In this paper, we present the general equations for a model of ion transfer reactions across the oillwater interface assisted by a neutral protonatable ligand. Our analysis is mainly focused on the effect of water autoprotolysis. The equations reported in this paper allow us to simulate the system under all possible conditions. Three different models are compared: buffered solutions (BASA model), unbuffered solutions considering and not considering water autoprotolysis (UBASA and UBAS model, respectively). (c) 2005 Elsevier B.V. All rights reserved.