Single-Step Process for Isolation of Pure Quercetin\nfrom Aqueous Extract of Waste Onion Peels

Onion\npeel is a rich source of quercetin. Toward developing green\nmethods to obtain pure quercetin, water-based extraction of quercetin\nfollowed by a simple single-step liquid–liquid extraction (LLE)\nmethod for the efficient isolation of quercetin is reported in this\nstudy. The developed method (LLE) obviates the need for commonly reported\ncolumn chromatography. The purity of solid quercetin recovered was\nestablished using thin-layer chromatography (TLC), ultraviolet–visible\nspectroscopy (UV–vis), Fourier transform infrared spectroscopy\n(FTIR), high-performance liquid chromatography (HPLC), gas chromatography\n(GC), high-resolution mass spectroscopy (HRMS), and nuclear magnetic\nresonance (NMR). The purity of quercetin obtained from LLE was better\nat 93 ± 2% than the purity obtained from column chromatography\n(86 ± 2%). Optimization of the developed LLE process resulted\nin ∼600-fold reduction of the solvent used per milligram of\nquercetin purified. The maximum yield of quercetin was 10.88 ±\n0.2 mg/g dry scales of onion, obtained by LLE, compared with 2.12\n± 0.3 mg/g dry scales of onion obtained from column chromatography.\nThe LLE method thus becomes more sustainable and easy to scale up\nwith improved process efficiency and enhanced product quality.