The use of modifiers in supercritical fluid chromatography and extraction has become quite common due to the inability of pure carbon dioxide alone to solvate many of the compounds of interest. The effects of modifiers in supercritical fluid chromatography have been more thoroughly studied than the effects of modifier in supercritical fluid extraction. The effects of modifier on trapping efficiencies for off-line supercritical fluid extraction have been evaluated in this work. Sorbent and solid phase traps were investigated with pure carbon dioxide in order to determine the effect of stationary phase identity, pretreatment, and rinse solvent on the recoveries of a test mixture of compounds of varying vapor pressure and molecular weight. The solid phase traps, which were polyethylene frits, performed as well as the sorbent traps in most cases, and significantly better than the sorbent traps in many cases. The ability to cool these traps to -20°C allowed for efficient trapping of volatile compounds without the benefit of sorptive interactions. Sorbent and solid phase traps were then studied with the addition of 1%, 2%, 4%, and 8% methanol to the mobile phase. The sorbent trap explored consisted of 40 µm ODS packing material, while the solid phase trap consisted of 100 yum stainless steel beads. In this work trap temperatures ranged from 5-80°C. It was found that trap temperature, modifier concentration, and trap type influenced recoveries of the test mixture components. Applications of these solid phase and sorbent traps explored were the extraction of polychlorinated biphenyls from river sediment and the extraction of the active components from a drug formulation. The separation of some compounds of pharmaceutical interest was also explored, where the addition of modifier, and in some cases an additive, was required to elute compounds from the chromatographic column. / Ph. D.