PREPARATION OF LONG PACKED CAPILLARY COLUMNS USING CARBON-DIOXIDE SLURRIES

A new, reproducible method is described for the preparation of highly efficient fused silica packed capillary columns using pressure program med liquid or supercritical carbon dioxide to carry the packing materi al into the capillary. The method allows facile preparation of long, u niformly packed capillary columns capable of producing over 240,000 th eoretical plates in SFC. Columns of up to 10 meters in length were pre pared using LC packing materials of different chemical nature and part icle size. The new method does not require a separate step for prepari ng the slurry and it is free from the drawbacks inherent in convention al slurry-packing methods. The lower viscosity and surface tension of carbon dioxide compared to conventional slurry-forming liquids, as wel l as the use of ultrasonic vibration and pressure programming in the p acking process, provide favorable conditions for achieving packing uni formity over greater column lengths than is achievable by other packin g techniques. Proper restrictors and appropriate decompression rates d uring the use of these columns in SFC were found to be very important in achieving optimum column performance. In comparison to the use of o pen tubular columns, higher efficiencies, greater sample capacities, a nd faster analysis speeds can be obtained. These advantageous features make the newly developed columns suitable for trace analysis, separat ion of very complex mixtures, and analysis of difficult-to-separate so lutes.