Supercritical fluids can be used to extract analytes from samples. The main advantages of using supercritical fluids for extractions is that they are inexpensive, contaminant free, and less costly to dispose safely than organic solvents. For these reasons supercritical fluid CO2 is the reagent used to extract caffeine from coffee.
The properties of supercritical fluids also provide some advantages for analytical extractions. Supercritical fluids can have solvating powers similar to organic solvents, but with higher diffusivities, lower viscosity, and lower surface tension. The solvating power can be adjusted by changing the pressure or temperature, or adding modifiers to the supercritical fluid. A common modifier is methanol (typically 1-10%) which increases the polarity of supercritical CO2.
Pictures of supercritical fluid extractors
/chem-ed/sep/sf/sfe.htm, updated 11/1/96
Copyright © 1996 by Brian M. Tissue, all rights reserved.
Science Hypermedia Home Page