Adsorption Equilibria of Rutin and Kaempferol-3‑O‑Rutinoside on CN-Bonded Silica from Supercritical Carbon Dioxide/Methanol

Rutin and K3R (kaempferol-3-O-rutinoside) in tartary buckwheat are flavonol glycosides with high medical value. It is necessary to separate them from tartary buckwheat before utilization because of their different medical functions. However, they have very similar molecular structures, causing troubles in thorough separation. The adsorption equilibrium of rutin and K3R from supercritical CO₂/methanol was investigated. The adsorption capacities were measured by the elution at characteristic point method at 308.15, 313.15, and 318.15 K with 0.450–0.693 g/cm³ CO₂/methanol on CN-bonded silica. The adsorption capacity of rutin and K3R showed a decreasing trend with the increasing mobile phase density and temperature. The capacity of rutin is larger than that of K3R under the same conditions, indicating that rutin was an easily adsorbed component. The data obtained from adsorption equilibria were fitted by both Freundlich and Langmuir isotherm models, which showed that the latter one performed better. This single-component model can extend to binary component and describe the competitive behavior well. Data and models obtained can be used to simulate adsorptive separation processes so as to design and optimize the separation process of rutin and K3R with supercritical fluid chromatography.