Five ways to optimize the pressure values of your rotary evaporation

If you’ve been trying to improve your rotary evaporation process, I do hope this next blog post can take some pressure off your chest. Take a look at some of my suggestions for finding, adjusting or maintaining the best pressure values for the solvent you are trying to evaporate. See how to avoid bumping, foaming and improper pressure settings with a few easy tips.

We paid a lovely visit to my daughter and her husband the other day. My son-in-law is an avid trumpet player. I am rather tone-deaf and have never really attempted to play musical instruments on my own. He got a kick out of explaining to me how to properly blow in the trumpet to produce a sound. And he had a blast (no pun intended) showing how the amount of pressure you apply when you blow changes the sound that you produce. He was very proud of his loud and high tunes, but they did make him quite red in the face. We agreed the optimal pressure applied should both keep him alive and the music produced pleasant to my ears.

Walking back to the lab the next day, I chuckled at how important optimal pressure is in so many everyday life activities and in lab activities! Take rotary evaporation! There are a limited number of parameters you can tweak to improve your process and setting the best pressure values can certainly help you achieve better performance.

In rotary evaporation, we use a vacuum to alter the pressure. Lower pressure reduces the boiling point of the solvent sufficiently enough so that the distillation can be carried out at a lower temperature. This helps save time and energy.

But you need to be careful with how you set the pressure values to avoid unintended consequences, such as bumping, foaming, re-boiling or condenser overloading from using inappropriate pressure values for your solvent and others. So here come five ways to optimize your pressure when performing rotary evaporation:

1. Begin slowly – Gently reduce the pressure to the desired set value to avoid bumping or foaming. You might be tempted to reduce in one quick step to save time, but this will certainly cause you some headaches due to bumping effects. Bumping increases the chances that your solvent is easily sucked into the condenser and your distillate is contaminated. You will have to waste time cleaning your glassware to avoid contamination and to get back the amount of sample that you lost in the condenser. Even more, if your sample is heat sensitive, you risk damaging the solvent.

pressure settings, pressure values, rotary evaporation, laboratory evaporation, rotary evaporator

2. Choose working pressure carefully – I would suggest finding recommended pressure values for the solvent you are trying to evaporate. You can use solvent tables (example of a few solvents below) or use a rotary evaporator with an interface that has a solvent library.

SolventVacuum (in mbar with boiling point of 30°C and heating bath at 50°C)

3. Keep the pressure at constant values – Sudden changes of pressure will either stop the distillation or cause bumping or foaming. A great way to consistently maintain pressure values is to use an interface-controlled system, which greatly reduces pressure fluctuations.

4. Automate the process – Inform yourself about how evolving technology can help you find and maintain pressure values during your distillation even if you don’t know the sample characteristics. For example, an AutoDest sensor is a tool designed to automatically perform distillations of samples, also in cases where you are uncertain of what pressure settings you should select.

5. Use a foam sensor – Foaming and bumping are two of your worst enemies during laboratory evaporation. A foam sensor is a great weapon in your battle against them. The sensor prevents the sample from reaching the condenser by temporary and automatically aerating the evaporation unit.

Now those of you who have some experience with rotary evaporation might notice that I am leaving two points out. Importantly, when setting the pressure values, you need to stay above ambient temperature to avoid re-boiling. You also need to prevent condenser overload by remaining below the 75% line. I would like to dedicate more time to these particular points, so keep checking the blog for more information on these topics.

Hopefully I’ve released some of that pressure to get the pressure values right with these five ideas. If so, that would really be music to my ears, just like those trumpet melodies.

And If you are curious to learn more about other parameters that play a role in optimizing rotary evaporation, then get our free evaporation poster and try the rest of the tips out.

If you’ve been paying close attention, I did mention at the start that pressure plays a main role in many life and lab activities. Let my previous blog posts serve as evidence, as I’ve already talked with you about the positive effect of using pressure gradients during freeze drying and the importance of pressure in condenser overload. And I am more than certain, this is not the last time I will allude to pressure here on the blog. But stick around and hold me true to my word.

Till next time,

The Signature of Bart Denoulet at Bart's Blog