SAMPLE INTRODUCTION IN CAPILLARY SUPERCRITICAL FLUID CHROMATOGRAPHY USING SEQUENTIAL DENSITY GRADIENT FOCUSING AND SOLVENT VENTING

A technique was developed for large volume sample introduction in capillary supercritical fluid chromatography. A 20-cm length of 200-mu-m i.d. capillary tubing was used as precolumn. The precolumn temperature could be easily controlled by passing an electrical current through an electrically conductive paint coated on its outer surface. During injection, the sample solvent was vented from the precolumn with CO2 (gas) at 32 atm, while the precolumn was kept at room temperature. Solutes were transferred onto the head of the analytical column as a narrow band by density gradient focussing, which was established with (a) a temperature gradient along the precolumn, (b) a rapid expansion of CO2 from supercritical fluid to gas, and (c) a temperature difference between the precolumn and the analytical column. This injection approach minimized solute mass discrimination and could be easily performed.