Reduction of oxygen at a NaX-Ag composite electrode and its application to the determination of oxygen in aqueous media

A composite mixture Ag-NaX zeolite (silver concentration 16.7% w/w) is synthesized usingim-pregnation and thermal decomposition. For silver impregnation, a solution of an Ag acetylacetonate complex in acetone was used. Despite the quantity of silver applied was substantially less than it would be necessary to fill the inner pore space in the zeolite completely, some part of silver formed nanocrystallites and nanoparticles giving rise to a novel composite material. The composite powder was uniformed with soot (10% w/w) and applied onto a mirror-smooth graphite surface used as an electrode matrix. The reduction of oxygen on such a surface proceeded with activity comparable to that observed on the most active planes of the silver single crystal, Ag(100).     

Improvement of the silver/silver chloride reference electrode and its application to pH measurement

When a silver/silver chloride (Ag AgCl ) reference electrode was used continuously in a low conductivity solution or reductive solution, it was often observed that stability of the liquid junction potential was lost. This phenomenon was remarkable with a Ag AgCl reference electrode compared to a calomel reference electrode. We found that 340 mg l(-1) of silver was dissolved in 3 M potassium chloride (KCl) internal solution as silver complex ions (AgCl(-(x-1))(x)) for x = 2 or 3. However, only 1.93 mg l(-1) of silver chloride (AgCl) can theoretically be dissolved in water. The complex ion that effused into the sample solution through the liquid junction clogged the liquid junction (e.g. porous ceramic) as AgCl, or as metallic silver (Ag) in reducing solution. Therefore, the constant effusion of KCl internal solution was inhibited, and the liquid junction potential became unstable or fluctuating. A new reference electrode was developed, which can eliminate AgCl(-(x-1))(x) in 3 M KCl internal solution by the use of chelating resins. A combination of this reference electrode with a pH electrode made long-term stable pH measurements possible.     

An improved air-gap electrode and its application to the measurement of carbonate in interstitial water

Summary The air-gap gas sensing electrode according to Rika is improved in several aspects. The reliability was increased by the use of a combined glass-reference electrode. A new way of sample introduction gave a better accuracy in practice. The electrode is used to determine carbonate concentrations in the range of 5 · 10^–2–5 · 10^–4M with an accuracy of 2–9%. The electrode is in use in the analysis of environmental carbonate.

---

Verbesserte Luftspaltelektrode und ihre Anwendung zur Carbonatbestimmung in Porenwasser

Zusammenfassung Die Luftspaltelektrode nach Rika wurde in einigen Punkten verbessert. Ihre Zuverlässigkeit wurde durch Anwendung einer Einstabmeßkette erhöht; ein neues System der Probezugabe bietet eine bessere Genauigkeit in der Praxis. Die Elektrode wurde zur Messung von Carbonatkonzentrationen im Betrieb von 5 · 10^–2–5 · 10^–4 M eingesetzt, wobei die Genauigkeit 2–9% betrug. Sie wird zur Umweltanalyse von Carbonat angewendet.

     

Micro-Winkler titration method for dissolved oxygen concentration measurement

In this report a gravimetric micro-Winkler titration method for determination of dissolved oxygen concentration in water is presented. Mathematical model of the method taking into account all influence factors is derived and an uncertainty analysis is carried out to determine the uncertainty contributions of all influence factors. The method is highly accurate: the relative expanded uncertainties (k = 2) are around 1% in the case of small (9-10 g) water samples. The uncertainty analysis carried out in characterizing the uncertainty of the method is the most comprehensive published for a micro-Winkler method, resulting in experimentally obtained estimates for all uncertainty sources of practical significance (around 20 uncertainty sources altogether).     

Thin layer flow cell with a rotating disk electrode

A channel-type electrochemical flow cell with a rotating disk electrode has been constructed and characterized. The work shows that the effect of rotation is to enhance the rate of mass transport. At rotation speeds higher than 900 rpm the response becomes independent of the flow rate and channel thickness. As a result, low flow rates can be used without sacrificing the sensitivity. Analytical advantages are demonstrated using liquid chromatography, stripping analysis, stopped rotation voltammetry and flow injection analysis.     

