CONSTRUCTION OF A ROBUST STAINLESS-STEEL CLAD FUSED-SILICA RESTRICTOR FOR USE IN SUPERCRITICAL-FLUID EXTRACTION

Fused-silica restrictors used for off-line supercritical fluid extraction (SFE) frequently break when extractions are performed with polar supercritical fluids [e.g., CHClF2 (Freon 22) or CO2 containing polar modifiers (e.g., methanol)]. Securing the fused-silica restrictor inside a 1/16 in. (1.6 mm) O.D. stainless-steel tube with an epoxy resin eliminated the restrictor breakage and allowed restrictors to be connected to the extraction cell with conventional stainless-steel fittings. The stainless-steel clad fused-silica restrictor was simple and inexpensive to construct, physically robust, and proved ideal for SFE applications since no artifacts from the clad restrictor were detected in the collection solvent.