Nanostructured materials in potentiometry

Potentiometry is a very simple electrochemical technique with extraordinary analytical capabilities. It is also well known that nanostructured materials display properties which they do not show in the bulk phase. The combination of the two fields of potentiometry and nanomaterials is therefore a promising area of research and development. In this report, we explain the fundamentals of potentiometric devices that incorporate nanostructured materials and we highlight the advantages and drawbacks of combining nanomaterials and potentiometry. The paper provides an overview of the role of nanostructured materials in the two commonest potentiometric sensors: field-effect transistors and ion-selective electrodes. Additionally, we provide a few recent examples of new potentiometric sensors that are based on receptors immobilized directly onto the nanostructured material surface. Moreover, we summarize the use of potentiometry to analyze processes involving nanostructured materials and the prospects that the use of nanopores offer to potentiometry. Finally, we discuss several difficulties that currently hinder developments in the field and some future trends that will extend potentiometry into new analytical areas such as biology and medicine.     

Beyond potentiometry: robust electrochemical ion sensor concepts in view of remote chemical sensing

For about 100 years, potentiometry with ion-selective electrodes has been one of the dominating electroanalytical techniques. While great advances in terms of selective chemistries and materials have been achieved in recent years, the basic manner in which ion-selective membranes are used has not fundamentally changed. The potential readings are directly co-dependent on the potential at the reference electrode, which requires maintenance and for which very few accepted alternatives have been proposed. Fouling or clogging of the exposed electrode surfaces will lead to changes in the observed potential. At the same time, the Nernst equation predicts quite small potential changes, on the order of millivolts for concentration changes on the order of a factor two, making frequent recalibration, accurate temperature control and electrode maintenance key requirements of routine analytical measurements. While the relatively advanced selective materials developed for ion-selective sensors would be highly attractive for low power remote sensing application, one should consider solutions beyond classical potentiometry to make this technology practically feasible. This paper evaluates some recent examples that may be attractive solutions to the stated problems that face potentiometric measurements. These include high-amplitude sensing approaches, with sensitivities that are an order of magnitude larger than predicted by the Nernst equation; backside calibration potentiometry, where knowledge of the magnitude of the potential is irrelevant and the system is evaluated from the backside of the membrane; controlled current coulometry with ion-selective membranes, an attractive technique for calibration-free reagent delivery without the need for standards or volumetry; localized electrochemical titrations at ion-selective membranes, making it possible to design sensors that directly monitor parameters such as total acidity for which volumetric techniques were traditionally used; and controlled potential coulometry, where all ions of interest are selectively transferred into the ion-selective organic phase, forming a calibration-free technique that would be exquisitely suitable for remote sensing applications.     

Potentiometric biosensing of proteins with ultrasensitive ion-selective microelectrodes and nanoparticle labels

We report here for the first time on the use of potentiometry for ultrasensitive nanoparticle-based detection of protein interactions. A silver ion-selective microelectrode is used to detect silver ions oxidatively released from silver enlarged gold nanoparticle labels in a sandwich immunoassay. Since potentiometry is expected to largely maintain its analytical characteristics upon reducing the sample volume, it is anticipated that this approach may form the basis for bioassays with attractive detection limits.     

Electroanalytical methods. Publications in 1999–2004

The scientometric study of publications on electrochemical methods of analysis (EMA) in a number of journals and proceedings of some conferences for 1999–2004 has been carried out. The contribution of papers on EMA to the total number of publications on analytical chemistry and the contribution of papers on individual methods (amperometry, voltammetry, including stripping and cyclic voltammetry, polarography, etc., potentiometry, including potentiometry with ion-selective electrodes, conductometry, coulometry, and other methods) to the total number of publications on EMA are estimated. Significant changes in the subject of publications, as well as in methodology and terminology, are noted over the period under review and compared to those over the earlier period. This is due to going from traditional studies to studies in the field of micro-and nanosized samples. The contributions of amperometry, electrochemiluminescence, chronoamperometry, chronopotentiometry, impedance measurements, spectroelectrochemical methods, and electrochemical microscopy have increased. It is noted that voltammetry and potentiometry are less used, but they are applied to the study of micro-and nanosized samples. In Russian publications, traditional trends of studies are retained. The contribution of publications on EMA to the total number of publications in analytical chemistry for 1946–2004 is estimated. It is ～20% on the average in the last 25 years.     

