A modified approach for the determination of sulfate in cosmetics and personal care products by UV–Vis spectroscopy using response surface methodology

In recent years, “sulfate-free” products have become increasingly common for most cosmetics and personal care products. With a boom in the number of sulfate-free claims, an analytical method for determining sulfate is certainly needed. Analysis of sulfate in cosmetic products can be difficult due to matrix interference and the complex nature of the ingredients used in the formulation. A simple and novel modified method for the determination of sulfate was developed by using UV–Vis spectroscopy. The procedure involved the precipitation of sulfate as barium sulfate and the removal of interference under controlled conditions, using different reagents such as acid, glycerol and ethanol. The method was optimized for the best conditions using response surface methodology. According to the experimental design, nitric acid and glycerol at 2% concentration yielded the maximum absorbance and the optimized method was validated in terms of linearity, accuracy, precision, limit of detection and limit of quantification. Fifteen market samples belonging to the shampoo and conditioner product types were analyzed to evaluate the performance of the optimized method. The results obtained were found to be satisfactory, and the proposed method is linear (R²—0.9971), accurate (89 to 92%), precise (%RSD < 4) and robust (% deviation < 5) with limit of detection (4.2 mg/l), limit of quantification (12.59 mg/l) and can be employed for the analysis of sulfate in cosmetics and personal care products.