Analysis of the Active Ingredients in Sunscreen: A Multiweek Experiment for the Analytical Chemistry Laboratory

We describe a multiweek laboratory module that has been successfully implemented with upper-division undergraduate students in an undergraduate analytical chemistry course for six years. The laboratory module includes analysis of organic (octocrylene and avobenzone) and inorganic (ZnO and TiO2 nanoparticles) UV filters in sunscreens. Over the course of 3 weeks, students perform qualitative and quantitative analyses of sunscreens using UV-vis spectroscopy, X-ray diffraction (XRD), and high-performance liquid chromatography (HPLC). Using UV-vis, students qualitatively evaluate the range of UV radiation over which the UV filters and sunscreens are effective. Students also quantitatively determine the concentration of ZnO nanoparticles in a mineral sunscreen as 20 +/- 8 (% w/w, n = 19) compared to 21.6% reported by the manufacturer. Using XRD, students explore the properties of ZnO and TiO2 nanoparticles by comparing their diffraction properties to bulk ZnO and TiO2 using the Debye-Scherrer formula. Students also explore the different crystal phases of TiO2 (rutile and anatase) and use the distinct diffraction patterns of each standard to confirm the presence of ZnO and TiO2 nanoparticles in mineral sunscreens. In addition, students analyze the organic sunscreen to highlight that the noncrystalline organic UV filters are not suitable for XRD analysis. Using HPLC, students quantitatively determine the concentrations of octocrylene and avobenzone in an organic sunscreen. Students' results demonstrate a high degree of precision and accuracy with measured values of 9.5 +/- 0.5 (% w/w) octocrylene and 2.7 +/- 0.2 (% w/w) avobenzone (n = 18) compared to respective values of 10% and 3% reported by the manufacturer. Finally, we describe the assessment of student performance through writing assignments, which has been shown to be an effective way to help students synthesize their data and make connections and comparisons among instrumental analysis techniques.