A rotary evaporator is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. The process of rotary evaporation is most often used to separate solvents with low boiling points, such a n-hexane or ethyl acetate, from compounds which are solid at room temperature and pressure. However, careful application also allows for the removal of a solvent from a sample containing a liquid compound, if there is minimal co-evaporation (azeotropic behavior) and a sufficient difference in boiling points at the chosen temperature and reduced pressure.
Example: The following table illustrates a variety of substances, ordered by increasing vapor pressure (in absolute units).
This guide gives basic quick start instructions for rotovaps. It is intended to provide a starting point for learning the process. Parameters should be adjusted to suit specific needs.
- Clean and assemble unit. Make sure all pieces are cleaned and sterilized using an alcohol solution.
- Connect chiller to condenser and set to 0C (32F). Always fill a rotovap condenser from the top down (chiller output to top of condenser, chiller input to bottom of condenser).
- Connect vacuum pump to cold trap and connect cold trap to vacuum port on rotovap.
- Turn on heat bath and set to 40C (113F).
- Once heat bath, chiller and cold trap have reached desired temperatures, turn on rotovap motor and set speed to approximately 100 RPM (does not have to be precise). Keep in mind, higher RPM’s will increase evaporation power but also increase heat load.
- Start vacuum pump and allow vacuum to pull down for a few minutes before injection.
- Once vacuum has been pulled to a sufficient level (does not have to be precise but should be below 100 Torr), using the injection valve, very slowly inject approximately 500 mL of solution into evaporating flask and then close the valve. Allow this small amount to begin evaporating. You may see the chiller begin to rise in temperature, this is called “priming” the rotovap.
- Once the temperature stops rising or all liquid is almost completely evaporated, open the injection valve again very slowly so that a small amount of liquid begins to enter the evaporating flask. Do not close injection valve this time but continue to allow solution to enter the evaporating flask.
- At this point you must try to match the input speed to the output speed. What this means is that you should be injecting the same amount of liquid into the rotovap that is equal to the amount of liquid dripping from the condenser into the receiving flask. You will know that the input speed and output speed are matched because the chiller will remain at a stable temperature. If the chiller begins to rise, then you are injecting too much liquid. Dial back the valve until the chiller stabilizes.
- Once everything is stabilized, you may walk away from the rotovap if necessary. Check every so often to make sure temperatures remain stable and evaporation continues efficiently.