Magnetic stir bars carry 'memory' from previous flasks and tubes

Magnetic stir bars are regarded as reusable consumables, and in many labs they last for months. This study shows that in a regular catalysis lab almost all magnetic stir bars become permanently contaminated with metal nanoparticles. Regular cleaning procedures do not remove such contamination completely. Indeed, subsequent release of metal traces in the next reactions is unacceptable even in small quantitates. The results of this study are published in ACS Catalysis.