Study Of The Interface And System Of Comprehensive Two-dimensional Liquid Chromatography

Chapter 2: In order to solve the problems in interfacing normal phase liquid chromatography (NPLC) and reversed phase liquid chromatography (RPLC), i.e. immiscibility of the mobile phases of NPLC and RPLC, and the conflict between the transferred volume from the first dimension (1^st-D) and the maximum allowable injection volume of the second dimension (2^nd-D), a vacuum-evaporation interface (VEI) was developed and was used in a two-dimensional liquid chromatographic (VEI-2D-LC) system of NPLC-RPLC. All the solvent in the loop of the interface was evaporated at 80 90°C under vacuum conditions, leaving the analytes on the inner wall of the loop. The mobile phase of the 2^nd-D dissolved the analytes in the loop and injected them onto the second column, allowing an on-line solvent exchange of a selected fraction from the 1^st-D to the 2^nd-D. The selectivity and resolution of chromatographic properties of the two dimensions was maintained at their optimal condition. Sample loss due to evaporation in the interface was observed that depended on the boiling point of the compound.Chapter 3: A comprehensive 2D-LC (C2D-LC) system with a 0.53 mm i.d. NPLC column as the 1^st-D and a monolith 4.6 mm i.d. RPLC column as the 2^nd-D was established by using a loop-valve switching interface. The interface was based on a ten-port, two-position valve with two storage loops. The fractions from 1^st-D were stored into the two storage loops alternately, and injected into the 2^nd-D sequentially. Since the volume flow of the 1^st-D is only 1/500 of that of the 2^nd-D,the incompatibility of the two dimensional mobile phases was avoided without compromise of the separation efficiency by using the system.Chapter 4: A comprehensive NPLC×RPLC system (VEI-C2D-LC) was constructed by using the VEI. A packed capillary NPLC column was used as the 1^st-D and a monolithic RPLC column was used as the 2^nd-D. A ten-port valve with two identical storage loops was used in the VEI. The solvent in the loops of the interface was evaporated at 25 oC under vacuum conditions, leaving the analytes stick on to the inner wall of the loops. The performance of the VEI-C2D-LC system was demonstrated by separation of traditional Chinese medicine extracts.Chapter 5: An axial temperature gradient (ATG) along a packed HPLC column was also exploited. A thermostat system was designed to form the effect of ATG along a microcolumn. The ATG effect on separation performance was investigated both at isocratic and gradient (MPG) in microcolumn HPLC, and was compared with the results performed at ambient conditions. Extrapolated curves of peak width at half height (w_h) vs lnk showed that wh is narrower at the same retention time when ATG was applied in addition to MPG. The column efficiency was enhanced 20³0% and the resolution was slightly reduced because of reduction of selectivity at elevated temperature at ATG condition.To achieve on-column focusing on the inlet of the second column in a two-dimensional liquid chromatographic system, a normal phase LC operated at high temperature with low organic content mobile phase was used in the 1^st-D. The separation efficiency of the 2^nd-D was maintained in the coupling of the 2-D system.