Abstract: A comprehensive two-dimensional liquid chromatography(NPLC×RPLC) was developed. Normal phase liquid chromatography(NPLC) with a CN microcolumn was used as the first dimension, and reversed-phase liquid chromatography(RPLC) with a monolithic column was used as the second dimension. The interface was based on a ten-port, two-position valve with two storage loops. The first column was operated at a flow rate of 8 μL/min in isocratic mode, while the monolithic column flow rate was 4 mL/min and was operated in gradient mode. The sample loops had a volume of 12 μL each, and the analysis time in the second dimension was 1.5 min. The primary fractions were stored into the two storage loops alternately, and then were separated by the secondary column sequentially. AUV detector was used after the secondary column. The use of a monolithic column in the second dimension permits a very fast analysis operating at highter flow rates without loss of resolution, since the monolithic column has higher permeability than conventional packed columns. The incompatibility of the two dimensional mobile phases was avoided because the flow rate of the first dimension is only 1/500 of that of the second dimension. The performance of the system was evaluated by several standards mixture and Radix salviae miltiorrhiza bage extract and the advantage of using 2D-LC over one-dimensional chromatographic techniques is clearly demonstrated in the analysis of the extract.

Key words: Comprehensive two-dimensional LC, NPLC×RPLC coupling technique, Sample loops-valve interface, Traditional Chinese medicine, Radix salviae miltiorrhiza bage