Two-dimensional liquid chromatography for the separation of Liuwei Dihuang Pills

A simple on-line two-dimensional liquid chromatographic system was constructed using strong cation exchange chromatography (SCX) followed by reversed phase chromatography (RP) to analyse Chinese patent medicine Liuwei Dihuang Pills. A 2-position-6-port valve was used as a switch interface to connect two common size (250 mm x 4. 6 mm i. d.) columns. The experiment was carried out as follows: the sample, after the first dimensional cation exchange (Hypersil SCX), was enriched on the head of RP analytical column C,) through the 6-port valve; By switching the valve, the fractions from the SCX were transferred to RP for further separate. Eluted by discontinuous 11 steps with increasing salt concentration, the system led to over 550 peaks, with the total peak capacity high up to 2266. Compared with one-dimensional chromatography, the system got large improvement in the resolution and total peak capacity. The sample which could not be separated in the one-dimensional model, but be separated well in the two-dimensional system.