Infinite dilution activity coefficients are a valuable tool in separation process design. They are used as a direct indication of unlike pair interactions; they are often relatively straightforward to measure or estimate; and their application can frequently save extensive experimental or computational effort. The initial development of the MOSCED equation was limited by the inadequacy of scales of acidity-basicity available at the time, resulting in a large number of adjustable parameters. Recently, spectroscopic and other physico-chemical data have become available that can be used to improve greatly the quantitative estimation of the various molecular interactions in solution. One such set of spectroscopic data that provide an accurate and easily obtainable measure of the acid-base interactions in solution is the solvatochromic acidity/basicity scale. We have used this extensive database to evaluate the chemical interaction term in the MOSCED model, and substantially reduce the number of adjustable parameters with no significant change in accuracy. The results may lead to a much better basic understanding of solution interactions.