Construction of all-solid-state ion-selective sensors using electrolyte-containing polymers

All-solid-state NO₃^-, K⁺, NH₄⁺, Na⁺, and Ca²⁺ ion-selective sensors (ISEs) were prepared using polyvinyl butyral (S-LEC®K KX-5). In the present case, polyvinyl butyral was used as a porous material to keep the internal solution of the respective ISE. All sensors exhibited near-Nernst responses in the concentration region between approximately 10^-5 and 0.1 mol dm^-3. To avoid the influence of KCl as interfering ions, MgSO₄ was used as an electrolyte within the salt bridge. Although the liquid junction potential was generated, the potential difference was stabilized within about few minutes. The NO₃^--ISE showed high stability with no potential drift during 12 h of continuous measurements and maintained high sensitivity even after 3 weeks of storage in ultrapure water. Solidification of the internal solution is expected to make the sensor smaller and increase its mechanical strength. As an actual measurement, the sodium concentration in plasma samples using the Na⁺-ISE was measured to confirm agreement with literature values.