solution by measurement of the amount of cadmium ions produced.     

Measurement of the peroxidation of Brji-35 in aqueous solution by hemin and horseradish peroxidase catalyzed fluorogenic reaction

The non-ionic surfactant Brij-35 can easily be oxidized in solution by dissolved oxygen upon light radiation during its storage. Various factors, such as light radiation, temperature, pH, ionic strength as well as dissolved oxygen influencing the stability of Brij-35 were studied. The results showed that light radiation is the most important factor inducing the oxidation by the dissolved oxygen. The oxidized product was confirmed, indirectly, to be the peroxide of Brij-35 based on a number of evidences. The extent of the oxidation can be traced by a peroxidase or hemin catalyzed fluorogenic reaction with p-hydroxyphenylacetic acid as a substrate. The concentration of the peroxide in a Brij-35 solution (0.8%, w/v) stored at room temperature for a month is in the range of 9 × 10^–5 mol/L. Received: 8 February 1999 / Revised: 13 April 1999 / Accepted: 17 April 1999     

An optical glucose biosensor based on glucose oxidase immobilized on a swim bladder membrane

An optical glucose biosensor using a swim bladder membrane as an enzyme immobilization platform and an oxygen-sensitive membrane as an optical oxygen transducer has been developed. During the enzymatic reaction, glucose is oxidized by glucose oxidase with a concomitant consumption of dissolved oxygen resulting in an increase in the fluorescence intensity of the optical oxygen transducer. The fluorescence intensity is directly related to the glucose concentration. The effects of pH, temperature, buffer concentration, and selectivity have been studied in detail. The immobilized enzyme retained 80% of its initial activity after being kept for more than 10 months at 4°C. The glucose biosensor has been successfully applied to the determination of glucose content in human blood serum and urine samples. Martin M.F. Choi was on sabbatical leave at The University of North Carolina at Chapel Hill from July 2004 to July 2005.