ABSTRACT
Solubility is defined here as the concentration of the solute in a solution when equilib rium exists between the pure solute phase and the solution phase. Knowledge of solubil ities can be critical in formulating products, developing analytical methods, and evalu ating drug transport or distribution problems. The approaches presented in this chapter are ideal solution theory, regular solution theory, and the Hansen solubility approach. Of these three, the only one that was developed to describe solutions involving polar species was the Hansen approach. As the reader will discover, however, the Hansen approach is principally based on regular solution theory, which, in turn, was derived from ideal solu tion theory. Thus, one cannot consider the Hansen solubility approach without some background in the previous theoretical discussions of solubility behavior.
