A Primer On Vacuum Concentration

Vacuum concentration (or centrifugal concentration) has been popular since the 1980s when it became a widespread application for drying plasmid DNA. The early vacuum concentrators were little more than closed centrifuges linked to vacuum pumps, and for the drying of samples in microcentrifuge tubes, such a evaporator design was satisfactory. Since its introduction the applications for vacuum concentrators have expanded dramatically and is now used for analyte concentration and solvent removal in addition to drying.

Vacuum concentration removes one or more solvents from a solution by decreasing the atmospheric pressure over the liquid phase. By reducing the pressure exerted on the liquid phase, solvent molecules more easily enter the gas phase. The same effect is produced by applying heat. The resulting increase in solvent vapor pressure delivers more solvent molecules into the gas phase. Evaporation systems, such as the RapidVap, also work by exploiting the gas phase/liquid phase equilibrium at atmospheric pressure and room temperature. Evaporators pass inert gas over the solvent, thereby removing gas phase solvent molecules. The perturbation of the gas phase/liquid phase equilibrium concentrations results in more liquid phase solvent molecules escaping into the gas phase. In both cases, the result is a loss of solvent and a concentration of non-volatile molecules.