LARGE-VOLUME INJECTION IN PACKED-CAPILLARY SUPERCRITICAL-FLUID CHROMATOGRAPHY

Injection of large sample volumes in packed-capillary supercritical fluid chromatography (SFC) with the thermionic detection (TID) was performed using a packed precolumn set-up. The precolumn (2.0 x 1.0 mm I.D.) was loaded with an aqueous sample and dried with nitrogen at room temperature. After drying, desorption with a supercritical fluid to the analytical column was performed by switching restrictors mounted on valves. During desorption the analytes were focused on the top of the analytical column and next the analysis was started by again switching the restrictors. Parameters influencing the system, e.g., desorption strength of the supercritical fluid, desorption volume and desorption flow-rate, were studied. By injecting large, i.e., 75 mu l, volumes of an aqueous sample, the analyte detectability was improved ca. 1000-fold compared with conventional 100-nl injections in hexane. This resulted in limits of detection of about 1 mu g l(-1) for three oxganophosphorus pesticides. The repeatability at the 5-15 mu g l(-1) level was better than 7% (n = 8), and good linearity over two orders of magnitude was found with spiked river water samples. To emphasize the potential of the system, a larger precolumn (10 x 2.0 mm I.D.) was tested, which was loaded with 47 ml of a river water sample. A further 1000-fold gain in sensitivity was obtained, and detection limits for the one-line trace enrichment-SFC-TID set up now were in the 0.1 ng l(-1) range.