1 / 16

Supercritical Fluid Chromatography

Supercritical Fluid Chromatography. Theory Instrumentation Properties of supercritical fluid Critical temperature Above temperature liquid cannot exist Vapor pressure at critical temperature is critical pressure T and P above critical T and P Critical point Supercritical fluid.

baird
Download Presentation

Supercritical Fluid Chromatography

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Supercritical Fluid Chromatography • Theory • Instrumentation • Properties of supercritical fluid • Critical temperature • Above temperature liquid cannot exist • Vapor pressure at critical temperature is critical pressure • T and P above critical T and P • Critical point • Supercritical fluid

  2. Supercritical fluid • Above the critical temperature • no phase transition regardless of the applied pressure • supercritical fluid is has physical and thermal properties that are between those of the pure liquid and gas • fluid density is a strong function of the temperature and pressure • diffusivity much higher a liquid • readily penetrates porous and fibrous solids • Low viscosity • Recovery of analytes • Return T and P

  3. Typical Supercritical Solvents

  4. Supercritical fluid chromatography • Combination of gas and liquid • Permits separation of compounds that are not applicable to other methods • Nonvolatile • Lack functional groups for detection in liquid chromatography

  5. Supercritical Fluid Extraction • near the critical point properties change rapidly with only slight variations of pressure. • inexpensive, • extract the analytes faster • environmentally friendly • sample is placed in thimble • supercritical fluid is pumped through the thimble • extraction of the soluble compounds is allowed to take place as the supercritical fluid passes into a collection trap through a restricting nozzle • fluid is vented in the collection trap • solvent to escapes or is recompressed • material left behind in the collection trap is the product of the extraction • batch process

  6. Capillary Electrophoresis • Separations based on different rate of ion migration • Capillary electrochromatography separates both ions and neutral species • Electroosmotic flow of buffer acts as pump • Principles • Applications

  7. Planar electrophoresis • porous layer • 2-10 cm long • paper • cellulose acetate • polymer gel • soaked in electrolyte buffer • slow • difficult to automate

  8. Capillary Electrophoresis • narrow (25-75 mm diameter) silica capillary tube • 40-100 cm long • filled with electrolyte buffer • fast • complex but easy to automate • quantitative • small quantities • nL

  9. Separation • Movement of ions function of different parameters • molecular weight • charge • small/highly-charged species migrate rapidly • pH • Deprotonation HAH+ + A- • ionic strength • low m • few counter-ions • low charge shielding • high m, • many counter-ions • high charge shielding

  10. Migration rate • v= migration velocity • me=electrophoretic mobility (cm2/Vs) • E=field strength (V/cm) • For capillary • V=voltage • L=length • Electrophoretic mobility depends on net charge and frictional forces • Size/molecular weight of analyte • Only ions separated • Plate height (H) and count (N) • Function of diffusion and V

  11. Plates • Planar electrophoresis • large cross-sectional area • short length • low electrical resistance, high currents • Sample heating Vmax=500 V • N=100-1000 low resolution • Capillary electrophoresis • small cross-sectional area • long length • high resistance • low currents • Vmax=20-100 kV • N=100,000-10,000,000 high resolution • As comparison, HPLC N=1,000-20,000

  12. Zone Broadening • Single phase (mobile phase) - no partitioning • three zone broadening phenomena • longitudinal diffusion • transport to/from stationary phase • multipath • planar • no stationary phase • capillary • no stationary phase or multipath

  13. Transport • ions migrating in electric field • cations to cathode (-ve) • anions to anode (+ve) • Electroosmosis movement in one direction • anode (+ve) to cathode (-ve) • Components • Analyte dissolved in background electrolyte and pH buffer • Silica capillary wall coated with silanol (Si-OH) and Si-O- • Wall attracts cations - double-layer forms • Cations move towards cathode and sweep fluid in one direction • Electroosmotic flow proportional to V • usually greater than electrophoretic flow

  14. Bulk flow properties hydrodynamic ion buffer

  15. Techniques • Electropherogram • migration time analogous to retention time in chromatography • Isoelectric focusing • Gradient • No net migration • pH gradient with weak acid

  16. Techniques

More Related