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-mu-l and make full use of the small ion-sensing probe, we constructed a miniature cation-exchange separation column (support 10-mu-m polystyrene) with a PTFE tube (20 mm x 1.5 mm I.D. x 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.