The acid dissociation constant (pKa) is among the most frequently used physicochemical parameters, and its determination is of interest to a wide range of research fields. We present a brief introduction on the conceptual development of pKa as a physical parameter and its relationship to the concept of the pH of a solution. This is followed by a general summary of the historical development and current state of the techniques of pKa determination and an attempt to develop insight into future developments. Fourteen methods of determining the acid dissociation constant are placed in context and are critically evaluated to make a fair comparison and to determine their applications in modern chemistry. Additionally, we have studied these techniques in light of present trends in science and technology and attempt to determine how these trends might affect future developments in the field.

An empirical expression was derived for the actual mobility, ix, valid in an extended range of ionic strength, I, between 0.001 and 0.1 mol/1, using a three-parameter exponential fit for the ratio of actual and absolute mobilities (ix0 at I = 0), which consists of two variables: ionic strength of the buffer and charge number, z, of the solute. The charge numbers of the solute anions (21 aromatic sulfonates) ranged between 1 and 6, and the ionic strength was varied in the range mentioned using a sodium acetate buffer. The mobilities were determined at 25.0°C in a coated capillary with suppressed electroosmotic flow. The resulting fitting equation, valid under these conditions, is ix/ix0 = exp(-0.77X zz/). The difference between measured mobilities and mobilities calculated from a tenfold higher or lower ionic strength, using this equation, is within 5% for all experiments. For multivalent ions, ix values can be derived from ixo with comparable accuracy.

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