Solubility and Extractability in the Pharmaceutical Sciences: A Practical Exercise with Pure Compounds

The extractability of pure organic compounds is a ubiquitous concept in the pharmaceutical field. During this laboratory session, each student receives one vial containing an unknown compound. For this sample, they will determine its solubility in an organic solvent, in water, and then its extractability profile by three liquid–liquid extractions at different pH values followed by the evaporation of the organic phase and the quantification of the residue by gravimetric analysis. The data obtained will allow students to draw a curve representing the acid/base and the hydro- and lipophilic character of their given compound. Once the first part of the session is finished, the students who have tested the same compound share the results obtained. These pooled results will show that the sigmoidal-like curve of the lipophilic acid and its conjugate base or the lipophilic base and its conjugate acid have the same shape, although the solubility in organic solvent and water is different. Lipophilic amphoteric and neutral compounds are also tested in the same laboratory session. This exercise with pure compounds will allow students to identify the physicochemical characteristics of organic compounds and anticipate the separation of such compounds in a mixture.