The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, in Stuttgart, Germany, recently highlighted the work of scientist Gabriele Beck-Schwadorf and her research team, who developed a new analytical method to identify nanoparticles in media such as sunscreens.
This work follows the labeling requirement mandated in July 2013 by the EU Directive on cosmetics and body care products. The mandate states that if nano-sized ingredients are used in a product, the manufacturer must make this fact clear by adding “nano-” to the listed ingredient name. However, according to the institute, it is difficult to prove that nanoparticles are in lotions and other products, thus new analytical methods are needed.
“The light diffusion process and microscopy are not selective enough for [many] studies, including toxicological examinations,” said Beck-Schwadorf, in a press statement. Her team instead refined an existing method to enable them to differentiate titanium nanoparticles within complex media; their approach uses single-particle, inductively coupled plasma mass-spectrometry (or SP-ICP-MS).
“With this method, I determine mass. Titanium has an atomic mass of 48 AMUs (atomic mass units). If I set the spectrometer to that, then I can target the measurement of titanium,” explained Katrin Sommer, food chemist at IGB, in the press statement.
According to the institute, a suspension containing both large and small particles in a non-homogeneous distribution is sprayed into hot plasma. This suspension is thinned out so that individual titanium dioxide particles can be detected and analyzed. Ions are formed from these particles in the plasma and detected by the spectrometer as an ion cloud. The particles are then counted at a speed of ~ 3 msec, and signal intensity correlates to particle size.
The intensity is converted into nanometers and at the same time, particle signals are counted, from which the particle concentration is calculated with up to ten percent accuracy. This establishes how many particles are of a specific size. According to the institute, compared with existing methods, SP-ICP-MS can detect at limits down to ultra-trace amounts—below ppm. It also is fast; examining a product sample of a few milliliters in just ~ 6 min.