An electrochemical thermometer: voltammetric measurement of temperature and its application to amperometric gas sensing

We report a temperature sensing system incorporated into an amperometric oxygen sensor. In the first part of this work, we introduce temperature sensing systems based upon voltammetric responses of both single molecule (1,2-diferrocenylethylene in 1-propyl-3-methylimidazolium bistrifluoromethylsulfonylimide) and two independent molecules (decamethylferrocene and N,N,N',N'-tetramethyl-p-phenylenediamine in 1-ethyl-3-methylimidazolium tetracyanoborate) respectively. In both systems, the difference in the formal potentials of two redox centres was measured as a function of temperature. The former was recorded as the peak difference in square wave voltammetry with the peak potential difference increases linearly with the increasing temperature. In order to show proof-of-concept in relation to a gas sensor, the latter system was investigated in the presence of oxygen, where the concentration and diffusion coefficient of oxygen varied with temperature, as well as the peak difference discussed previously, were studied in the presence of pure oxygen and dried air using chronoamperometry. A negligible variation of concentration of oxygen from both sources with temperature over the range 298 K to 318 K is demonstrated. These results obtained from pure oxygen and dried air were compared and a ca. 79% drop of cathodic signal from pure oxygen to dried air was found which is consistent with the percentage of oxygen in air. The diffusion coefficient of oxygen was related to temperature using an Arrhenius plot (natural log of diffusion coefficient as a function of reciprocal temperature), yielding a linear graph with high correlation. All experiments gave a high reproducibility.     

Novel surface acoustic wave-interdigitated array electrode gas sensor for dissolved ammonia

A novel surface acoustic wave-interdigitated array electrode (SAW-IDA) ammonia gas sensor is proposed. A gas-permeable membrane is employed to separate the buffer solution in the inner cell of the gas-sensing probe from the sample solution in the detection cell. The response of the IDA conductive electrodes is based on the impedance change of the buffer solution during ammonia adsorption. Therefore, this gas sensor overcomes the influence of water vapour in the conventional film-coated SAW gas sensor and can be used for the detection of gases in aqueous solutions. The ammonia sensor exhibits a favourable frequency response to 5 × 10⁻⁷−1 × 10⁻³ mol/1 ammonia. The optimal buffer composition and probe parameters have been determined. Dynamic range, response time, selectivity, and temperature drift are discussed. The ammonia sensor was also applied to the determination of serum ammonia. Results were in good agreement with those from the conventional enzymatic-spectro-photometric method.     

Novel surface acoustic wave-interdigitated array electrode gas sensor for dissolved ammonia

 A novel surface acoustic wave-interdigitated array electrode (SAW-IDA) ammonia gas sensor is proposed. A gas-permeable membrane is employed to separate the buffer solution in the inner cell of the gas-sensing probe from the sample solution in the detection cell. The response of the IDA conductive electrodes is based on the impedance change of the buffer solution during ammonia adsorption. Therefore, this gas sensor overcomes the influence of water vapour in the conventional film-coated SAW gas sensor and can be used for the detection of gases in aqueous solutions. The ammonia sensor exhibits a favourable frequency response to 5×10^-7–1×10^-3 mol/l ammonia. The optimal buffer composition and probe parameters have been determined. Dynamic range, response time, selectivity, and temperature drift are discussed. The ammonia sensor was also applied to the determination of serum ammonia. Results were in good agreement with those from the conventional enzymatic-spectrophotometric method. Received: 1 December 1995/Revised: 9 April 1996/Accepted: 14 April 1996     

Interpretation of static and dynamic responses of a dissolved oxygen electrode in viscous broths

