Multisensor system on the basis of an array of non-specific chemical sensors and artificial neural networks for determination of inorganic pollutants in a model groundwater

The application of a multisensor system to groundwater monitoring is investigated. The sensor system is based on an array of non-specific potentiometric chemical sensors with data processing by artificial neural networks and includes 13 sensors with PVC membranes and 12 solid-state ones. Results of measurements in model solutions containing heavy metals, alkali- and alkali-earth cations and inorganic anions at concentrations typical for groundwater near the city of Braunschweig, Germany, are presented. Both the response of the whole sensor array and the responses of subsystems consisting only of PVC and only of solid-state sensors, respectively, are investigated. It is shown that both subsystems can be used for determination of described ions and that the best results are obtained if the whole array of sensors is used.     

Polypyrrole-calcion film as a membrane and solid-contact in an indicator electrode for potentiometric titrations

This paper shows the application of conducting polymers (CPs) for constructing potentiometric indicator electrodes. Two types of polypyrrole (PPy)-based calcium sensors are presented, one sensor with PPy-calcion film as the active part and the other sensor with PPy-calcion as a solid-state contact coated with a conventional membrane selective towards calcium ions. It is shown that the PPy-calcion film, due to the complexing properties of calcion ensuring high loading of the film with calcium, is sufficiently selective to be used as the active part or as a mediating layer of the indicator electrode. The electrode, with PPy-calcion film as the active part, was used as the indicator electrode in potentiometric titrations of calcium in mixed solvents, where conventional PVC-based electrode can not be used. For the first time, the practical applicability of PPy-based electrodes in titrations is demonstrated.     

Non-selective chemical sensors in analytical chemistry: from “electronic nose” to “electronic tongue”

Development, recent historical background and analytical applications of promising sensor instruments based on sensor arrays with data processing by pattern recognition methods have been described. Attention is paid to the “electronic tongue” based on an array of original non-specific (non-selective) potentiometric chemical sensors. Application results for integral qualitative analysis of beverages and for quantitative analysis of biological liquids and solutions, containing heavy metals are reported. Discriminating abilities and precision obtained allow to consider “electronic tongue” as a perspective analytical tool.     

Functional layers for chemical sensors based on conducting polypyrrole

Functional thin layers based on polypyrrole were used in electrochemical sensors as mixed conducting interfaces between ion‐selective membranes and the wiring. In particular, new types of ion‐selective electrodes for potentiometric measurement of pH value and concentration of sulfate ions in solutions were developed. The resulting electrodes do not need any inner liquid junction. First determinations of the sensor parameters sensitivity, selectivity and long term stability indicate a good performance of the prepared sensors. The results imply that interfaces, containing polypyrrole, could be an interesting basis for the construction of a new type of all‐solid‐state ion‐selective electrodes.     

Simultaneous Quantification of Heavy Metals Using a Solid State Potentiometric Sensor Array

A potentiometric sensor array of four nonspecific electrodes with solid‐state membranes is developed and tested for simultaneous analysis of copper(II), mercury(II), and silver(I) ions. The cross‐sensitivity responses of the sensors for these ions are evaluated. The array potentiometric signals are processed by partial least‐squares regression (PLS) and back propagation artificial neural networks (ANN) to determinate analyte concentrations. The ANN configuration is optimized and two different training algorithms of the ANN are also evaluated. Best results are obtained when the potentiometric sensors are activated and the data are processed using ANN and the gradient descent adaptive algorithm. The system is used to quantify these heavy metals in synthetic samples and in dental amalgams with successful results.     

