This article reviews recent advances in the field of potentiometric solvent polymeric membrane electrodes. These sensors have found widespread applications in a variety of fields, especially in the area of clinical diagnostics. Emphasis is given on the discussion of the theoretical and practical limits of ionophore-based ion-selective electrodes, with a special focus on electrode sensitivities, characterization of selectivities and dramatic improvements in detection limits. Advances in ionophore design and in the underlying model assumptions are also discussed. It is shown that a multitude of exciting new research possibilities have recently emerged in this well—established field.

Polymer Membrane Ion-Selective Electrodes–What are the Limits?

Cadmium(II)-selective sensors based on dibenzo-24-crown-8 in PVC matrix

This paper introduces electronic tongue systems for remote environmental monitoring applications. This new approach in the chemical sensor field consists of the use of an array of non-specific sensors coupled with a multivariate calibration tool which may form a node of a sensor network. In our work, the proposed arrays were made up of potentiometric sensors based on polymeric membranes, and the subsequent cross-response processing was based on a multilayer artificial neural network model. Two cases are described: the environmental monitoring of ammonium pollutant plus alkaline ions at different measuring sites in the states of Mexico and Hidalgo (Mexico), and the monitoring of heavy metals (Cu^2^+, Pb^2^+, Zn^2^+ and Cd^2^+) in open air waste streams and rivers heading down the Gulf of Mexico.

A review of the use of the potentiometric electronic tongue in the monitoring of environmental systems

The potentiometric response characteristics of electrodes based on N , N ′-bis(acetylacetone)ethylenediimine ( I ) in poly(vinyl chloride) (PVC) combined with an anion localizing agent (sodium tetraphenyl borate, NaTPB) and solvent mediators, viz. o -nitrophenyl octyl ether (NPOE), dibutyl (butyl) phosphonate (DBBP), tri- n -butyl phosphate (TBP) and chloronaphthalene (CN) were investigated. The best result for Zn 2+ -sensing was obtained for the electrode membrane of the composition of I :PVC:NaTPB:NPOE = 5:100:6:200, where the electrode had a Nernstian response (30.0 mV/decade of Zn 2+ activity) to Zn 2+ within the concentration range of 1.0 × 10 −6 to 1.0 × 10 −1  M. The operational pH range of the electrode was 3.2–7.1. Selectivity characteristic of the proposed electrode was also assessed by calculating K A , B Pot with a fixed interference method. The sensor has been successfully used in real sample analysis and also in the potentiometric titration of zinc ions with EDTA.

A zinc-selective electrode based on N,N′-bis(acetylacetone)ethylenediimine

Potentiometry with ion!selective microelectrodes measures activity of specific cations and anions at the solid/liquid interface from the solution side. Anodic and cathodic components of corrosion processes change local concentration of H + , OH ! , metal cations and ions of the supporting electrolyte. These changes can be detected and quantified by SIET, making this technique an alternative, or complement, to methods based on potential and current changes across the interface. This mini!review describes SIET basics and demonstrates several examples of SIET applications relevant to corrosion studies.

In-situ visualization of local corrosion by Scanning Ion-selective Electrode Technique (SIET)

A poly(vinyl chloride) membrane electrode that is highly sensitive and selective for zinc ions has been developed by using tetrabutyl thiuram disulfide neutral carrier. This electrode incorporated the ionophore along with o-nitrophenyloctyl ether as a plasticizing solvent mediator and potassium tetrakis(p-chlorophenyl)borate as anion excluder; it exhibited a linearity range of 10-1-10-6M with a Nernstian slope of 28.0mV per decade at 25±1°C. The membrane electrode showed a good response to zinc ions in the useful pH range of 3.5 to 6.5, where interferences arise only from a few transition metals such as CuII and PbII.

Ryuji Kojima

Papers

Zinc-selective membrane electrode using tetrabutyl thiuram disulfide neutral carrier