pH‐zone‐refining elution–extrusion countercurrent chromatography: Separation of hydroxyanthraquinones from Cassiae semen

Abstract

Seven hydroxyanthraquinones were successfully separated from the traditional Chinese medicinal herb Cassiae semen by conventional and pH-zone-refining countercurrent chromatography with an environmentally friendly biphasic solvent system, in which elution-extrusion mode was investigated for pH-zone-refining countercurrent chromatography for the first time. A two-phase solvent system composed of n-hexane/ethyl acetate/ethanol/water (5:3:4:4, v/v/v/v) was used for the conventional countercurrent chromatography while the same system with a different volume ratio n-hexane/ethyl acetate/ethanol/water (3:5:2:6, v/v/v/v) was used for pH-zone-refining countercurrent chromatography, in which 20 mmol/L of trifluoroacetic acid was added in the organic phase as a retainer and 15 mmol/L of ammonia was added to the aqueous phase as an eluter. A 400 mg crude sample could be well separated by pH-zone-refining countercurrent chromatography, yielding 53 mg of aurantio-obtusin, 40 mg of chryso-obtusin, 18 mg of obtusin, 24 mg of obtusifolin, 10 mg of emodin, and 105 mg of the mixture of chrysophanol and physcion with a purity of over 95.8, 95.7, 96.9, 93.5, 97.4, 77.1, and 19.8%, as determined by high-performance liquid chromatography. Furthermore, the difference in elution sequence between conventional and pH-zone-refining mode was observed and discussed.

Full use of the liquid nature of the stationary phase: The development of elution‐extrusion counter current chromatography

“…Bu et al [20] studied the elution‐extrusion mode in the pH‐zone‐refining CCC. The seven hydroxyanthraquinones were separated from the traditional Chinese medicinal herb Cassiae semen , and the complete separation of the five components was successfully achieved separation.…”

“…(B) The upper phase was used as the mobile phase after 210 min for elution‐extrusion mode (Reproduced and adapted from Ref. [20])…”

Preparative separation of bioactive polyphenol resveratrol from Polygonum cuspidatum Sieb. et Zucc. by pH‐zone‐refining countercurrent chromatography

“…Generally more than ten fold sample loading capacity can be achieved for pH-zone-refining countercurrent chromatography compared with conventional countercurrent chromatography, which constitutes the main advantage for preparative separation by pH-zone-refining mode. At present, many papers are available for separation of acidic and basic components from complicated matrix of natural products [23][24][25][26][27][28][29][30][31] or synthetic mixtures [32][33][34][35], in which all the analytes to be separated are typical organic acids or bases in light of their carboxyl group or amino group. It is assumed that pH-zone-refining mode can only be applied in separation of ionic components and it has been well explored in preparative separation of typical organic acids or bases.…”

Application of pH‐zone‐refining countercurrent chromatography in the chiral separation of two β‐adrenergic blocking agents

“…In recent years, Abbreviation: TEBA, triethylbenzylammonium chloride Conflict of interest: The authors declared no conflict of interest. pH-zone-refining countercurrent chromatography has been effectively and successfully applied in the separation of acidic and basic components from complicated matrix of natural products [9][10][11][12][13][14][15] or synthetic mixtures [16][17][18].…”

“…Ionic components form a highly concentrated rectangular peak associated with its specific pH value by adding a retainer in the stationary phase and a eluter in the mobile phase and thus they could be purified easily from nonionic impurities . In recent years, pH‐zone‐refining countercurrent chromatography has been effectively and successfully applied in the separation of acidic and basic components from complicated matrix of natural products or synthetic mixtures .…”