Non-selective chemical sensors in analytical chemistry: from “electronic nose” to “electronic tongue”

Development, recent historical background and analytical applications of promising sensor instruments based on sensor arrays with data processing by pattern recognition methods have been described. Attention is paid to the “electronic tongue” based on an array of original non-specific (non-selective) potentiometric chemical sensors. Application results for integral qualitative analysis of beverages and for quantitative analysis of biological liquids and solutions, containing heavy metals are reported. Discriminating abilities and precision obtained allow to consider “electronic tongue” as a perspective analytical tool. Received: 17 July 1997 / Revised: 19 February 1998 / Accepted: 24 February 1998     

Coated film electrodes

Summary The construction of coated-film electrodes is described. It is shown that they are miniaturizable, inexpensive, simple sensors for various cations and anions. They are similar to the coated-wire electrodes, but instead of a metal wire an extremely thin conductive metal layer manufactured in thin-film technology is used. Potassium and sodium electrodes studied so far show excellent electrode properties, i. e. near Nernst response over a wide concentration range, sometimes better than commercial ion-selective electrodes. Two film electrodes are used to develop a low cost sensor for the determination of the activity of ions in a simple way by potentiometric difference measurement; this solid-state sensor can be applied to biomedical measurements, especially for blood analysis.

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Filmelektroden

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

革除或减少增塑剂的敏感膜离子选择电极

基于国内外最新研究工作,系统总结了离子选择电极膜中革除或减少外增塑剂的新膜基体,包括丙烯酸酯类聚合物、羟基功能化的乙烯基树脂、聚氨酯、硅橡胶以及导电聚合物,对其物理化学性能以及传感器检测等进行了全面归纳与讨论.指出该类革除外增塑剂的传感膜不仅避免了增塑剂的泄漏及其对生物样品的污染,而且较传统增塑聚氯乙烯(PVC)膜扩散系数降低了约3个数量级,有利于抑制过膜离子流,使其检测下限较传统增塑PVC下降了5个数量级,且选择系数也有不同程度的改善.另外,该类传感膜材料由于与固体支撑材料间优良的粘附性保证了电极的使用寿命,特别是在微型化固态电极中.以这类传感膜构建的电位型离子传感器将以其独特的优势在环境监测、食品卫生,尤其是在医疗诊断、生物物质检测中展示出不可替代的作用.     

Potentiometric carbon paste sensors for lead(II) based on dithiodibenzoic and mercaptobenzoic acids.

Dithiodibenzoic (DTB) acid and mercaptobenzoic (MB) acid were studied to characterize their abilities as modifier agents for lead(II) sensors. For both sensors, the best results were obtained with modified carbon paste electrodes with 24.1% of ligand. The pH influence on the potentiometric response was studied. The selectivity coefficients for both modified electrodes were tabulated. A potentiometric sensor based on DTB acid exhibited a more sensitive and selective response to lead ions than an MB electrode. The limits of detection for the DTB and MB electrodes were very similar, 5.01 x 10(-8) M and 3.98 x 10(-8) M, respectively, for lead(II) activity. The DTB sensor was applied to lead(II) ion determination in real samples and as an indicator electrode in potentiometric titrations. Natural and commercial humic acids were titrated using the DTB electrode to estimate the stability constant between these organic compounds and the lead(II) ions with successful results.     

Ionic Liquids Modify the Performance of Carbon Based Potentiometric Sensors

A new type of potentiometric sensor based on a recently constructed carbon ionic liquid electrode (CILE) is described. Two kinds of ionic liquids, i.e., N‐octylpyridinium hexafluorophosphate (OPFP) and 1‐butyl‐3‐methylimidazoluim hexafluorophosphate (BMFP) were tested as binder for construction of the carbon composite electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with those of the traditional carbon paste electrode (CPE). The results indicate that potentiometric sensors constructed with ionic liquid show an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to CPE.     

Measurement of pork freshness using potentiometric sensor

This study evaluated pork freshness using potentiometric solid-state electrodes in order to detect chemical indices such as reduced compounds, organic compounds and sulfides, which are produced during the initial stage of putrefaction in meat. Pt, CuS and Ag₂S electrodes selected as solid-state electrodes have, respectively, been used to detect the organic compounds (regarded as chemical indices of deterioration in meat freshness). The outputs of these electrodes have been analyzed by principal component analysis (PCA) and multiple regression analysis (MRA) in order to find the correlation with the results of viable bacterial counts. By using the potentiometric sensor, the pork freshness was evaluated and the PCA and MRA corresponded to the degree of bacterial increases more simply and rapidly than other methods such as viable bacterial counts or a biosensor.     

