Offline preparative 2-D polar-copolymerized reversed-phase chromatography × zwitterionic hydrophilic interaction chromatography for effective purification of polar compounds from Caulis Polygoni Multiflori.

Polar compounds are abundant in the water decoction of Traditional Chinese Medicines (TCMs) and possess important biological activities. However, purifying these compounds has faced great difficulties largely due to poor retention and insufficient selectivity. To solve this problem, an offline orthogonal 2-D RPLC coupled with hydrophilic interaction chromatography (HILIC) method was developed to achieve purification of polar compounds from Caulis Polygoni Multiflori. A polar-copolymerized XAqua C18 column and a zwitterionic Click XIon column exhibited satisfactory retention and separation for polar compounds. Therefore, they were adopted to construct the offline 2-D LC system. Furthermore, the method presented a high orthogonality, which was calculated to be 72%. The XAqua C18 column was used in the first dimension to fractionate the 5.1 g polar fraction with a recovery of 85% within 10 h. In the second dimension, three representative fractions were purified using the Click XIon column. Finally, three compounds with purity higher than 95% were identified for the first time from this plant. This offline 2-D RPLC/HILIC method was shown to be an effective approach to purifying polar compounds from Caulis Polygoni Multiflori.