CALCULATION AND CONTROL OF FREE DIVALENT-CATIONS IN SOLUTIONS USED FOR MEMBRANE-FUSION STUDIES

This chapter discusses a computer program that allows the calculation of multiple equilibria between different ligands and metal ions. Although the media prepared according to the calculation generally give concentrations in good agreement with measured values, the calculation should always be controlled. The computer program developed considers nine different ligands—EDTA, EGTA, HEDTA, NTA, ATP, ADP, GTP, phosphate, and creatine phosphate—and corrections for temperature and ionic strength. The program calculates either the total amount of metals to give the desired free metal concentrations (Ca 2+, Mg 2+) or, in the reversed mode, it calculates the free metal concentration for a given total amount of metals and the selected mixture of ligands. Furthermore, an option exists for calculating the apparent association constants under different conditions (pH, T, I), to choose the appropriate ligands for the experimental purposes. For this purpose, an easy and inexpensive procedure for the preparation of ion-selective electrodes is then described. © 1993, Elsevier Inc. All rights reserved.