Mar 21 2019
Extremely increased levels of contaminations on the surface of magnetic stir bars bypass periodic cleaning and carry highly reactive traces of metal types from previous experiments to the following ones.
Typical example of magnetic stir bars in a chemistry lab: surface changes are clearly observable. (Image credit: Evgeniy O. Pentsak)
Electron microscopy experiments and DFT calculations were used to demonstrate that the plastic surface of magnetic stir bars can create reactive centers, leading to absorption of metal atoms from solution followed by the growth of metal nanoparticles. This process easily occurs on the surface of magnetic stir bars coated with polytetrafluoroethylene (PTFE) and is globally used in advanced biology and chemistry laboratories.
Many metal nanoparticles are present on the surface of the conventional magnetic stir bars. The existence of an already used magnetic stir bar in reaction medium has been shown to be adequate for commencing a wide-ranging catalytic reaction (advanced by draining of metal species from the PTFE surface).
Magnetic stir bars are often considered as reusable consumables and remain for years in many laboratories. It has been shown by this study that in a regular catalysis laboratory, nearly all magnetic stir bars eventually become permanently contaminated with metal nanoparticles after use for about one week. Such impurity cannot be completely removed by standard routine cleaning procedures. Certainly, subsequent release of traces of metal in the following reactions is not acceptable even in small amounts, since it may influence various experimental settings.
The authors of this study investigated stir bars from different laboratories. Of the 60 bars, only 1 was found to be clean. Further investigation of the sources of contamination was carried out by online monitoring of the contamination process with ESI-MS. Researchers have also shown the impact of contamination on catalysis.
Metal contamination, which is of great significance in the development of high-performance synthetic and catalytic systems, is a crucial problem. Although many problems regarding metal contamination have been reported in previous studies, the chemical reactivity of PTFE has not been explored, as it was considered as an inert material.
There has been no article to attract great interest from any chemist or biochemist for perusal, but this study is intriguing. Magnetic stirrers are highly essential in the treatment of solutions. In the research community, chemical activity and easy contamination of stir bars are similar to a bombshell.