SELECTIVITY COEFFICIENTS FOR ION-SELECTIVE ELECTRODES - RECOMMENDED METHODS FOR REPORTING K-A,B(POT) VALUES - (TECHNICAL REPORT)

The limitations of the Nicolsky-Eisenman (N-E) equation for the determination of potentiometric selectivity coefficients, K-A,B(pot),critically evaluated int terms of K(A,B)(pot)ons of unequal charge, non-Nernstian behavior of interfering ions, and activity dependence of K-A,B(pot).for the activity dependence of K(A,B)(pot)qualities of values depending on the method employed were thus elucidated. Also, when ions of different charge were involved, K-A,B(pot) values obtained found to be either unrealistically large or small depending on whether the ion of higher charge was considered as a primary or an interfering ion. On the basis of these considerations, new approaches including the matched potential method, a method independent of the N-E equation, were recommended for the determination of K-A,B(pot).