In vitro evaluation of sun protection factor of sunscreens using infrared spectrometry and chemometrics

Solar radiation consists of several different fractions i.e. infrared, visible and ultra-violet radiation. The research and studies in the past few decades have shown that sunlight ultra-violet rays cause a lot of diseases and skin damages such as erythema, pigmentation and cancer.[1] Sunscreens protect skin by absorbing and/or reflecting UV/IR rays via chemical and physical filters. It is required that all sunscreens contain a sun protection factor (SPF) label.[2] It was aimed to evaluate the SPF of sunscreen cosmetic products by a non-destructive and reliable analytical approach.[3] Thus, in this research, FTIR spectroscopy was employed to analyze the SPF of sunscreen cosmetic product samples and determination of physical and chemical sunscreen. Totally 71 sunscreen samples were used in which 21 samples were of SPF 30, 18 samples were of SPF 50, 22 samples were of SPF 60 and 9 samples were of SPF 90. On the other hand, 19 samples contained physical protectors while remaining 52 samples contained chemical ones. Mid-IR spectra of the provided samples were recorded by attenuated total reflectance (ATR) sampling technique.[4] Principle component analysis (PCA) and support vector machine (SVM) as representative of unsupervised and supervised learning methods- were utilized for data classification. Obtained data revealed SVM as a reliable approach, due to its efficiency in pattern recognition of the sunscreen samples via their FTIR spectras. Prediction error for the test set in binary and quaternary class classifications were 9.5 % and 5.0% respectively.