Spectrophotometric determination of quercetin using micelles of cetyltrimethylammonium bromide in a low ratio methanol–water mixture

A simple and achievable UV-Vis spectrophotometric method for the micro-quantitative determination of quercetin has been developed and validated. This method relies on the formation of supramolecular assemblies of quercetin (QR) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in a 5 % methanolic aqueous solution. In this solvent medium, CTAB in the presence of QR has a critical micelle concentration of 1.2·10-3 mol l-1 at 24 °C, determined through conductometry. Important analytical parameters such as wavelength, composition of methanol-water mixture, CTAB concentration (cCTAB), and pH were optimized. Under the optimum experimental conditions (l = 397 nm, 5 % methanol as solvent, cCTAB = 2.0·10-3 mol l-1, and pH = 6.0), Beer's law was valid for QR concentrations up to 16.9 mg ml-1. The Ringbom optimum QR concentration range was 1.0 - 16.9 mg ml-1. The method sensitivity was 2.03·104 l mol-1 cm-1 (the molar absorptivity) and 0.13 mg ml-1 (limit of detection). The applicability of the proposed method for quantifying QR in pharmaceutical formulations was demonstrated. Furthermore, the proposed UV-Vis spectrophotometric method was successfully applied to the reliably assay of QR, even in the presence of vitamin C.