Potentiometric determination of coextraction constants of potassium salts in ion-selective electrodes utilizing a nitrobenzene liquid membrane phase

A theoretical treatment of potentiometric data is applied to calculate coextraction constants (K_IA) for three potassium salts from water into a liquid nitrobenzene phase. The experiment involves treating nitrobenzene as a membrane and contacting it with two aqueous solutions of different ion activities. In the presence of either a cation or anion exchanger, the ratio of activities of ions in the two aqueous phases gives rise to a potential difference across the membrane that depends upon the nature and charge of the counter ion of the ion-exchanger in excess. Here, the cation exchanger was chosen to be potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and the anion exchanger was tetradodecylammonium chloride (TDDACl). TDDACl was incrementally added to the nitrobenzene phase containing a fixed concentration of KTpClPB, and the corresponding emf was recorded as a function of concentration of TDDACl. The membrane changes from one with cation exchanger properties (excess KTpClPB) to one with anion exchanger properties (excess TDDACl). The potential difference and shape of the titration curve can be predicted by theory based on the phase boundary potential model. Log(K_IA) values calculated for KCl, KNO₃ and KClO₄ in nitrobenzene were found as: −10.53 (± 0.09), −8.16 (± 0.05) and −5.63 (± 0.03) respectively, in accordance with the Hofmeister series of lipophilicity, and similar to those observed in PVC membranes containing other plasticizers. The method presented here offers the advantage over other methods to calculate K_IA, in that it is relatively experimentally simple without compromising the accuracy of the calculated coextraction constants. The ability to titrate directly into the liquid membrane phase affords a higher precision compared to the preparation of a series of PVC/plasticizer membranes with different compositions.     

Fabrication of a freestanding GaN layer by direct growth on a ZnO template using hydride vapor phase epitaxy

A new hydride vapor phase epitaxy (HVPE)-based approach for the fabrication of freestanding GaN (FS-GaN) substrates was investigated. For the direct formation of low-temperature GaN (LT-GaN) layers, the growth parameters were optimized: the polarity of ZnO, the growth temperature, and the V/III ratio. The FS-GaN layer was achieved by gas etching in an HVPE reactor. A fingerprint of Zn out-diffusion was detected in the photoluminescence measurements, especially for the thin (80 μm) FS-GaN film; however, a thicker film (400 μm) was effectively reduced by optimization of GaN growth.     

Sensor–actuator system for dynamic chloride ion determination

Chloride is a crucial anion for various analytical applications from biological to environmental applications. In order to measure the chloride ion concentration, a measurement system is needed which can detect this concentration for prolonged times reliably. Chronopotentiometry is a technique which does not need a long term stable reference electrode and is therefore very suitable for prolonged ion concentration measurements. As the used electrode might be fouled by reaction products, this work focuses on a chronopotentiometric approach with a separated sensing electrode (sensor) and actuating electrode (actuator). Both actuation and sensor electrode are made of Ag/AgCl. A constant current is applied to the actuator and will start the reaction between Ag and Clˉ, while the resulting Clˉ ion concentration change is observed through the sensor, which is placed close to the actuator. The time it takes to locally deplete the Clˉ ions is called transition time. Experiments were performed to verify the feasibility of this approach. The performed experiments show that the sensor detects the local concentration changes resulting from the current applied to the actuator. A linear relation between the Clˉ ion concentration and the square root of the transition time was observed, just as was predicted by theory. The calibration curves for different chips showed that both a larger sensor and a larger distance between sensor and actuator resulted in a larger time delay between the transition time detected at the actuator and the sensor.     

同时测定血清中4种电解质的流动注射微电极串联电化学自动分析系统

基于流动注射-微电极串联的动态电化学技术,建立了能快速、自动、同时测定血清中K(+),Na(+),Cl(-)和Ca(2+)的分析方法和系统,并成功用于血清样品的测定.为稳定4种电极的基线电位、加快电极响应速度,优化了载流的组分:23mmol/L Na2B4O7-H3BO3(pH 7.40),0.25mmol/L K(+...     