Solid-state reference electrodes for potentiometric sensors

The availability and application of solid-state reference electrodes for potentiometric electrochemical sensors are briefly reviewed. For a long time, considerable efforts have been made to combine solid-state indicator electrodes with equivalent reference electrodes to take advantage of the absence of liquid system components to full capacity. In spite of various suggestions to solve the problem, no type of solid-state reference electrode is so far available with properties completely identical to conventional ones.     

New electroanalytical applications of self-assembled monolayers

New applications of self-assembled monolayers of thiol compounds on gold electrodes are reviewed. They include: (i) exploitation of electrical control of self-assembly of thiol compounds for electrically-addressable immobilization of receptor molecules onto sensor arrays; (ii) a spreader-bar technique for formation of stable nanostructures; and, (iii) use of self-assembled monolayers as selective filters for chemical sensors.     

A Solid-State Reference Electrode Based on a Self-Referencing Pulstrode

The design of solid-state reference electrodes without a liquid junction is important to allow miniature and cost-effective electrochemical sensors. To address this, a pulse control is proposed using an Ag/AgI element as reliable solid-state reference electrode. It involves the local release of iodide by a cathodic current that is immediately followed by an electromotive force (EMF) measurement that serves as the reference potential. The recapture of iodide ions is achieved by potentiostatic control. This results in intermittent potential values that are reproducible to less than one millivolt (SD=0.27 mV, n=50). The ionic strength is shown to influence the activity coefficient of released iodide in accordance with the extended Debye–Hückel equation, resulting in a predictable change of the potential reading. The principle is applied to potentiometric potassium detection with a valinomycin-based ion-selective electrode (ISE), demonstrating a completely solid-state sensor configuration.     

Solid-state potentiometric gas sensors—current status and future trends

The development of potentiometric sensors for monitoring environmental gases has become a well-established direction in sensor technology. Various types of potentiometric sensors employing solid electrolytes for in situ measurements of such gases as oxygen, hydrogen, carbon dioxide, sulfur oxides, carbon monoxide, nitrogen oxides, and hydrocarbons are reviewed. Particular concern was given to the CO₂ potentiometric sensor which is an example of successful commercial application. The construction details, working mechanism, and performance of different types of potentiometric gas sensors are given. Special emphasis is given for the mixed-potential electrodes, which seems to be the principal direction for the future research and development of the sensor science and technology. Additionally, the future use of potentiometric sensors for the detection of other environmental gases is discussed.     

Screen-printed copper ion-selective electrodes

A simple, low-cost and reproducible method for the mass production of potentiometric ion-selective electrodes for copper ions is presented. These planar, strip sensors were obtained by screen-printing. The application of pastes cured at low temperature allows printing of the sensors on low-cost, plastic substrates. The pastes for printing of ion-sensitive thick-film membranes were based on copper (1) and copper (II) sulfides. The analytical characteristics of the thick-film electrodes were compared. The analytical properties (range of determination, sensitivity, selectivity, response time) of the copper (I) sulfide-based sensors were comparable with those for conventional ion-selective electrodes.     

Silver and lead all-plastic sensors—polyaniline vs. poly(3,4-ethyledioxythiophene) solid contact