The response of an amperometric oxygen electrode is studied theoretically and experimentally for the case of significant liquid film resistance at the outer side of the membrane. The behaviour of the probe in a gas stream is predicted by using a transfer function which involves an electrode model including oxygen diffusion within the electrode. The effects of the liquid film which exists at the membrane surface when dissolved oxygen concentrations are measured, are taken into account by modifying the transfer function. The new expression obtained is used to model the step response of the probe in a 2-1 stirred tank fermentor filled with water or xanthane solutions at different concentrations. First, the results are used to correct automatically the steady-state voltage readings of the probe. Secondly, the probe transfer function is used to evaluate k₁a by dynamic measurements: the response to a step change in the gas concentration is transformed via the fast Fourier transform algorithm and k₁a is identified in the Fourier domain by a Gauss-Newton algorithm. Data acquisition, Fourier transform and k₁a identification are implemented on-line on a HP-87 computer. This method of obtaining k₁a values appears to be a generalized moment method. It is shown that it is necessary to consider the liquid film dynamics around the probe in the actual fermenting conditions to evaluate k₁a successfully.     

Estimation of uncertainty in electrochemical amperometric measurement of dissolved oxygen concentration

A procedure for the estimation of measurement uncertainty of dissolved oxygen (DO) concentration measurement based on the ISO approach is presented. It is based on a mathematical model that involves 14 input parameters. The uncertainty of DO concentration strongly depends on changes in experimental details (temperature difference between calibration and measurement, the time interval between calibration and measurement, etc.). The relative measurement uncertainty is, however, practically independent of the DO concentration itself. The uncertainty is the lowest if the calibration and the measurement are done at the same temperature and on the same day. A calculation tool is provided (in the form of a GUM Workbench file) for practitioners that can be used for uncertainty calculation of DO concentrations at very different experimental conditions.Electronic Supplementary Material The uncertainty calculation example is available as a GUM Workbench calculation file C_O2_meas.smu (GUM Workbench ver. 1.3.3, Metrodata GmbH) together with its data file Input_values.xls (MS Excel 97). For those users who do not have GUM Workbench, the full report of the GUM Workbench calculation is available as a PDF file C_O2_meas.pdf. This material is available via the Internet at .     

双层纳米金修饰电极对多巴胺的测定及应用研究

利用含有连续腺嘌呤碱基模块的DNA(CA DNA)构建了双层纳米金,在此基础上制备了由聚番红花红和双层三维分布的纳米金修饰的玻碳电极,并研究了多巴胺(DA)在此修饰电极上的电化学行为,发现对于DA的氧化,CA DNA构建的电极比巯基DNA构建的电极能够起到更明显的电催化作用。利用差分脉冲法(DPV)考察了DA测定的优化条件,并发现其浓度在8.0×10-9~1.2×10-6mol·L-1范围内与氧化峰电流呈良好的线性关系。该电极用于实际样品的测定,结果满意。     

Determination of dissolved oxygen by catalytic reduction on Nafion-methyl viologen chemically modified electrode

A small size Nafion-methyl viologen chemically modified electrode (Nafion-MV CME) together with a small size electrolytic cell were constructed for the purpose of dissolved oxygen (DO) determination. The catalytic reduction of DO on Nafion-MV CME results in fast and sensitive DO determination. The mechanism of such detection is also considered.     

Oxygen measurement via phosphorescence: reaction of sodium dithionite with dissolved oxygen

A homemade instrument for the measurement of oxygen concentration in aqueous solutions measures the decay rate of the phosphorescence of a Pd-porphyrin complex (phosphor) dissolved in the solution, which is flashed every 0.1 s with 630 nm light. The concentration of O2 is a linear function of the decay rate. The instrument is used to study the reaction of dithionite (S2O42-) with O2 at 25 degrees C and 37 degrees C. It is found that the ratio of dithionite to oxygen consumed in the reaction is 1.2 +/- 0.2 at 25 degrees C and 1.7 +/- 0.1 at 37 degrees C, suggesting a temperature-dependent stoichiometry. At both temperatures, the initial rate of O2 consumption, -d[O2]/dt, is found to be 1/2 order in S2O42- and first order in O2. This finding is consistent with a previously proposed mechanism: S2O42- <--> 2SO2- comes to a rapid equilibrium, and SO2- reacts with O2 in the rate-determining step.     

