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Research

Bakker, E.; Buhlmann, P.; Pretsch, E. Chem. Rev. 1997, 97, 3083-3132

(312 cited publications cited this review by August 2003)

I. Introduction

Over the past 30 years, the application of carrier-based ion-selective electrodes (ISEs) has evolved to a well established routine analytical technique. The College of American Pathologists Comprehensive Chemistry Survey in 1980, for example, showed only 22% of the participating laboratories as making potentiometric Na+ or K+ measurements. Already in 1991, on the other hand, the Chemistry Survey listed 96% of 6041 participating laboratories as using Na+ ISE analyzers and only 4% as using flame atomic emission spectrometry. It was estimated that in the USA about 200 million clinical assays of K+ are made every year with valinomycin-based ISEs. 3 Since several other biologically relevant ions are also monitored with solvent polymeric membrane electrodes, it can be safely stated that yearly well over a billion ISE measurements are performed world-wide in clinical laboratories alone. Moreover, ISEs are also utilized in many other fields including physiology, process control, and environmental analysis. They thus form one of the most important groups of chemical sensors. The analytes for which carrier-based ISEs and their counterparts with optical detection have been developed so far are shown in Table 1 and will be discussed in Part 2 of this review. The key components of both types of sensors are lipophilic complexing agents capable of reversibly binding ions. They are usually called ionophores or ion carriers. The latter name reflects the fact that these compounds also catalyze ion transport across hydrophobic membranes. As it will be shown here, their implementation in ion-selective electrodes or optodes is today straightforward.

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