Why you should avoid grease in your rotavapor with a PTFE Stopcock

Greasy fries, pizza, hair, rotavapor? No thanks. Keep that stuff off my body parts, my clothes and my lab equipment. Grease in your rotary evaporator is not only unpleasant, it is potentially very damaging to your results. In this post, I tell you all about the dangers of grease and present you with the PTFE stopcock as a great accessory to avoid it from entering your rotary evaporation system.

My nephew is now almost a teenager and he has discovered the gel jar. I mean, the kid uses so much stuff, he could definitely take on a leading role in “Grease”. Or break someone’s face with his hair. It just got me thinking that grease is generally best to be avoided, unless you have screeching doors, an old bike chain or you want to deep fry some donuts.

By the way, you caught me, I am still stuck on the hair topic, as my last post was about hair dye and concentration of natural products !

But back to this greasy topic.

Whenever you perform rotary evaporation , if you have greased your stopcock, grease can enter your system and cause you serious headaches. Grease can enter your reaction whenever you aerate the rotary evaporation system, through backfeeding or when transferring fluids from the receiving or evaporating flask.

You might think this is not a big deal, but it is. Organic solvents, which we commonly evaporate, readily dissolve silicone-based grease, causing it to end up in the product. Sure, polar solvents, such as THF, diethyl ether, DME or dioxane are less likely to dissolve grease, but non-polar hydrocarbon solvents, such as pentane, hexane and petroleum ether and halogenated solvents, such as DCM readily dissolve grease.

Grease in your system is then problematic due to several reasons.
– Grease leads to cross contamination,
– Grease leads to additional peaks at analytics
– Grease cause problems whenever extremely fine chemicals are required
– Machine-grade grease is prohibited if you are working on applications involving food or beverages

So what can you do if you want to improve the vacuum and the handling?

Check the compatibility of your solvent with grease, check if you can use hydrocarbon or fluorether-based, rather than silicone-based grease or, in my opinion best of all, grab a PTFE stopcock!

A PTFE stopcock is a hand-operated valve with a piercing on either side. The part is used to regulate the flow of gases or liquids into the rotary evaporation system . When the handle points in your direction, the valve is fully closed, when the handle points towards the benchtop/floor, the valve is fully open.

The stem and ports of the stopcock are made from polytetrafluoroethylene, commonly known as PTFE or Teflon®. This is an inert, durable, sintered polymer that is resistant to corrosive media. The material of a PTFE stopcock is also FDA-approved, so it is perfectly suitable for production of food and beverages.

A PTFE stopcock is a better alternative than glass stopcocks, since PTFE stopcocks do not streak, they are easier to clean and offer better vacuum without the need to grease. And again, avoiding grease, means eliminating contamination in your solvent.

If you think a PTFE stopcock might be useful for your rotary evaporation system , then take a look at this short video on instructions on how to install it:

Typically, all you need to do to install the stopcock is:
1. Insert the stopcock and set the vacuum (50 mbar)
2. When you are close to reaching the set vacuum value, turn the stopcock three times at 360⁰C
3. The system is now tight and ready to use

So I hope you have your PTFE stopcock all cocked and ready to go! If any concerns are stopping you in your tracks, do drop a line in the comments and I can try to grease them away. But let’s just keep the grease to the comments section!

Till next time,

The Signature of Bart Denoulet at Bart's Blog