INTERFERENCE STUDIES ON A PVC-MATRIX MEMBRANE CALCIUM ION-SELECTIVE ELECTRODE BASED ON CALCIUM BIS-DI[4-(1,1,3,3-TETRAMETHYLBUTYL)PHENYL] PHOSPHATE AS SENSOR AND TRI-NORMAL-PENTYL PHOSPHATE AS SOLVENT MEDIATOR

Interference potentials, EM, defined as the difference between the observed potential and the potential calculated assuming that there is no interference, have been determined, and their fit to the equation EM = -(RT/F) 1n [1 + KM aB/(aCa) 1 2z discussed for a PVC-matrix membrane calcium ion-selective electrode based on calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate as sensor with tri-n-pentyl phosphate as solvent mediator in mixed solutions of CaCl2BClx, where B = Li, Na, K, Mg, Zn or Cu, at total ionic strengths of 0.2, 0.4 and 0.6. Generally, KM for the alkali metal ions is considerably less for this electrode than for a comparison electrode based on Orion 92-20-02 liquid ion-exchanger in PVC. Occasionally, the data do not fit the equation. Thus, particularly for the bivalent ions, although the plots of exp[-EMF/RT] vs. aB/(aCa) 1 2z are usually linear, they frequently do not intercept the ordinate at 1.00 and/or may give negative slopes and hence negative KM values. © 1979.