This can benefit the cosmetics industry using the particle analysis for quality assurance of sun protection and body care products, as well as other consumer goods.
Cosmetics increasingly contain nanoparticles, with titanium dioxide being commonly used in sunscreens to provide UV protection.
There have been fears over the health and environmental risks of nanoparticles which meant a labelling requirement has been in force since July 2013, based on an EU Directive on cosmetics and body care products.
It 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. This means the need for analysis methods is huge, and Fraunhofer says this new method will be a great help.
Process
Electron microscope imaging processes based on the properties of light dispersion are currently used to detect all particles present in a formulation; however Fraunhofer says that they do not differentiate between a cell, a nanoparticle, or a piece of lint.
“The light diffusion process and microscopy are not selective enough for a lot of studies, including toxicological examinations,” says Gabriele Beck-Schwadorf, scientist at the Fraunhofer Institute for Interfacial Engineering and Thin Films IGB in Stuttgart.
The group manager and her team have advanced and refined an existing measurement method in a way that allows them to determine titanium nanoparticles within complex media consisting of several different components that are highly sensitive and delicate.
This method sees researchers measure individual particles by ‘single particle, inductively coupled plasma mass spectroscopy’ (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,” explains Katrin Sommer, food chemist at IGB.
With particle measurement, a suspension is sprayed into the plasma that contains both large and small particles in non-homogeneous distribution.
The suspension has to be thinned out sharply so that one titanium dioxide particle after another can be detected and analysed
“We convert the intensity into nanometers. At the same time, we count particle signals, from which we calculate particle concentration with up to ten percent accuracy. We can establish exactly how many particles are of a specific size,” says Sommers, explaining the procedure.
“The process is generally suitable for complex media, and can also be applied to sunscreen lotions.”
The data analysis and data processing is also performed without specialized software which speeds up the process too as one sample of just a few millilitres can be examined in about six minutes, adds Sommers.
“We have statistically evaluated the raw data using a standard computer program, and thus can work irrespective of the producer. Compared to existing methods, SP-ICP-MS involves a rapid process that uses detection limits that extend down to the ultra-trace amount scale below ppm,” she says.
The researchers are planning to measure other nanoparticles in the future as well, such as silica dioxide.