The Rotary Evaporator

A glass-blower by trade, Walter Buchi made a name for himself when he released his rotary evaporator in the late nineteen-fifties. Scientists C.C. Draig and M.E. Volk were pioneers in developing the modern-day concept, but Buchi developed the first manufactured rotary evaporator, patented in 1957.

A rotary evaporator (often called a “rotovap” by scientists) is a device by which solvents can be removed from reaction mixtures via evaporation. Put very simply, a liquid mixture is heated, and the solvent evaporates and gets collected.

A vacuum is a key component of this device, and is used to aid in the evaporation of the solvent. A vacuum will lower the air pressure in the space above a liquid, thereby lowering the boiling point of the liquid being heated. Often the mixture is very sensitive and highly reactive so excessive heating would not be ideal. The vacuum allows the user to temporarily alter the physical properties of the sample so that solvents can be extracted from a variety of mixtures that would otherwise be impossible. The simplest type of vacuum used on a rotary evaporator is a water aspirator. Picture a tube that is wider at the top and narrows as it goes down, with an opening at the side. When water is channeled downwards, it increases speed, and the pressure is lowered - creating a vacuum effect through the opening at the side. A more complex method would involve a regulated mechanical vacuum pump.

Rotation is not absolutely necessary for the evaporation process to take place. However, the centrifugal forces allow the solvent to rise and be spread thinly over a larger surface, which make sit easier to extract. Also, the rotation helps reduce “bumping.” Bumping is what happens when two substances come together, like water and ethanol, and the total amount is reduced. (This is due the difference in the size of the molecules. For example, if you took one cup of grapes and combined it with one cup of apples, the result would be less than the assumed two cups, because the grapes would fill in the space left by the apples.)

The rotary evaporator has evolved over the years to become more and more advanced, and while features and capabilities of different models vary widely, modern rotary evaporators still consist of seven primary components:

•   The motor that rotates the sample (contained in either a flask or vial)

•   Hot water bath to heat the sample

•   The vacuum used to lower the pressure

•   A vapor duct to capture the solvent

•   Condenser that cools the solvent

•   Flask to collect the solvent after it condenses

•   A mechanism to quickly remove the sample from the hot water bath

The name Buchi now represents a corporation run in part by descendants of Walter Buchi. Buchi develops, produces, and distributes laboratory equipment and analytical instruments for R&D laboratories, as well as for quality control. They support chemical, pharmaceutical and food industries worldwide. Today, the <a href="http://www.capitolscientific.com/buchi_rotary_evaporators.aspx">Buchi Rotavapor</a> continues to be the most widely used rotary evaporator used by research laboratories around the world.