Credit: © 2008 ACS

More and more sunscreens now contain nanoscale particles of titanium dioxide — an active ingredient that absorbs harmful UV rays — because it provides better protection and transparency on the skin than its microscale counterparts. Various methods exist for characterizing micrometre-size particles but they are not well-suited for nanoparticles. Researchers at the University of Ferrara in Italy now report that two known analytical methods can be used to analyse the content and size of titanium dioxide nanoparticles in a commercial sunscreen.

Catia Contado and Antonella Pagnoni1 isolated the nanoparticles from the sunscreen by solvent extraction and sonication, and analysed them using flow field-flow fractionation, which separates the particles based on their mobility in a field, and inductively coupled plasma atomic-emission spectroscopy, which determines the total content based on the intensity of the emission wavelength of the ionized element. Fractions from the field-flow setup were detected using ultraviolet spectroscopy and the data was converted to a particle-size distribution using an algorithm. The eluted fractions were then measured for titanium content using atomic-emission spectroscopy and the concentration profiles were found to match the ultraviolet data. The Nivea Sun 50+ sample was shown to contain 4.75% by weight of titanium dioxide particles that were between 50–100 nm in size.

Although the method proves to be simple, rapid and cheap, techniques for analysing sunscreens in their original lotion formulation are still needed.