SL2 TYPE PHASE SOLUBILITY DIAGRAMS, COMPLEX-FORMATION AND CHEMICAL SPECIATION OF SOLUBLE SPECIES

A method is presented for the analysis of SL2-type phase solubility di agrams. The method allows the determination of individual complex form ation and solubility product constants through rigorous fitting of all segments of the diagram: the rising portion, the plateau and the desc ending portion. Rigorous analysis of the descending portion offers the means of discerning the type of complex precipitate (SL or SL2). The method has been tested by computer simulation of experimental data for both SL and SL2 complex precipitates. The limits of precision of expe rimental data required to obtain reasonable estimates of equilibrium c onstants have been explored through superimposition of statistical ran dom noise. The method has also been successfully applied to the analys is of some experimentally measured phase solubility diagrams that have been reported in the literature. These include the measured solubilit ies of 1,3-dimethylbenzoylurea (DMBU) against catechol concentration i n carbon tetrachloride, tolbutamide (Tolb) against aqueous beta-cyclod extrin concentration, spironolactone (SP) against aqueous gamma-cyclod extrin concentration, in addition to methylparaben, ethylparaben and p ropylparaben against aqueous alpha-cyclodextrin concentration at 25 de grees C.