Foam is foe in rotary evaporation. Here is how to prevent it.

Anyone who has ever looked at their flask during laboratory evaporation and noticed the appearance of foam has probably just wanted to scream: “Get the foam out of here.” But rather than dealing with the problem after it arises, why don’t you nip it in the bud and prevent foam from happening altogether? How, you may ask? Read on about two major factors that can prevent foam in your flask: pressure and technology.

The weather has been getting chillier. One of the only nice things about rainy cold fall days is getting into a warm bubble bath. Oh I do love to soak up the heat in there and I want as much foam as possible for the ultimate floating-on-a-cloud experience. You know where I don’t like foam though? In my beer glass. And do you know where I absolutely despise getting foam into? My rotary evaporation flask!

When your sample foams and you do not adapt the vacuum, the foam starts to expand and can end up entering the condenser. Your product then ends up going all over your entire rotary evaporator , rather than staying where it belongs: in the evaporating flask. If you do end up with this problem, you must clean the entire glassware to de-contaminate the system from your product and to re-collect your compound.

If the thought of all this extra work, like me, makes you feel queasy, then let us find out what weapons you have in the fight against foam.

One of the key ways to eliminate this problem is to control the pressure. Pressure is important in rotary evaporation , pressure is important in freeze-drying and pressure is important in foam control.

Pressure during laboratory evaporation is generated by a vacuum , needed to lower the boiling point of the solvent far enough so that the distillation can be carried out at a lower temperature.

To avoid bumping or foaming, you need to gently reduce the pressure to the desired set value.

Once you are operating at the desired pressure, you need to avoid any sudden changes of pressure. These types of fluctuations could cause bumping or stop your distillation altogether. Consider that an interface-controlled system can greatly reduce any such unplanned occurrences. The only way to prevent foam manually is to stay in front of your rotary evaporator the entire time and manually break the vacuum with the stopcock until the problem is solved. As you can image, this could be a rather tedious and time-consuming process.

So let us instead explore what technologies, besides an interface-controlled system, are available to help you combat this challenge.

For one, you could use an integrated solvent library, or at least a solvent table, to look up the recommended values for the solvent you are using. Operating at optimal pressure values helps avoid unexpected situations that could lead to foam formation.

Undoubtedly the most useful device to prevent your sample from foaming into the condenser is the foam sensor. The sensor functions by temporarily aerating the system automatically.

If you’re a true techie and want to enjoy your system completely worry-free, you can combine the foam sensor with an AutoDest sensor. The AutoDest sensor performs automatic distillations with specific settings continuously adjusted by the system. Together, the foam sensor and AutoDest sensor enable unattended automatic distillation, so you can confidently use your time elsewhere.

I hope this post can help you foam-ilate a nice solution to getting rid of foam before it has the chance to disturb your evaporation. If you would like more tips on how to optimize your rotary evaporation, download this free poster . The poster doesn’t address all your questions? Then feel free to drop me a line with what you’d like to see on the blog in the comments section.

Till next time,

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