Calculation of Sun Protection Factor (SPF) Values for Selected Organic Filters Using a UV Spectrophotometer

This study analytically investigated the ultraviolet (UV) absorption characteristics of various organic UV filters containing a benzoyl or benzylidene group, using a double-beam UV–Vis spectrophotometer to measure their absorbance. Additionally, the sun protection factor (SPF) of these compounds was calculated using Mansur’s equation—a critical metric for assessing their effectiveness against harmful UV radiation. Absorbance measurements were conducted over the wavelength range of 290 to 320 nm in methanol, focusing on organic acid salts such as sodium benzoate, sodium salicylate, and ammonium benzoate, as well as organic acids and aldehydes. The results demonstrated that the organic filters provided varying levels of UV protection. The highest SPF value recorded was 54.5 for 4-methoxybenzaldehyde, followed by benzophenone at 44.6, trans-cinnamaldehyde at 41.4, and cinnamic acid at 39.3. These data suggest that benzoyl derivatives with conjugated double bonds exhibit significantly greater UV absorption than benzoic acid and salicylic acid, which displayed relatively modest SPF values. In light of these findings, it is recommended that benzophenone, trans-cinnamaldehyde, and cinnamic acid be considered for incorporation into sunscreen formulations due to their demonstrated efficacy in UV protection.