Battery-operated microcomputer-based electrochemical instrumentation

There is a need for microprocessor-controlled, battery-operated, analytical instrumentation in environmental and industrial monitoring programmes. The electrochemical techniques of ion-selective electrode potentiometry and voltammetry are ideally suited for this task because of their inherent simplicity and compatability with digital computer-based instrumentation. The task for the future is to build computerized intelligent stand-alone battery-operated devices with comparable performance to their mains-powered laboratory-based cousins.     

Analytical techniques for corrosion studies on noble metals

The suitability of various analytical methods for studying the corrosion of gold, silver and palladium in various electrolytes has been investigated. The methods included potentiometry with ion-selective electrodes, polarography and atomic-absorption spectrophotometry. All three methods are useful for monitoring low corrosion rates by solution analysis but each has its limitations. Concentrations in the ng/ml range can be measured routinely with errors of 10% or less.     

Automation of Direct Potentiometry

Abstract

A simple, versatile, automated direct potentiometry is described. It offers a wide range of possible applications for all types of ion-selective electrodes, including the glass electrode. The apparatus consists of two Fisher turntable sample changers connected to an Orion automatic switch, Orion pH/mV meter, and Orion printer system via a control module. The optimum sampling rate is 20 samples per hour F^? and NH⁺ in water samples were determined by using commercially available ion-selective electrodes.     

电分析方法测定环境和生物样品中铝含量及其形态分布研究进展

综述了用极普法、吸附伏安法、计时电位法、离子选择性电极法及流动注射分析法测定环境和生物样品中铝含量及其形态分布研究的进展和现状,比较了各种电分析方法的特点及优缺点。引用文献９７篇。     

Selectivity enhancement of anion-responsive electrodes by pulsed chronopotentiometry

A large and robust selectivity improvement of ion-selective electrodes is presented for the measurement of abundant ions. An improvement in selectivity by more than two orders of magnitude has been attained for the hydrophilic chloride ions measured in a dilute background of the lipophilic ions perchlorate and salicylate in a pulsed chronopotentiometric measurement mode. This is attributed to a robust kinetic discrimination of the dilute lipophilic ions in this measuring mode, which is not possible to achieve in classical potentiometry. Maximum tolerable concentrations of the interfering ions are found to be on the order of 30 μM before causing substantial changes in potential. As an example of practical relevance, the robust detection of chloride in 72 μM salicylate (reflecting 1:10 diluted blood) with a detection limit of 0.5 mM chloride is demonstrated. Corresponding potentiometric sensors did not give a useful chloride response under these conditions.     

Automated determination of fluoride ion in the parts per milliard range

Fluoride, down to 2 ppM, has been determined by automated direct potentiometry using a fluoride ion-selective electrode. The method reduces the dilution and contamination effects of TISAB and takes the electrode response-time into consideration. The relative standard deviation for water samples is 1.5-1.8% and the recovery varies from 96 to 107%.     

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 (I) 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. Received: 12 January 2000 / Revised: 13 March 2000 / Accepted: 16 March 2000     

Studies on the Preparation and Analytical Applications of Various Metal Ion-Selective Membrane Electrodes Based on Polymeric,Inorganic and Composite Materials—A Review

Ion-selective membrane electrodes commonly known as electrochemical sensors are important in view of the ability to make direct or indirect measurement of various metal ions. The fact is that the use of ion-selective electrodes for such type of measurements requires relatively inexpensive equipment, which makes ion-selective electrodes attractive to scientists in many disciplines. Thus, potentometric sensors can offer an inexpensive and convenient method for the analysis of heavy metal ions in solutions providing acceptable sensitivity and selectivity. For this purpose, many organic, inorganic, chelating, intercalating and composite materials were studied as electroactive materials for the preparation of ion-selective membrane electrodes. The present study provides a detailed review of literature for the fabrication, characterization and analytical applications of ion-selective membrane electrode based on different electro active components.     

