Rotary evaporator is an ideal instrument necessary for the concentration, drying and recycling relied on by the chemical industry, pharmaceutical industry, foods, environmental protection, universities and colleges, and research laboratories and so on, and especially adaptable to the small scale production unit.
Procedure of operation a rotary evaporator
- 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.
2. Rotary Evaporator 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.
Tips and Tricks
Distilled water should be used in the heating bath to minimize the scale build up in the bath which coats the thermistor and heating coils. It is very difficult to remove and reduces the efficiency of the bath. In addition, regular tap water will promote the growth of spectacularly disgusting algae colonies, particularly during the summer months. The best protocol is a regular exchange of the water.
To remove algae gunk from the inside of a coiled water condenser, the condenser has to be removed from the rotavap and the coil is soaked in a dilute nitric acid solution for a few hours. After carefully rinsing the insides, the rotavap is reassembled. All standard safety precautions should be followed when working with nitric acid!
The ground glass joint holding the flask does not need to be greased, but on rare occasions it (or the bump bulb) may get “frozen”. Some companies sell special joint clips that can free frozen joints simply by screwing them in one direction. If you are not lucky enough to have these and cannot release the joint you probably want to ask your teaching assistant for advice.
If a mechanical pump is used instead of an aspirator to produce a vacuum, a secondary trap has to be used to prevent that the solvent destroys the membrane or is absorbed in the oil.