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- 1. Supercritical Fluid Extraction in Food Analysis
- 2. 2 Basic Definitions Critical temperature (Tc) The maximum temperature at the critical point at which a gas can be converted in to a liquid by an increase in pressure Critical pressure (Pc) The minimum pressure that would suffice to liquefy a substance at its critical temperature Critical point The characteristic temperature (Tc) and pressure (Pc) above which a gas cannot be liquefied Supercritical fluid The defined state of a compound, mixture, or element above its critical pressure (Pc) and critical temperature (Tc). It is gas like compressible fluid that takes a shape of its container and fills it. It is not a liquid but has liquid like densities (0.1-1 g/mL) and solvating power
- 3. 3 Basic Definitions… Reduced temperature (Tr) The ratio of the temperature (T) in the system to the critical temperature (Tc) (Tr) = T/Tc Reduced pressure (Pr) Ratio of the pressure in the system (P) to the critical pressure (Pr) = P/Pc Supercritical fluid extraction (SCF) Extraction of a material using a supercritical fluid Coupled Supercritical fluid extraction- Supercritical fluid chromatography In this system sample is extracted with a Supercritical fluid, which then places the extracted material in the inlet port of a Supercritical fluid chromatographic system. The extract is chromatographed directly using a Supercritical fluid
- 4. 4 Important Properties of Supercritical fluids Remarkable ability to dissolve large, non-volatile molecules e.g., supercritical CO2 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 CO2 can be recovered by reducing the pressure and allowing the CO2 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
- 5. 5 Instrumentation: Instrumentation for SF-Chromatography is very similar to ordinary HPLC equipment since the temperature & pressure requirements for supercritical fluids fall within the standard operation Two Major Differences • Thermostated column oven • requires precise temperature control of mobile phase (typically supercritical CO2) • Restrictor or back-pressure device • required to maintain desired pressure in column • pressure change to convert from supercritical fluid to a gas for transfer to detector
- 6. 6 Supercritical Fluid Extraction Mechanism Four main mechanisms of Supercritical Fluid Extraction 1. If there in no interaction between solute and the solid phase, the process is simple dissolution of the solute in a suitable solvent that does not dissolve in the solid matrix 2. If there are interaction between solid and the solute, then the extraction process is termed as desorption and the adsorption isotherm of the solute on the solid in presence of the solvent determines the equilibrium. Most solid extraction processes, e.g activated carbon regeneration, falls in this category
- 7. 7 Supercritical Fluid Extraction Mechanism… Four main mechanisms of Supercritical Fluid Extraction… 3. Third mechanism is swelling of solid phase by the solvent accompanied by extraction of the entrapped solute through the first two mechanisms, e.g. extraction of pigments or residual solvents from polymeric matrices 4. Fourth mechanism is reactive extraction where the insoluble solute reacts with the solvent and the reaction products are soluble hence extractable, e.g. extraction of lignin from cellulose. Extraction is always followed by another separation process where the extracted solute is separated from the solvent
- 8. 8 Flow Diagram of an SFE System CO2 cylinder Condenser Pump Heater Extraction vessel Separation Raw material Product Product
- 9. 9 SCF Batch Extraction SCF cosolvent cosolvent Pumps Gas
- 10. 10 SCF continuous Extraction CO2 + Solute Pressure reduction Extracted material High pressure CO2 CO2 CO2 Low pressure Solvent recycling Pumps
- 11. 11 Advantages of SFEs 1) Supercritical fluids have a higher diffusion coefficient and lower viscosity than liquids 2) Absence of surface tension allows for their rapid penetration into the pores of heterogeneous matrices, which helps enhance extraction efficiencies 3) Selectivity during extraction may be manipulated by varying the conditions of temperature and pressure affecting the solubility of the various components in the supercritical fluids 4) Supercritical fluids extraction does not leave a chemical residue 5) Supercritical fluids extraction can use carbon dioxide gas, which can be recycled and used again as a part of the unit operation
- 12. 12 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 Contain no functional group that makes possible detection in LC using Separations are faster then LC Run at lower temperature than GC Beneficial in industrial scale purification
- 13. 13 SFE Applications in Food Products Sr. No. Food items Application 01 Meats and pickles Paprika color (oleoresin) extraction 02 Coffee and Tea Caffein (decaffeination process) 03 Vegetables Oils and fats extraction 04 Herbs Extraction of herbal medicines 05 Botanicals Food colors extraction 06 Plant materials Antioxidants extraction 07 Tobacco Denicotinization 08 Fruit juices Stabilization of fruit juices 09 hops Bitter extraction 10 Fast food De-oiling 11 Meat and pharmaceutical items Thyme oil extraction