A Simple Dynamic Diffusion Model of the Response of Highly Selective Electrodes: The Effect of Simulation Parameters and Boundary Conditions on the Results of Calculations

For a tetrabutylammonium-selective electrode with a ion-exchange membrane, in the real-work scenario corresponding to the determination of selectivity coefficients by the IUPAC-recommended method of separate solutions, it is shown that of the results of calculations obtained within the framework of the dynamic diffusion model based on the use of the finite-difference technique substantially depend on of the chosen boundary conditions and the values of arbitrarily set simulation parameters. The key parameter that determines the quality of simulation results is the thickness of the elementary layer in the membrane phase, especially for low diffusion coefficients. It is found that the use of thin elementary layers in membranes and thick elementary layers in the aqueous phase makes it possible to combine the high quality with the high calculation rate. In simulating the long-term experiments, account should be taken of the accumulation of the potential-determining ion in the aqueous solution volume as a result of its displacement by a foreign ion from the membrane. A good correspondence between calculation data and experimental results is demonstrated.