Generalized theory for two-phase ion-pair and complexometric titrations. I. Two-phase titrations without side reactions.

A systematic theoretical treatment of the two-phase titration based on ion-pair and metal-complex formation is presented. Equations for the titration curve, accuracy, equivalence point and choice of the indicator are derived. Much attention is paid to the parameters determining the 'titratability' viz. extraction constant, distribution constant, phase volume ratio and the concentration of the analyte. Special attention is given to the role of intermediate ion-pair and metal-complex formation in the aqueous phase. The ion-pair formation in aqueous solution is examined closer by means of the relationship between the association constant in water, the degree of dissociation of the ion pair (alpha) and the concentration of the counter ion. The merits of this theoretical treatment are illustrated with literature examples.