自动电位滴定法测定脱硫系统中氯化物

应用自动电位滴定法,在总离子强度缓冲溶液存在的情况下,在pH 5的微酸性水溶液中,用0.05mol·L~(-1)硝酸银标准溶液作为滴定剂,测定了脱硫系统样品中氯化物含量。试样用水浸取溶出氯化物,共存亚硫酸盐的干扰采用在近中性条件下加入过氧化氢煮沸至无小气泡产生予以消除,对试样的预处理方法以及各项影响测定的参数等做了试验并予以优化。方法用于测定脱硫废水、脱硫浆液和脱硫石膏样品中氯化物,加标回收率在95.7%～102.0%之间,相对标准偏差(n=5)在1.2%～5.9%之间。     

四磺酸基酞菁氯化铝复合二氧化硅干凝胶的制备及光学性能研究

采用溶胶凝胶法将不同掺杂浓度的四磺酸基酞菁氯化铝(AlClPcTS)植入二氧化硅凝胶基质,制备了均匀掺杂的复合干凝胶通过对二氧化硅凝胶基质和掺杂AlClPcTS后复合干凝胶孔结构的测定和对复合体系紫外可见吸收光谱的表征,证实了AlClPcTS在基质中的成功掺杂,并发现AlClPcTS同时以单体和二聚体的形式存在于复合体系中,且AlClPcTS二聚体所占比例随着凝胶化过程的进行而增大对不同AlClPcTS掺杂浓度复合干凝胶的光限幅性能进行了测试,并讨论了掺杂浓度对复合体系光限幅性能的影响,证明复合体系的光限幅性能随掺杂浓度的提高而增强.     

原子吸收光谱法测定粉煤灰中氧化镁

采用火焰原子吸收光谱法测定粉煤灰中氧化镁的含量。用氢氟酸-高氯酸混合酸分解样品,以氯化锶消除其他元素的干扰。本方法操作简便、再现性好、灵敏度高,氧化镁浓度在0.10—2.00μg/mL之间线性关系良好,检出限可达0.02%,适用于粉煤灰中氧化镁的测定。     

The Suitability and Usage of 18O and Chloride as Natural Tracers for Bank Filtrate at the Middle River Elbe

Abstract

Flow times and infiltration behaviour are very important for water extraction from riverbank filtration. Both the chloride content and the isotopic composition of oxygen (δ¹⁸O) were found to be suitable indicators for the conditions encountered in the middle course of the River Elbe near Torgau. The ranges for Elbe water were measured to be 20–43 mg Cl/l (1995-97) and -11 to -8.5‰ δ¹⁸O (1993-97). Both methods permitted flow-time spectra at two adjacent sampling profiles incorporating river and production wells to be obtained, indicating the preferred flow paths and the vertical extension of the riverbank filtrate plume in the aquifer. However, since the differences between the mean values for river water and regional groundwater were too small the percentage of river water abstracted from production wells could not be calculated.     

Surface chemistry and transport effects in GaN hydride vapor phase epitaxy

A simple quasi-thermodynamic model of surface chemistry in GaN hydride vapor phase epitaxy (HVPE) is presented. The model is coupled with the detailed 3D simulations of species transport in a horizontal-tube reactor and validated by the comparison with the data on the GaN growth rate obtained by laser reflectometry. Parametric study of the growth rate as a function of temperature and species flow rates has been performed over a wide range of growth conditions. The important role of species transport in an HVPE reactor is demonstrated. In particular, a strong effect of the natural concentration convection resulting in the formation of recirculation zones and in a non-uniform vapor composition is revealed by modeling. The impact of these effects on the GaN growth rate and V/III ratio on the growth surface is discussed in detail.     

Development of an anodic stripping voltammetric assay, using a disposable mercury-free screen-printed carbon electrode, for the determination of zinc in human sweat

This paper reports on the development of a novel electrochemical assay for Zn²⁺ in human sweat, which involves the use of disposable screen-printed carbon electrodes (SPCEs). Initially, SPCEs were used in conjunction with cyclic voltammetry to study the redox characteristics of Zn²⁺ in a selection of supporting electrolytes. The best defined cathodic and anodic peaks were obtained with 0.1 M NaCl/0.1 M acetate buffer pH 6.0. The anodic peak was sharp and symmetrical which is typical for the oxidation of a thin metal film on the electrode surface. This behaviour was exploited in the development of a differential pulse anodic stripping voltammetric (DPASV) assay for zinc. It was shown that a deposition potential of −1.6 V versus Ag/AgCl and deposition time of 60 s with stirring (10 s equilibration) produced a well-defined stripping peak with E_pa = −1.2 V versus Ag/AgCl. Using these conditions, the calibration plot was linear over the range 1 × 10⁻⁸ to 5 × 10⁻⁶ M Zn²⁺. The precision was examined by carrying out six replicate measurements at a concentration of 2 × 10⁻⁶ M; the coefficient of variation was calculated to be 5.6%. The method was applied to the determination of the analyte in sweat from 10 human volunteers. The concentrations were between 0.39 and 1.56 μg/mL, which agrees well with previously reported values. This simple, low-cost sensitive assay should have application in biomedical studies and for stress and fatigue in sports studies.