Conventional Ion-selective Electrodes Research Articles

Ion-selective electrode with fixed quaternary phosphonium ion-sensing species

The response properties and selectivity of polymer membrane electrodes with fixed quaternary phosphonium ion-sensing groups for nitrate are described. A poly(trioctylvinylbenzylphosphonium nitrate)(PTOVBPNO3) membrane electrode demonstrated a selective response to nitrate in the concentration range 5 × 10–5–0.1 mol dm–3, with a slope of –53.4 ± 0.5 mV decade–1. The selectivity of this electrode for nitrate ions can be favourably compared to conventional nitrate ion-selective electrodes based on quaternary ammonium ion-exchange sites. Notably, a significant improvement of selectivity for nitrate by two orders of magnitude was obtained in the presence of perchlorate. The PTOVBPNO3 membrane electrode was used for the determination of nitrate in samples of commercially available fertilizers.

Comparative studies between ion‐selective field effect transistors and ion‐selective electrodes with polymeric membranes

AbstractCharacteristics of ion‐selective field effect transistors (ISFETs) and ion‐selective electrodes (ISEs) with solvent polymeric membranes were compared for slope, selectivity, drift, and hysteresis. Drift and hysteresis of ISFETs were significantly inferior to those of analogous ISEs. Experiments using conventional ISEs with internal electrolyte solutions and ion‐selective liquid membranes of different kinds indicate that both primary ion and ionophore are necessary in the internal electrolyte solution and the ion‐selective membrane, respectively, to achieve small drift and small hysteresis. It is, therefore, concluded that to realize highly reliable membrane‐solid contact devices, the interface between the membrane and the solid in membrane–solid contact devices like ISFETs and coated wire electrodes (CWEs) should be electrochemically defined.

Implications of ion-exchange kinetics on ion-selective electrode responses and selectivities

Simple principles that have been recognized for some time to be important for the description of equilibrium (or pseudoequilibrium) responses of ion-selective electrodes (ISEs) are further developed into a theory that explains their time-dependent responses. Calculations based on the theory provide new insights into how selectivity coefficients may depend upon kinetic as well as thermodynamic parameters. The theory is not confined to conventional ISEs, but also applies to ion-selective field effect transistors (ISFETs) and coated wire electrodes (CWEs) as well

Solvent polymeric membrane ion-selective electrodes

The significant role of poly(vinyl chloride) as a support polymer in solvent polymeric ion-selective electrodes is briefly reviewed. This lays emphasis on the way PVC has contributed to the relatively high state of development of conventional ion-selective electrodes, microelectrodes, coated-wire electrodes and ion-sensitive field effect transistors based on liquid ion-exchanger and neutral carrier ionophore sensors. Also discussed are possibilities of using alternative polymer matrices for overcoming some of the shortfalls of the PVC electrodes.

Microelectronic ion sensors: A critical survey

Microelectronic ion sensors based on monolithic silicon integrated circuit (IC) and hybrid circuit technologies have been the subject of considerable research and development over the past 15 years. This paper reviews the conceptual background and history of both kinds of device, comparing their operation with those of conventional ion-selective electrodes and coated-wire electrodes. Attention is focused on the interfacial processes involved in the ion-sensing mechanism of microelectronic devices, with particular reference to the significance of models based on either ideally blocking or nonblocking mechanisms. This is a matter which has important theoretical and practical consequences for both silicon IC-based microelectronic sensors such as the ionsensitive field-effect transistor (ISFET) and hybrid circuit based devices. Practical problems associated with effective encapsulation and the provision of a suitable reference electrode are also considered.

Development of ion-sensitive field effect transistors for pH and ionic concentration measurement

Ion-sensitive field effect transistors (ISFETS) are miniaturised, semi conductor, chemical sensors which constitute an attractive alternative to conventional ion-selective electrodes. The theory, structure and fabrication process of silicon monolithic ISFET probes designed and manufactured at the S.A. Institute of Technology are briefly described. A number of ISFET probes were activated to respond to specific ions and characterisation experiments have been performed. Sensors for pH, silver, copper and nitrate were produced and tested. Various methods of application of the sensitising materials were employed and in some cases a comparison of methods made. The silicon chip incorporated an ISFET, standard MOS transistor and diode so that a range of circuits could be explored. These included both voltage and current modes of operation with temperture compensation possible. Attention has been given to the provision of an appropriate microelectronic reference element, this being a major problem in all miniature ion-selective sensor.

Electrochemistry of chemically sensitive field effect transistors

Abstract : It is shown that ISFETs are closely related to conventional ion selective electrodes. The time response characteristics of these devices are examined in detail. The possibility of their use as direct charge sensors is critically evaluated. (Author)

Ion-selective Electrodes and Enzyme Electrodes in Environmental and Clinical Studies

Electrodes have been developed for the assay of glucose, urea, amino acids, uric acid, phosphate, nitrate and perchlorate. The electrodes for the organic compounds are enzyme electrodes which are prepared by chemically immobilizing an enzyme over the outside of a conventional ion-selective electrode. These electrodes will be discussed in depth. The progress and the development of the electrodes that show sensitivity and selectivity for phosphate, nitrate and perchlorate will be outlined. The basis of these sensors is a complex of a transition metal of either an analog of thiourea or an organic chelator, such as 1,10-phenanthraline. Such electrodes respond linearly to phosphate, nitrate or perchlorate, and show selectivity over sulphate, halides and acetate. The linear range of all these electrodes is approx. 10(-1)-10(-5) M with a near Nernstian slope and a reproducibility of 1%. The electrodes are stable and can be used continuously.