Ion-sensitive field effect transistor as a monovalent cation detector for ion chromatography and its application to the measurement of Na⁺ and K⁺ concentrations in serum

An ion-sensitive field effect transistor, which is a small potentiometric ion-sensing probe, was applied as a detector in the ion chromatography of alkali-metal cations. The cation-sensing transistor was prepared by coating the gate part of the probe to form a poly(vinyl chloride) matrix membrane containing tetranactin, which enables detection of alkali-metal ions such as Na⁺, K⁺, Rb⁺, and Cs⁺. To be able to analyse amounts less than 1 μl and make full use of the small ion-sensing probe, we constructed a miniature cation-exchange separation column (support 10 μm polystyrene) with a PTFE tube (20 mm × 1.5 mm I.D. × 2.1 mm O.D.). As an application of the system, Na⁺ and K⁺ concentrations in serum were determined. The analytical results for these two cations were good agreement with those obtained by flame photometry.