Rotary evaporator

A rotary evaporator, or rotavap, is a device used in chemical and biochemical laboratories for the efficient and gentle evaporation of solvents. The main components of a rotary evaporator are a vacuum system, consisting of a vacuum pump and a controller, a rotating evaporation flask which can be heated in a heated fluid bath, and a condenser with a condensate collecting flask. The system works because lowering the pressure lowers the boiling point of liquids, including that of the solvent. This allows the solvent to be removed without excessive heating.

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Evaporation under vacuum can be performed in a standard distillation rig. However, the rotary evaporator has a key advantage. As the evaporating flask rotates, the liquids are forced to the outside of the flask with the centrifugal motion. This creates a larger surface area of the liquids and hence allows for quick, gentle evaporation.

Rotary evaporators are highly effective at removing the majority of organic solvents during the extraction process. The remainder of the solvents are usually removed using a high-vacuum line. Rotary evaporators are usually not recommended for removing aqueous solvent due to water's high boiling point.

The key disadvantage with rotary evaporators is the potential for sudden uncontrolled boiling or "bumping" which can result in loss of some portion of the substance intended to be retained. Bumping can be prevented by regulating the strength of the vacuum, by reducing the temperature of the water bath, or by the use of boiling chips. Some rotary evaporators are also fitted with a 'descending condenser' glassware assembly that aids evaporations with bumping tendencies. Scientists who have many samples to evaporate often prefer to use a modern centrifugal evaporator which safely dries samples in parallel and also prevents "bumping" episodes.

The rotary evaporator was invented by Lyman C. Craig^[1], while it was first commercialized by Swiss company Büchi. The Büchi Rotavapor continues to be the most widely used rotary evaporator, and Rotavapor has become a synonym for such instruments. Other manufacturers include IKA, Heidolph, Stuart and EYELA.

The most common form is the benchtop rotary evaporator, though large scale (20L and 50L) versions are available and are used by pilot plants in large pharmaceutical companies.

See also

• Vapor pressure
• Centrifugal evaporator

References

1. ^ Craig, L. C., Gregory, J. D., and Hausmann, W. Versatile laboratory concentration device. Anal. Chem. 22, 1462, (1950).