Common Physical Techniques used in Purification

This chapter discusses the methods used in the purification of reagents and solvents. More than one method of purification may need to be implemented to obtain compounds of highest purity. Common methods of purification are solvent extraction and distribution, distillation, recrystallization, sublimation, and chromatography. Extraction of a substance from suspension or solution into another solvent can sometimes be used as a purification process. One of the most widely applicable and most commonly used methods of purification of liquids or low melting solids (especially of organic chemicals) is fractional distillation at atmospheric, or some lower, pressure. This method can be assumed to be suitable for all organic liquids and most of the low-melting organic solids. Recrystallization is the most commonly used procedure for the purification of a solid material. Sublimation differs from ordinary distillation because the vapor condenses to a solid instead of a liquid. This procedure has the added advantage of removing occluded solvent used in recrystallizing the solid. Chromatography is often used with advantage for the purification of small amounts of complex organic mixtures. Chromatography techniques rely on the differential distribution of the various components in a mixture between the mobile phase and the stationary phase.