Acomplex mixture of sunscreens of different lipophilicity was quantified for the first time by thin-layer chromatography (TLC) followed by densitometric scanning in absorption mode. Multiple-development normal-phase TLC was performed on silica gel 60 as stationary phase. Two mobile phases were used: A — cyclohexane-diethyl ether 5:1 (v/v) and B — ethyl acetate-ethanol-water 70:35:30 (v/v). After development with mobile phase A, two oil-soluble sunscreens, avobenzone (AVO) and octyl salicylate (OS), were analyzed at 360 and 300 nm, respectively. Subsequent development of the same plates with mobile phase B made it possible to quantify a water-soluble sunscreen — phenylbenzimidazol sulfonic acid (PBS) at 300 nm. Calibration curves were non-linear. Limits of detection (LOD) and quantification (LOQ) were LOD (OS) 0.02 μg spot−1, LOQ (OS) 0.06 μg spot−1, LOD (AVO) 0.03 μg spot−1, LOQ (AVO) 0.08 μg spot−1, LOD (PBS) 0.02 μg spot−1, and LOQ (PBS) 0.06 μg spot−1. The method was validated and applied to the analysis of a commercially available cosmetic product.
Authors:Jarosław Pyzowski, Elżbieta Brzezińska, and Anna Weronika Sobańska
Chemical ultraviolet (UV) filters and preservatives used currently in sunscreen preparations are compounds of diverse structures, and the safety of their application depends on their inability to penetrate the skin and other barriers present in the human body. However, at least some of these chemicals meet the general requirements of the good blood—brain barrier (BBB) permeability described in the literature sources. The objective of this study was to examine the behavior of selected cosmetic raw materials (UV filters and preservatives) towards the BBB on the basis of the BBB permeability models developed in our earlier study, based on easily accessible RP-18 thin-layer chromatographic data and calculated molecular descriptors. The computed BBB permeability parameters B1 and B2 correlate with the chromatographic data (RF, RF/PSA) and calculated physicochemical descriptors usually associated with the BBB permeation (HA, Sa, DM, log D). The relationships between these values were developed by stepwise multiple regression analysis, validated, and found to explain 93–96% of the total variance. The models of the BBB permeation based on classification functions obtained previously from discriminant function analysis were used to assign the studied compounds to the groups of good (CNS+) or poor (CNS−) blood—brain barrier permeability, suggesting the inability of the majority of these compounds to cross the BBB. The universal character of BBB permeability models developed earlier was confirmed.