Electrochemical heparin sensing at liquid/liquid interfaces and polymeric membranes

The monitoring of heparin and its derivatives in blood samples is important for the safe usage of these anticoagulants and antithrombotics in many medical procedures. Such an analytical task is, however, highly challenging due to their low therapeutic levels in the complex blood matrix, and it still relies on classical, indirect, clot-based assays. Here we review recent progress in the direct electrochemical sensing of heparin and its analogs at liquid/liquid interfaces and polymeric membranes. This progress has been made by utilizing the principle of electrochemical ion transfer at the interface between two immiscible electrolyte solutions (ITIES) to voltammetrically drive the interfacial transfer of polyanionic heparin and monitoring the resulting ionic current as a direct measure of heparin concentration. The sensitivity, selectivity, and reproducibility of the ion-transfer voltammetry of heparin are dramatically enhanced compared to those of traditional potentiometry. This voltammetric principle was successfully applied for the detection of heparin in undiluted blood samples, and was used to develop highly sensitive ion-selective electrodes based on thin polymeric membranes that are intended for analytical applications beyond heparin detection. The mechanism of heparin recognition and transfer at liquid/liquid interfaces was assessed quantitatively via sophisticated micropipet techniques, which aided the development of a powerful ionophore that can extract large heparin molecules into nonpolar organic media. Moreover, the reversible potentiometric detection of a lethal heparin-like contaminant in commercial heparin preparations was achieved through the use of a PVC membrane doped with methyltridodecylammonium chloride, which enables charge density dependent polyanion selectivity.     

Simultaneous determination of total, non-carbonate and carbonate water hardnesses by direct potentiometry

Total, non-carbonate and carbonate water hardness have been determined simultaneously by manual and automated direct potentiometry, using the bivalent ion-selective electrode, and known addition-known dilution technique. The automated and programmable system produces direct print-out of total, non-carbonate and carbonate water hardnesses. The optimum sampling rate is 20 samples per hour. This time-saving method compares well with the standard method.     

Array of potentiometric sensors for simultaneous analysis of urea and potassium

Urea biosensors based on urease immobilized by crosslinking with BSA and glutharaldehyde coupled to ammonium ion-selective electrodes were included in arrays together with potassium, sodium and ammonium PVC membrane ion-selective electrodes. Multivariate calibration models based on PCR and PLS2 were built and tested for the simultaneous determination of urea and potassium. The results show that it is possible to obtain PCR and PLS2 calibration models for simultaneous determination of these two species, based on a very small set of calibration samples (nine samples). Coupling of biosensors with ion-selective electrodes in arrays of sensors raises a few problems related to the limited stability of response and unidirectional cross-talk of the biosensors, and this matter was also subjected to investigation in this work. Up to three identical urea biosensors were included in the arrays, and the data analysis procedure allowed the assessment of the relative performance of the sensors. The results show that at least two urea biosensors should be included in the array to improve urea determination. The prediction errors of the concentration of urea and potassium in the blood serum samples analyzed with this array and a PLS2 calibration model, based on nine calibration samples, were lower than 10 and 5%, respectively.     

Separate Determination of Homologous Sodium Alkyl Sulfates with Ion-Selective Electrodes

The possibility of the separate determination of homologous sodium alkyl sulfates with ion-selective electrodes and using multisensor analysis was studied. The optimum component ratios were found for the analysis of model mixtures with ion-selective electrodes. It was shown that nonlinear regression analysis and artificial neural networks can be used for processing analytical signals from a set of weakly selective sensors for anionic surfactants.     

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.     

The computational methods in the development of a novel multianalyte calibration technique for potentiometric integrated sensors systems

In recent years, integration and miniaturization of ion-selective electrodes (ISEs) have brought many benefits resulting in the possibility of simultaneous determination of the ions concentration in small volume samples. One of the key problems related to the preparation of potentiometric integrated sensors systems (PISSs) is a calibration procedure due to the necessity to calibrate each particular sensor separately. The main aim of the research was to develop a novel calibration method for PISSs fabricated with the use of an all-solid-state technology, which has been compared with other types of sensor calibration technique. The proposed algorithm concerns the method of calibration solutions composition determination for miniature ion-selective sensors before measuring in biological samples especially human saliva samples. This article also compares the parameters of ion-selective sensors for two types of PISSs, including ISEs based on gold (Au) and glassy carbon (GC) electrodes. In addition, a series of measurements was performed using PISS with Au-ISEs in samples of human saliva, which were preceded by different types of sensor calibration and compared with the results obtained with the clinical analyzer. Moreover, the effect of the viscosity of calibration solutions on the ISE parameters and the lifetime of the sensors were investigated.

     

Polypyrrole microcapsules as a transducer for ion-selective electrodes

Polypyrrole microcapsules filled with different electrolytes were prepared using novel photopolymerization method. The obtained microstructurized material was applied as a transducer for ion-selective potentiometric sensors. In contrary to typical conducting polymer transducer, microcapsules result in introduction of significantly higher amount of exchangeable ions. Depending on the choice of electrolyte encapsulated, the resulting sensors were characterized with different analytical and electrical parameters.