Formation of natural pH gradients in sequential moving boundary systems with solvent counterions. I. Theory

The moving boundary theory has been applied to the special case in which the proton and hydroxyl ion are the sole counterions. Moving boundaries between two monovalent weak acids, two biprotic acidic ampholytes, two weak bases and two biprotic basic ampholytes were considered. This application of the theory leads to constituent concentration relationships, values for pH and conductance of each phase and step pH gradients when sequential moving boundaries are considered. In addition, rigorous conditions for achieving the steady‐state in such systems are also presented. Application of the theory allows for the prediction of the formation and displacement of pH gradients. In contrast to the classical theory of pH gradients formed by ampholytes, the establishment of inverse pH gradients and the electrophoretic displacement of natural pH gradients is clearly accounted for.