摘要：The project described in this paper illustrates the spectrophotometric UV behavior of some representative chemicals used as sun blockers and some over the counter (OTC) sunscreen lotions labeled with different sun protection factor (SPF). The experiments have been carried out in three different solvents, Cyclohexane, Methanol and Dimethyl sulfoxide, which illustrate the solvent effect in the UV spectra. Indices of UV protection have been estimated from the ratios of the areas per unit of wavelength for each UV region (UVA-I, UVA and UVB). Higher indices of UV protection are obtained for higher SPF. The broad spectrum protection (UVA protection) has also been estimated from the critical wavelength value. All OTC sunscreen lotions studied comply with broad spectrum labeling, λ(crit.) ≥370 nm, while the sun blockers studied cannot be classified as such. When comparing the UV spectra for sunscreen lotions that have aged for one year with freshly produced sunscreen, a shift toward the UVB region for aged lotion can be observed. UVA/UVB ratio is the parameter of choice to describe the aging effect, while λ(crit.) is practically insensitive to aging. Sunscreen aging is accompanied by UVA protection failure and therefore renewing sunscreens each season is to be recommended. This project has been carried out for final year students in Chemistry and Pharmacy at different degrees of difficulty.
