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

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 10−7 M CaCl2 treated montmorillonite. This equilibrium relationship was eliminated when the membrane was doped with 0.1 M 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 0.1 M CaCl2. The response time of the electrode with silicone rubber and montmorillonite modified silicone rubber were less than 20 s and the one with photoresist was less than 3 min. The sensitivity of these calcium ion-selective electrodes were around 30 mV 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).