Identification of crystalline solids in sunscreen using x-ray powder diffraction
Abstract:We cannot imagine spending our time on a seaside and outside during sunny summer months without any sunscreen. Sunscreens protect us from harmful UV rays. But which sunscreen ingredients protect us from those so-called harmful UV rays? This was the main purpose of my thesis, to determine crystalline phases and the active ones among them in sunscreens using X-ray powder diffraction.
The principle of X-ray powder diffraction is the usage of X-ray waves with a specific wavelength to irradiate a sample. This results in various reflections from a crystalline solid, recorded by the detector. X-ray powder diffraction results in a diffraction pattern to help identify a substance. I opened and read the diffraction patterns using the X'Pert HighScore Plus program, in which I compared individual samples with each other and, based on common peaks, compared those peaks with the standards in another program Crystallographica Search-Match, containing a database. In cases of unexplained peaks, I looked at individual ingredients list of samples and, based on common ingredients, identified possible organic crystalline ingredients using the ConQuest and Mercury programs.
When going through the literature I found out that there are two types of UV filters: organic and inorganic. The main representatives of inorganic filters are titanium dioxide and zinc oxide. Identification of those two UV filters did not cause any problems unlike the organic ones. Through the comparisons of declarations and usage of the ConQuest and Mercury programs, I was able to identify the organic filter of methylene bis-benzotriazolyl tetramethylbutylphenol, known by the other name bizoktrizol. In addition to the UV filters mentioned, I also identified the remaining inactive crystalline substances that are added to the sunscreens to improve stability, skin absorption and appearance.