Individual Activity of Calcium Ions in Pure Solutions of CaCl(2) and in Mixtures

Individual ion activities were calculated for Ca(2+) in pure solutions of CaCl(2) and in mixtures of CaCl(2) with MgCl(2) and with NaCl, using different conventions to obtain γ(Ca2+). The results were compared with potentiometric measurements, using calcium specific electrodes. It is found that significant differences should be obtained for emf's using the different conventions, when ionic strength is greater than 0.5. The experimental results obtained for ionic strengths up to 0.2 favor slightly the direct use of γ(±CaCl(2)), but are fairly consistent also with the use of the Guggenheim and the MacInnes conventions

Fabrication and Evaluation of Membranes as Specific Electrodes for Calcium ions

Membranes fabricated from an inert polyvinyl chloride matrix impregnated with tributyl phosphate and with tributyl phosphate plus thenoyl trifluoroacetone were tested as electrodes specific for calcium ions. Both types of membrane exhibited a high specificity for calcium ions in the presence of sodium, magnesium, and barium ions. In the presence of perturbing ions, the usefulness of membranes is limited by both the transport of current and development of potentials by the interfering ion. An experimental method for evaluating these interfering quantities is presented