控制电位滴定法的误差分析

研究了影响控制电位滴定法测定结果准确度的因素,得到的结论是:第一,电位的控制误差及滴定剂体积的测定误差是影响控制电位滴定法测定结果准确度的主要因素.计算模型中的比例系数越大,滴定曲线的变化率越大,这种影响越小.第二,多组分体系的测定误差,与组分在计算模型中比例系数的相对大小有关.比例系数越大,测定误差越小.第三,不同浓度(或不同浓度比)待测溶液滴定曲线的差异越大,对控制电位滴定法的测定越有利.     

等电位间隔-电位滴定法

对两点电位滴定法作出改进,提出了等电位间隔-电位滴定法。由数学推导证明,当P1的数值(P1为V1与Ve的比值以百分率表示;V1为在第1测量点所耗滴定剂的体积;Ve为滴定终点时所耗滴定剂的体积)达到95%,且在两点间的电位差值(ΔE)大于30mV时,滴定的相对误差(T)的计算值可达到小于0.1%。据此,在滴定过程中,记录两测量点之间的ΔE为30mV时的V及E值,当有两组数据的ΔE达到30mV并算得此时的T值≤0.1%时,即可停止滴定,并根据所给公式计算Ve及滴定结果。将此方法应用于包括中和反应、沉淀反应及氧化还原反应等多种滴定体系的电位滴定,所得结果与常规电位滴定法的测定结果一致。     

控制电位电解法测定银合金中的银

利用控制阴极电位的方法,在氨性介质中,以EDTA作掩蔽剂对银合金中的银进行电解,消除了一定量的共存离子干扰,提高了银的回收率.在电解分析中,严格控制阴极电位,提高了方法的灵敏度.将该法用于银合金中银的测定,回收率为99.6%～99.8%,测定结果的相对标准偏差RSD为0.15%～0.17%(n=4).     

示波电位滴定法测定COD的研究

本文用回流处理样品，以示波电位滴定法测定水中化学耗氧量（ＣＯＤ），方法简单，终点变化敏锐，特别适宜于有色和有悬浊物的样品分析。     

氯离子选择性电极电位法测定光气含量

光气是医药、染料、农药等有机合成的重要原料,也是剧毒的气体。因此,对光气的分析测定也是十分重要。分析光气的方法颇多,诸如气相色谱法、高压液相色谱法、吸光光度法等。但用离子电极法国内外报道者甚少,曾查阅到日本专利报道过用玻璃电极法测光气,由于文献不全未进行验证。本文根据氯离子的电化学特性采用氯离子电极探讨了光气含量的氯离子选择性电极电位测定法。对光气合成或环境保护监测具有一定的实用和参考价值。     

锂在铝合金电极上的析出电位和扩散系数

铝锂合金是一种新型的航空材料,近十年来获得了迅速的发展。1985年发展了熔盐电解法制备铝锂合金新工艺。该法与其他物理冶金法相比,具有节省能源,设备简单,合金产品纯度高等优点。本文测得的析出电位及扩散系数为熔盐电解法制备铝锂合金提供了重要的参考数据。     

零流电位法在酸碱滴定中的应用研究

探讨了零流电位法在酸碱滴定中的检测原理及应用,通过考察强碱滴定弱酸、强碱滴定强酸、强酸滴定弱碱以及强酸滴定强碱四种滴定体系,探明了零流电位法在酸碱滴定中的适用性。通过氢氧化钠滴定醋酸对本方法进行评价,实验结果表明:本法的相对误差为-0.4%,同一根电极的滴定值的相对标准偏差(RSD)为0.4%(n=5),同一根电极五天滴定值的RSD为0.6%,五根电极滴定值的RSD为0.5%。本方法具有较高的准确性、稳定性和重现性。     

自动电位滴定法测定铜精矿中高含量氯

使用无水碳酸钠-氧化锌混合熔剂焙烧半熔铜精矿样品,分离大量的基体元素,用沸水浸取半熔物,在乙醇-水溶液中用硝酸银标准溶液电位滴定测定试液中的氯量;利用氯与银发生化学反应生成氯化银沉淀的原理以及电位突跃判断滴定终点。方法操作简单快速,重现性好,适应性强,可准确测定铜精矿中高含量氯(0.10%~5.00%)。     

Evaluation of Electrochemically Reduced Gold Nanoparticle—Graphene Nanocomposites for the Determination of Dopamine

Two gold nanoparticle-graphene nanocomposites were electrochemically obtained by the one-step constant potential coreduction of graphene oxide and gold ions or the electrodeposition of gold nanoparticles on graphene oxide followed by electrochemical reduction of graphene oxide. The surface morphology, electron transfer rate, and electrocatalytic activity toward the oxidation of dopamine on these nanocomposites were systematically studied. The results showed that both preparations synthesized gold nanoparticle-graphene nanocomposites. The nanocomposite obtained by the one-step synthesis showed higher electron transfer kinetics and electrocatalytic activity toward dopamine than the material obtained by the two-step synthesis. Consequently, the one-step nanocomposite was used to modify a glassy carbon electrode to form a dopamine sensor. Differential pulse voltammetry was used to detect dopamine with a detection limit of 0.1 micromolar and a linear dynamic range from 0.2 to 20 micromolar. The sensor displayed good stability, high reproducibility, and was used for the determination of dopamine in human urine.     

