421-821-chapter-29-30

421-821-chapter-29-30 - Supercritical Fluid Chromatography...

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Supercritical Fluid Chromatography Introduction : Supercritical Fluid Chromatography (SFC) is a hybrid of gas and liquid chromatography that combines some of the best features of both Supercritical Fluid exist at temperatures and pressures above its critical temperature and pressure and have densities, viscosities and other properties that are intermediates between those of the substance in its gaseous and liquid state. Gas (STP) Supercritical Fluid Liquid Density (g/cm 3 ) (0.6-2) x 10 -3 0.2-0.5 0.6-2 Diffusion coefficient (cm 2 /s) (1-4)x10 -1 10 -3 -10 -4 (0.2-2)x10 -5 Viscosity (g cm -1 s -1 ) (1-3)x10 -4 (1-3)x10 -4 (0.2-3)x10 -2 Critical temperature temperature above which a distinct liquid phase does not exist regardless of pressure
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Important Properties of Supercritical fluids – remarkable ability to dissolve large, non-volatile molecules e.g., supercritical CO 2 can dissolve n-alkanes containing over 30 carbon atoms related to their high densities dissolved analytes are easily recovered equilibrate with atmosphere at relatively low temperatures e.g., analyte in supercritical CO 2 can be recovered by reducing the pressure and allowing the CO 2 to evaporate no need for organic solvents environmentally friendly – inexpensive, innocuous and non-toxic – higher diffusion coefficients and lower viscosities relative to liquids faster and higher resolution separations
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Advantages of SFC compared to LC and GC: - SFC can separate compounds that are not conveniently handled by GC or LC. non-volatile or thermally labile and contain no functional group that makes possible detection in LC using spectroscopic or electrochemical techniques up to 25% of all separation problems fall into this category u u examples include: polymers, fossil fuels, pesticides, foods, drugs, etc - Separations are faster then LC - Run at lower temperature than GC - Beneficial in industrial scale purification Faster elution Reduction in peak width (a3) Reduction in elution time (4x)
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Instrumentation :
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421-821-chapter-29-30 - Supercritical Fluid Chromatography...

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