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Chromatography

Chromatography. Chem 2411L Dr. Clower. Chromatography. Separation of components of a mixture Stationary phase Solid Liquid coated on solid Mobile phase (flow over stationary phase) Liquid Vapor Components distribute over phases based on affinity for either phase.

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Chromatography

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  1. Chromatography Chem 2411L Dr. Clower

  2. Chromatography • Separation of components of a mixture • Stationary phase • Solid • Liquid coated on solid • Mobile phase (flow over stationary phase) • Liquid • Vapor • Components distribute over phases based on affinity for either phase

  3. Types of Chromatography • Column Chromatography • Thin Layer Chromatography (TLC) • Paper Chromatography • Gas Chromatography (GC) • Mass Spectrometry (MS) • High Performance Liquid Chromatography (HPLC)

  4. Column Chromatography • Vertical glass column • Mobile phase = liquid • Pure solvent or mixture of solvents • Typically nonpolar → polar • Stationary phase = solid • Silica gel (SiO2) • Alumina • Sample = Solid or liquid placed on column

  5. Column Chromatography, cont. • Affinity = molecules adsorbed on solid • Compound in liquid elute first • More polar molecules elute last • Size • Collect separated compounds (fractions) • Evaporate solvent • ID or further purify

  6. Thin Layer Chromatography • Similar to column chromatography • Mobile phase = solvent • Chosen for polarity • Often mixtures • Trial and error • Stationary phase = solid (silica gel) • plastic or glass backing • Sample = spot on plate (1-2 mm) • Dissolve sample in volatile solvent • Drop with tiny capillary

  7. TLC, cont. • Solvent chamber • TLC Plate • Detect spots • UV lamp • Fluorescent dye in adsorbent layer • I2 vapor • Rf = distance spot moved / distance solvent moved • Compare Rf value to known sample on same plate

  8. Usefulness of TLC • To determine the # components of a mixture • To test fractions from column chromatography • To choose a solvent for column chromatography • To monitor a reaction • Does NOT tell you how much of each component is in a mixture

  9. Paper Chromatography • Similar to TLC • Stationary phase = H2O adsorbed by cellulose • Mobile phase = solvent • Frequently used for polar compounds • Amino acids, carbohydrates, etc.

  10. Gas Chromatography • Mobile phase = stream of inert gas • Stationary phase = high boiling liquid film • Polarity similar to compounds in mixture • Polymers • Supported on a solid • Packed in a column • Heated glass or metal • 2-3 m in length; 2-5 mm diameter • Sample = injection from syringe (1 mL) • Often add 1 mL air

  11. GC, cont. • Affinity = vapor vs. liquid • Separated components • Pass by detector • Send signal to electronic recorder • Can be collected for further analysis (rare) • Signal display = peaks • Area under peak = % of mixture • ½ b x h • Integrated • Massed on balance • Analysis • Retention time (min.), Area, % of mixture

  12. Gas Chromatogram • Retention time can be used to ID a component if compared to known sample under same conditions • Flow rate, column size, temperature, etc.

  13. MassSpectrometry • Used with GC • Break molecules into ions (fragments) M → M•+ + e- M•+→ A+ + X A+→ B+ + Y etc. • Gives mass of molecular ions, fragment ions • Plot relative abundance vs. mass to charge ratio

  14. Methyl Benzoate

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