[Establishment of a coupling method of high performance liquid chromatography and capillary gas chromatography]

An on-line coupling system of normal phase microbore HPLC and capillary GC has been established, in which retention gap technique with on-column injection and partially concurrent solvent evaporation with early vapor exit were used. The conditions suitable for the coupling system of HPLC and CGC must be determined experimentally since the factors have to be adjusted with respect to solvent evaporation temperature and column inlet pressure etc. The suitable solvent evaporation temprature for the mobile phase used for this system, n-hexane, was about 70 degrees C. A temperature much, lower or higher than 70 degrees C will influence the GC analysis. In addition, solvent evaporation temperature and column inlet pressure are interacting, that is, higher solvent evaporation temperature needs higher inlet pressure. At the above evaporation temperature, the suitable inlet pressure for this system was about 0.2MPa. In order to minimize the extra-column effect on the LC peaks, thin transfer-line and connectors of zero-dead volume between LC column and GC column must be used. The separation and analysis of aromatics in a light diesel fuel was performed by using this system with 15cm x 2mm i.d. YGW (5microm) silica LC column and 60m x 0.25mm i.d. OV-101 GC column under the above conditions. The analytical results show that the system of on-line coupling of HPLC with CGC is a reliable analytical tool for microcomponents in complex mixtures, especially for those requiring sample preparation prior to GC.