Integrated electrochemical transistor as a fast recoverable gas sensor

A new design of conductometric chemical sensors based on conducting polymers as chemosensitive elements was suggested. The sensor includes six electrodes. Four inner electrodes coated by chemosensitive polymer are used for simultaneous two- and four-point resistance measurements thus providing information on the bulk polymer resistance and on the resistance of the polymer/electrode contacts. Two outer electrodes wired to inner electrodes by polymeric electrolyte are used for electrical control of redox state of the chemosensitive polymer. The outer electrodes are connected to potentiostat as reference and counter electrodes. It allows us to control redox state of the inner (working) electrodes. This new measurement configuration, resembling chemosensitive electrochemical transistors, provides an internal test of the sensor integrity and an electrically driven sensor regeneration. It was tested as a sensor for the detection of nitrogen dioxide. Polythiophene or polyaniline was used as receptors. Cyclic voltammograms of these polymers on the sensor surface measured in air atmosphere were very similar to that measured in aqueous electrolyte. A control of conductivity of these chemosensitive polymers by electrical potential applied vs. incorporated reference electrode was demonstrated. This effect was used for the regeneration of the chemosensitive material after exposure to nitrogen dioxide: in comparison to usual chemiresistors displaying an irreversible behavior in such test even in the time scale of hours, a completely reversible sensor regeneration within few minutes was observed.     

Internal solid contact sensor for the determination of doxycycline hydrochloride in pharmaceutical formulation

The internal solid contact sensor for the determination of doxycycline hydrochloride (DC) was developed based on a conducting polypyrrole (PPy) film immobilized on a glassy carbon electrode surface casted by a plasticized polyvinyl chloride (PVC) membrane containing an ion-pair compound of DC with tetraphenylborate (TPB) and dibutylphthalate (DBP) as plasticizer. Effects of various factors for the electropolymerization of pyrrole or aniline, including monomer concentration, acidity or inorganic salt and thickness of polymer film were investigated experimentally. It was found that the slope and the linear range of SCSs changed with both the different concentration of monomer and of KCl in electrolyte solution and with the different substrate material and a marked influence of the change of solution pH on the potential response of sensor occurred when sample solution pH>3.5. Under the condition of pH 2.8, the sensor showed a near-Nernstian response over the range of DC concentration of 1.0x10(-2)-1.0x10(-5) mol l(-1) with the slope (at 25 degrees C) of 54.4 mV per decade. The detection limit obtained was 4.0x10(-6) mol l(-1).The sensor was successfully applied to determination of DC in pharmaceutical formulation.     

Modeling of hydrocarbon sensors based on p-type semiconducting perovskites

In the scope of the present contribution, perovskite SrTi(1-x)Fe(x)O(3-delta) was investigated as a model material for conductometric hydrocarbon sensing at intermediate temperatures between 350 and 450 degrees C. To explain the observations made during sensor optimization in a quantitative way, a novel sensor model was proposed. At the microscopic scale, the local gas concentration affects local conductivity of the gas sensitive material. In the case of n-type tin oxide sensors, this interaction is commonly attributed to a redox reaction between the reducing analyte gas and adsorbed oxygen. In contrast, a reduction process affecting the entire bulk was assumed to govern gas sensitivity of SrTi(1-x)Fe(x)O(3-delta) films. Although very few variables needed to be assumed or fitted, the present bulk-type model was found to represent well sensor functionality of p-type conducting SrTi(0.8)Fe(0.2)O(3-delta) films. In addition to the temperature dependence of sensor response, the hydrocarbon sensitivity, m, was predicted with good accuracy. The different sensor responses towards hydrocarbons with a different chemical reactivity and other cross-interfering species, such as NO, was explained as well as the dependence on film thickness for screen printed films.     

Magnetically Assembled Multisegmented Nanowires and Their Applications

Here we report a cost effective and versatile way of synthesizing and assembling multi‐functional (e.g., gold‐polypyrrole‐nickel‐gold) nanowires. Multisegmented nanowires were synthesized using electrodeposition method for precise control over segment dimensions for proper expression of material functionality. The nanowires were integrated on microfabricated electrodes using magnetic dipole interactions between the ferromagnetic segment in the nanowire and the ferromagnetic electrodes. The electrical properties of multisegmented nanowires showed semiconducting behavior with the activation energy of ca. 0.27 eV for the conducting polymer segment of the nanowire. These nanowire devices showed response towards light and exposure to ammonia, demonstrating their potential use as photonic device and gas sensor, respectively.     

