The objective of this work was to control and monitor the solvent extraction process of gold chloride by tri-butyl phosphate (TBP) through measuring Oxidation Reduction Potential (ORP). The results effectively indicate the application of ORP measurement approach in on-line monitoring/controlling the process of gold chloride solvent extraction. This approach showed that any decrease in gold extraction leads to an increase in OR? value. Based on this finding and by applying the slope analysis method, it was proved that Au tetrachloride is the predominant anion in aqueous phase and each mole of Au is absorbed by three moles of TBP. Considering the fact that a variety of ions are extracted from aqueous media in solvent extraction process a new equilibrium would be created. On the basis of Nernst equation, the electrochemical potential of system is changed. This research aims at anticipating the kind and concentration of ionic species based on the potential value of solution. (C) 2015 Published by Elsevier Ltd.