Chromatographic recovery and purification of natural phytochemicals from underappreciated willow bark water extracts

Willow (Salicaceae) bark contains a variety of antioxidant phytochemicals depending mainly on the hybrid. In this study, hot water extraction of willow bark was coupled with a sequential preparative scale chromatography to purify the crude extracts to a well-separated and highly concentrated phytochemical fraction. The pre-equilibrated hydrophilic weak cation exchange resins (with acrylic matrix in Na⁺ ions form) achieved a good separation of phytochemicals from monosaccharide fractions. Secondly, the individual phytochemical can be purified based on their size and hydrophobicity differences, using gel permeation chromatography and adsorption column chromatography. Surprisingly, the G-types of sephadex demonstrated an efficient separation of not only monosaccharides but a complete separation between (+)-catechin and triandrin. Picein and salicin can be further separated according to their hydrophobicity differences. The purified compounds can be quickly quantified using high performance liquid chromatography, gas chromatography and high-performance anion-exchange chromatography. The purified picein and triandrin were characterized by one- and two-dimensional nuclear magnetic resonance spectroscopy techniques. Additionally, the authentic compounds were applied to confirm the identification, quantification and purity. The technique described here might be a fast, economical, and highly efficient way in the large-scale isolation and purification of the phytochemical compounds from willow bark.