Silver and lead selective all-plastic ion-selective electrodes were obtained using poly(vinyl chloride)-based membranes and either poly(3,4-ethylenedioxythiophene) or polyaniline dispersion cast on an insulating plastic support as transducer and electrical lead. The effect of interactions of applied conducting polymer with analyte ions on potentiometric responses was evaluated and correlated with changes in elemental composition and element distribution within the ion-selective membrane and the conducting polymer transducer revealed in course of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) experiments. In the case of silver selective electrodes, potentiometric responses obtained are much dependent on the oxidation state of the polymer placed beneath the ion-selective membrane. For semi-oxidized polymer (poly(3,4-ethylenedioxythiophene)-based electrodes, linear responses with detection limit equal to 10^−5.4 M were obtained. For a more oxidized polyaniline (of higher conductivity), although the electrodes were pretreated exactly in the same way and tested in parallel, super Nernstian potential slope was recorded within the AgNO₃ activities range form 10⁻⁶ to 10⁻⁷ M. These responses were consistent with results of LA-ICP-MS, revealing profoundly higher silver signals intensities for poly(3,4-ethylenedioxythiophene) underlying silver selective membrane. It seems highly probable that silver is accumulated in this polymer layer as Ag⁰ due to spontaneous redox reaction leading to oxidation of the polymer; however, this process requires also the presence of silver ions at the interface. In fact, when reduced (deprotonated) polyaniline was used as transducer, the potentiometric responses of the sensor were, within the range of experimental error, the same as obtained for poly(3,4-ethylenedioxythiophene)-based sensor. On the other hand, for lead(II) selective sensors, the difference in responses of electrodes prepared using poly(3,4-ethylenedioxythiophene) or polyaniline was less pronounced, which is in accordance with the elemental composition of these sensors.     

氧化钯作为电位型传感器中敏感电极的工作机理

This paper describes the sensing properties of a potentiometric sensor based on a palladium oxide (PdO) electrode. Our investigation of the sensing mechanism is also discussed. We studied carbon monoxide (CO) sensing performance of a PdO electrode doped with Mg, Ni, and La, printed on zirconia. The results indicated that defects on the surface of PdO, which allow adsorption of CO, can effectively enhance the sensitivity of the sensors. To explore the source of the signal, a PdO-based electrode was printed on an alumina disc and a zeolite pellet for CO detection at 450℃. Notably the zeolite coupled with the PdO-based electrode to generate potentiometric responses to changes in CO concentration. According to the resistance and impedance measurements, the response to CO was ascribed to the changing interfacial potential between the PdO electrode and electrolyte. A model based on an electrochemical double layer between the PdO and electrolyte was determined to explain the behavior of the potentiometric sensor. It may be possible to harness these effects at PdO electrodes for the development of electrochemical sensors.     

Voltammetric Properties of All‐solid State Ion‐selective Electrodes with Multiwalled Carbon Nanotubes‐poly(3‐octylthiophene‐2,5‐diyl) Nanocomposite Transducer

Voltammetric response of an all‐solid‐state ion‐selective electrode was studied on example of potassium‐selective sensor with poly(vinyl chloride) based membrane and nanocomposite transducer containing poly(3‐octylthiophene‐2,5‐diyl) and multiwalled carbon nanotubes. Factors limiting the rate of the electrochemical process and the response were discussed. The challenge in voltammetric applications of ion‐selective electrodes is thickness of the plastic membrane. It was found that although a relatively thick ion‐selective membrane was applied, as typically used in potentiometric studies, the position of the reduction peak, corresponding to potassium ions incorporation, was dependent on ions concentration in a Nernstian manner. This opens possibility of deviation from the paradigm of ultrathin membranes in voltammetric applications, thus potentially extending the sensors lifetime. The high resistance of the membrane did not affect the voltammetric characteristics, because the resistance was independent of ions concentration in solution. On the other hand, high resistance results in charge trapping effect in the solid contact material, leading to advantageous retention of the oxidized‐conducting state of the solid contact, independently of the applied electrode potential.     

Galvanic cell without liquid junction for potentiometric determination of copper

This paper describes potentiometric measurements in an integrated galvanic cell with both indicator and reference electrodes. Both electrodes are conducting polymer-based. The copper-sensitive indicator electrode is made by using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with 2-(o-arsenophenylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic sodium salt (Arsenazo-I) as the electroactive substance in the film, while the reference electrode is based on PEDOT doped by 2-morpholineoethanesulfonic acid (MES). It is shown that the galvanic cell can be used for determination of copper both in non-aqueous media (where all PVC-based membranes failed) and in the presence of chloride ions, which disturb the signal of conventional copper ion-selective electrodes with solid-state membranes. It is further shown that the titration of copper ions can be successfully monitored using the described electrochemical cell.