Development and Validation of a Stability Indicating RP-HPLC Method for the Determination of Two Sun Protection Factors (Koptrizon and Tinosorb S) in Topical Pharmaceutical Formulations Using Experimental Designs

A novel, simple, validated stability indicating HPLC method was developed for determination of Koptrizon and Tinosorb S. Stability indicating power of the method was established by forced degradation study. The chromatographic separation was achieved with Waters X Bridge column, by using mobile phase consisting of a mixture of acetonitrile？:？tetrahydrofuran？:？water (38？:？38？:？24, v/v/v). The method fulfilled validation criteria and was shown to be sensitive, with limits of detection (LOD) and quantitation (LOQ) of 0.024 and 0.08？μg？ for Koptrizon and 0.048 and 0.16？μg？ for Tinosorb S, respectively. The developed method is validated for parameters like precision, accuracy, linearity, solution stability, specificity, and ruggedness as per ICH norms. Design expert with ANOVA software with linear model was applied and a 23 full factorial design was employed to estimate the model coefficients and also to check the robustness of the method. Results of the two-level full factorial design, 23 with 10 runs including two-centre-point analysis based on the variance analysis (ANOVA), demonstrated that all three factors, as well as the interactions between retention time of Koptrizon, Tinosorb S, and USP plate count for Koptrizon, are statistically significant. 1. Introduction Frequent exposure to UV radiation causes pronounced harmful effects on human health. UV radiation-induced effects are manifested as acute responses, namely, sunburn, hyperplasia, and immunosuppressant, and as chronic responses, primarily photo carcinogenesis and photo ageing [1]. The molecules employed in cosmetic products to protect skin from the sun are classified as physical and chemical sunscreens. Physical sunscreens are represented mainly by zinc and titanium oxides which interrupt the path of UV light by scattering or reflection. Chemical sunscreens are generally aromatic compounds conjugated with an electron-donating group in “ortho” or “para” position and an electron acceptor group. This chemical structure favours electron delocalization and therefore helps excitation of molecules from ground state to an excited state. The energy required for this transition corresponds to the energies of ultraviolet A (UVA) and Ultraviolet B (UVB) radiations [2, 3]. Chronic exposure to UVB (280–320？nm) wavelengths induces damage to human skin, such as burns and erythema, but increases evidence of demonstrates that UVA radiation (320–400？nm) contributes to photo aging, which results in the accumulation of massive amounts of abnormal elastic material in the dermis of photo-aged skin and modification in