Research Progress on Nitrite Electrochemical Sensor

Nitrite has been widely used in industrial and agricultural production and is commonly found in food, drinking water, biology and environment. However, nitrite is a toxic inorganic pollutant that is very harmful to the health of human and other organisms. A variety of strategies have been proposed for nitrite detection in recent years. Among which, electrochemical approaches have gained more and more attention owing to the characteristics of simplicity, speediness, high sensitivity, and low cost, etc. The principle of nitrite electrochemical sensor is recommended in this review. The research progresses of nanocomposite material sensor for electrochemical nitrite detection based on carbon material, metal material, metal organic framework, conducting polymer and enzyme in recent years are also introduced from the perspective of composite electrode modification layer. The construction approaches and sensing performances of modified electrode are put special emphasis. At last, future trends of nitrite electrochemical sensor are discussed.     

Fabrication of an ammonia gas sensor using inkjet-printed polyaniline nanoparticles

This work details the fabrication and performance of a sensor for ammonia gas analysis which has been constructed via the inkjet-printed deposition of polyaniline nanoparticle films. The conducting films were assembled on interdigitated electrode arrays and characterised with respect to their layer thickness and thermal properties. The sensor was further combined with heater foils for operation at a range of temperatures. When operated in a conductimetric mode, the sensor was shown to exhibit temperature-dependent analytical performance to ammonia detection. At room temperature, the sensor responded rapidly to ammonia (t₅₀ = 15 s). Sensor recovery time, response linearity and sensitivity were all significantly improved by operating the sensor at temperatures up to 80 °C. The sensor was found to have a stable logarithmic response to ammonia in the range of interest (1-100 ppm). The sensor was also insensitive to moisture in the range from 35 to 98% relative humidity. The response of the sensor to a range of common potential interferents was also studied.     

Electrochemical Characterisation of Polypyrrole Doped with p‐Sulfonatocalix[4]arene

Polypyrrole (PPy) films doped with macrocyclic calixarene anions are attractive materials for the development of selective sensor materials and membrane systems as the incorporation of the macrocycles can confer specific recognition sites within the polymer matrix. However, unlike many other PPy films a calixarene‐doped system is more complicated as calixarenes are themselves electroactive. Here we present results on the electroactivity, impedance properties and morphology of polypyrrole doped with p‐sulfonatocalix[4]arene. The calixarene in the polymer was found to be irreversibly oxidised at potentials greater than 0.500 V vs. SCE and reacted to form a new redox active species that was trapped within the polymer matrix. The results from the impedance and EQCM studies indicated that the calixarene was permanently trapped within the polymer matrix and the polymer acted as a cation exchange material. In addition, the data acquired from the EQCM experiments showed that while the material displayed simple cation exchange properties at high scan rates, at lower scan rates the transport of neutral species was also observed. Overall, our findings indicate that the PPy‐C4S system is suitable for use as a stable conducting polymer doped with an immobile anion within the potential window of ?0.800 V to 0.500 V vs. SCE.     

Rapid and quantitative method for evaluating the personal therapeutic potential of cancer drugs

An in vitro, rapid, and quantitative cell-based assay is needed to predict the efficacy of cancer drugs in individual patients, because a cancer patient may have unconventional aspects of tumor development. Here we report a rapid and label-free quantitative method for verifying apoptosis in living cancer cells cultured on a sensor chip with a newly developed high-precision surface plasmon resonance (SPR) sensor. The time-course cell reaction was monitored as the SPR angle change rate for 5 min during a 35-min cell culture of pancreatic cancer lines with a drug. The time-course cell reaction was significantly related to cell viability counted after 48 h as assessed by caspase-3 activity assay of apoptosis. Furthermore, the detected SPR signal was derived from the decrease in inner mitochondrial membrane potential. The results obtained are universally valid for various cancer drugs mediating apoptosis through different cell-signaling pathways and even for combined use in various pancreatic cancer cell lines. This system can be applied in a clinical setting to evaluate the personal therapeutic potential of drugs including pharmacodynamic interactions.     

Study of polyaniline conducting/electroactive polymer as sensor for some agricultural phosphorus pesticides

Abstract  

Due to their wide applications as insecticides, pesticides, chemical warfare agents, etc., detection of organophosphorus compounds is of great importance. This paper deals with application of polyaniline conducting polymer (PANi) as a sensor material for detection of some agricultural organophosphorus compounds that are commonly used as insecticides and pesticides. The compounds employed in this investigation are dichlorvos, trichlorophon, and chlorpyrifos. The effects of some important parameters such as concentration, thickness of the polymer film, etc., on electrical conductivity and conductivity stability for these compounds have also been investigated. In situ electrical conductivity measurements were performed using a standard direct-current (DC) four-point probe technique. It was found that adsorption and desorption of these compounds on PANi film cause measurable change in the resistance of conducting polymers.