How to Prevent Foam Formation and Bumping in your Rotary Evaporator

It is a common occurrence for samples being evaporated in a rotary evaporator to foam up, or starting bumping. This usually leads to sample loss, and possibly contamination. Foaming occurs when the sample’s surface tension decreases, leading to the production of bubbles. Bumping however refers to the sudden and vigorous release of vapor bubbles from the liquid phase, which can result in the sample splattering or even ejecting from the evaporator flask. Both situations can be problematic as they may lead to sample loss, reduced efficiency, or potential hazards. In this blog post, we’ll discuss a few steps you can take to mitigate the risk of foaming and bumping.


Reduce your sample’s concentration:

Foaming can occur if your sample is too concentrated. Diluting it with an appropriate solvent can help reduce foaming tendencies.


Adjust the vacuum pressure:

Lowering the vacuum pressure can significantly decrease the risk of bumping. You’ll want to ensure that the vacuum level is set correctly based on the sample’s boiling point to maintain a controlled evaporation process. As a rule of thumb, you’ll want to go slow by starting with  little vacuum, and gradually decreasing the pressure while visually inspecting your sample to make sure no bumping occurs.


Use an appropriate flask size:

Make sure that the flask size you’re using can comfortably fit your sample. This will prevent both foaming and bumping. You want to avoid overfilling your flask.


Use anti-bumping agents:

Glass beads and boiling chips can provide your sample with a nucleation site for bubble formation which ultimately reduces the risk of bumping.


Control the heating rate:

Just like the vacuum pressure, you want to keep a tight control of the heating rate of your sample. Gradually increase the temperature to avoid the  formation of large bubbles. A slower, more controlled heating process promotes gentle evaporation.


Optimize solvent selection:

Different  solvents have varying tendencies to foam or bump. Selecting a solvent with lower foaming characteristics or employing an appropriate solvent mixture can mitigate these issues.


Use Personal Protective Equipment (PPE):

As always, safety first! Even if you follow all the aforementioned steps, surprises still happen. Make sure to don your lab coat, gloves, and safety goggles to protect yourself in case of splattering or sample ejection.


There you have it! Next time you use your rotary evaporator, make sure to follow these steps for a foaming-free bumping-free process. Stay tuned for more!