PTFE Stir Bars Can Affect Lab Experiment Results


Scientists at William Marsh Rice University Texas found out that stir bars made of PTFE can skew scientific researches and experiments / Photo by: Ruhrfisch via Wikimedia Commons


Scientists at William Marsh Rice University in Texas found that stir bars made of PTFE can skew scientific lab experiments and studies.

Using PTFE-based stir bars can lead to errors in a standard lab reaction used to control carbon or boron-nitride nanotubes properties. According to, stir bars are pellet-like rods made of ferromagnetic metal and covered in PTFE placed in the bottom of a beaker and spun via a rotating magnetic field. This instrument helps in mixing a solution within a closed flask and without the need for manual stirring.

The Rice lab of Angel Martí released a study, published in the journal American Chemical Society Omega, that explained the events when PTFE stir bars are used to functionalize nanotubes via Billups-Birch reduction. The said technique is a long-used reaction that releases electrons for it to bind with other atoms.

A reduction is usually used to make nanotubes meeker to functionalization—the modifying process for nanotubes applications by adding molecules like proteins. Functionalization can be done simply by spreading nanotubes in a chemical bath infused with the desired molecules. The researchers said Billups-Birch is a one-step method employed to functionalize nanotubes in various molecules. reported that when the Billups-Burch method was used to manipulate nanotubes of boron-nitride, the scientists were shocked to see the tubes turn gray while the PTFE stir bars became black. It added that standard thermogravimetric analysis, typically enough to observe evidence of functionalization, did not see anything out of the ordinary, but the team did.

"Aside from that, we couldn't get consistent results," Martí said. "Sometimes we would get very high functionalization—or apparent functionalization—and sometimes we wouldn't. That was really strange."

Moreover, they found the lithium within the ammonia-based solvent used in the one-step method reaction reacted with the white PTFE from the bars, which turned them black.

Martí said since the carbon nanotubes were black, it would be fair to believe that nanotubes were emitting on the bars throughout the reaction. However, this is not what happens, he added, as they found that the PTFE reacts in the Billups-Birch method.

"Teflon (PTFE) doesn't generally react with anything," the chemist explained, adding, "That's why it's used in stir bars, and in cookware. That's why it's also easy to overlook what we saw happening in the lab."