The oxidase-like activity of iridium nanoparticles,and their application to colorimetric determination of dissolved oxygen

Iridium nanoparticles (IrNPs) with intrinsic oxidase-like activity were synthesized by using sodium citrate as the stabilizer and NaBH₄ as the reducing agent. The IrNPs have an average diameter of 2.5 ± 0.5 nm and exhibit excellent oxidase-like property. Under the catalytic action of the IrNPs, 3,3′,5,5′-tetramethylbenzidine (TMB) is oxidized by dissolved oxygen (DO) to form a blue product with an absorption maximum at 652 nm. The catalytic activity is ascribed to the production of superoxide anion radical (O₂ˉ?). The chromogenic reaction is exploited for the determination of DO. The method exhibits a wide calibration range from 12.5 to 257.5 μM of DO and a limit of detection as low as 4.7 μM. Compared to other methods, this method presented here shows improved precision and faster response time.

Open image in new window

Graphic abstract Iridium nanoparticles (IrNPs) stabilized by sodium citrate exhibit oxidase-like activity and can effectively catalyze dissolved oxygen (DO) by oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) to form a blue product.

     

Structurally integrated organic light emitting device-based sensors for gas phase and dissolved oxygen

A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol-gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4'-bis(2,2'-diphenylviny1)-1,1'-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime tau of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of tau in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, S(g) identical with tau(0% O2)/tau(100% O2), at 23 degrees C, were approximately 35 to approximately 50 for the [Alq3 OLED[/[PtOEP dye] pair; S(g) exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, S(DO) (defined as the ratio of tau in de-oxygenated and oxygen-saturated solutions) was approximately 9.5 and approximately 11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.     

Theory and application of cyclic voltammetry for measurement of fast electrode kinetics at microdisk electrode

An analytical expression describing voltammetric behaviors responses at microdisk electrode for various diffusion conditions and degrees of reversibility is reported in this paper. Results of theoretical calculation made it possible to use cyclic voltammetry to evaluate heterogeneous rate constants under intermediate diffusion conditions. At relatively low scan rate, the distortion of current-voltage can be reduced due to small iR drops and charging current. The effects of transfer coefficient, a, kinetic parameter, (=k0r/4D), and switching potential, s, on potential peak separation are discussed in detail. The relationship obtained in this paper between potential peak separation and \ is in good agreement with that in Ref. 14, whose authors have got their results by using digital simulation technique. After the experiment of Fe(CN)64- oxidation, k0 and a were obtained by the theory of this paper. The result agrees with that in Ref. 19.     

CODCr测量方法优化及其受营养盐胁迫研究

基于CODCr的K2 Cr2O7滴定法和HACH(哈希公司)DR6000,结合design-expert拟合分析,得到CODCr精确测量的最佳方案:消解液加入量为3 mL,K2 Cr2O7与H2 SO4-Ag2 SO4的加入比为1:5(V/V),K2Cr2O7溶液0.046 g/mL、H2SO4-Ag2SO4溶液3 g/L、HgSO40.038 g/支,恒温120℃消解2 h。同时,基于拟定的最佳方案分析了营养盐类对CODCr测定结果的影响,发现氨氮和亚硝态氮对测定结果有明显影响,而磷酸盐和偏磷酸盐对测定结果的影响较小。     

The mineral-graphite electrode and its application to the analysis of vanadium oxides

Vanadium in different oxidation states in a sample of mixed oxides can be determined by a voltammetric method without the need for decomposition of the sample. The oxide is mixed into a paste with graphite and 1-bromonaphthalene, and packed into the electrode holder. Current maxima on the polarization curves give a measure of the amount of vanadium present in each oxidation state.