Development of a solid-state thick film calcium ion-selective electrode

Abstract

A solid-state calcium ion-selective electrode was developed using thick film metallization process. Silicone rubber or photoresist was combined with ionophore (ETH 129) forming calcium ion-selective membrane which was coated onto different surfaces of electrode. Super-Nernstian equilibrium relationship between the phase boundary potentials and calcium ion concentrations was observed in the silicone rubber-based membrane that was doped with 10−7M CaCl2 treated montmorillonite. This equilibrium relationship was eliminated when the membrane was doped with 0.1M CaCl2 treated montmorillonite. The use of photoresist simplified the manufacturing process for the membrane. The memory effect of the silicone rubber-based membrane could be eliminated when the membrane was conditioned with 0.1M CaCl2. The response time of the electrode with silicone rubber and montmorillonite modified silicone rubber were less than 20s and the one with photoresist was less than 3min. The sensitivity of these calcium ion-selective electrodes were around 30mV per decade, and the selectivity were in the rang from −2.9 to −3.8 for Na+, K+ and Mg2+ ions based on fixed primary ion method (FPIM).