What Is Purification by Sublimation?

Purification by sublimation is a chemical process used to separate nonvolatile impurities from volatile compounds. The process of sublimation involves heating an organic compound so that it goes from a solid phase to a gaseous or vapor state without going through the liquid phase, states the University of Arizona.

The technique requires using a flame as the heating element and special sublimation equipment that consists of a cold surface test tube filled with cold water. This sublimation process can be useful for the purification of organic compounds, such as camphor, salicylic acid and benzoic acid. However, the process is utilized when the compound has nonvolatile impurities. Sublimation purification is also a process used to separate nonvolatile impurities from crude caffeine, states Khan Academy. By using this technique, gaseous caffeine and crystal caffeine are formed.