A rotary evaporation (or rotavap or rotovap) uses precise engineering to effectively remove solvents from a sample using evaporation. Most rotovaps make use of a vacuum and pressure control monitor to precisely control pressure within your system, increasing evaporation efficiency. In many commercial labs, these machines need to be running around-the-clock without fail.
- Pour the mixture of solvent and desired compound in a round bottom flask. Best results are achieved when the flask is filled less than half full of the solution.
- Fill the rotovap cold traps with dry ice.
- Attach a glass “bump trap” which prevents any solution from entering the main part of the rotovap. Secure with a Keck clip.
- With a Keck clip attach the flask and bump trap to the adapter portion of the roto-evaporator.
- Lower the flask into the water bath. This helps to prevent the flask from disconnection.
rotary evaporation Operation
- Start the rotation. Different speeds are preferable for different volumes.
- Slowly start increasing the vacuum. The vacuum is at the proper strength when: 1) condensation of the solvent can be seen on the cold finger or in the receiving flask, or 2) the solvent begins to bubble.
- Turn on the heat for the water bath. Recall from general chemistry that vacuum reduces the boiling point of the solvent, so significantly lower temperature is needed to evaporate the solvent using a rotovap than at STP.
- Adjust the vacuum setting as needed.
- When all solvent has been removed turn off the vacuum and return the flask to atmospheric pressure.
- Stop the rotation.
- Raise the flask from the bath.
- Remove the flask from the adapter.
- If there is more solvent to remove it can be added it to the same flask and the procedure is repeated. Remember to empty the receiving flask when the evaporation is complete.
Application of Rotary evaporation
Rotary evaporation can be used to separate solvent from many organic, inorganic, and polymeric materials. It is crucial that the desired compound has a lower boiling point than the solvent and that the compound does not form an azeotrope with the solvent. If these conditions are true, rotary evaporation may be a very efficient technique to separate solvent from the compound of interest. Lower boiling solvents work best, however, rotary evaporation is commonly used to remove water. Higher boiling solvents such as DMF and DMSO are more easily removed using other techniques such as lyophilization, however, with a very good vacuum pump, they may be removed using rotary evaporation.