Supercritical fluid extraction for off-line and on-line high-performance liquid chromatographic analysis

Abstract

The on-line coupling of supercritical fluid extraction (SFE) with gas chromatography (GC) and supercritical fluid chromatography (SFC) has been described in previous chapters. In the case of GC and capillary SFC (cSFC) a commonly employed interfacing procedure involves decompressing the SFE extract on to the top of the capillary column. This results in the analyte(s) becoming band focused prior to the onset of the chromatographic stage. In packed column SFC the interfacing procedures are again relatively straightforward, generally involving either trapping the extracted analyte(s) on to the top of the analytical column (whose retentive capacity has been carefully selected) prior to supercritical decompression or decompressing the SFE extract into a trapping column which is subsequently linked to an analytical column. The on-line coupling of SFE with high-performance liquid chromatography (SFE-HPLC) is technically more challenging. This situation arises from the fundamental incompatibility of a sample preparation procedure that ultimately produces a large volume of gas with a chromatographic technique which uses a liquid mobile phase. Maintenance of a gas-free HPLC mobile phase is generally considered mandatory in order to obtain optimum pump and detector performance. Admission of gas into an HPLC system can lead to erratic pump performance and complete loss of detector stability.