[Determination of partial solubility parameters of lactoses and its application to solubility evaluation]

Partial solubility parameters of lactose packed into a glass column were calculated from adsorption energies of n-decane, acetonitrile and ethyl alcohol determined by gas-solid chromatography. Three kinds of crystalline lactoses, alpha-lactose monohydrate, anhydrous alpha-lactose (desiccated) prepared by desiccation with methyl alcohol, and anhydrous alpha-lactose (heated) prepared by heating, were used. It was characterized from the results that the partial solubility parameter, delta p, due to dipole interaction, of anhydrous forms had two-fold value than that of the hydrous form. In addition, it was suggested that the affinity of lactose for water vapor and the solubility of lactose for water were able to be evaluated using the three dimensional plot of partial solubility parameters and the interaction radius calculated from partial solubility parameters. It was shown that the appropriate information for the evaluation of physicochemical properties of active ingredients and excipients in the formulation study could be obtained from the data determined using partial solubility parameters.