Chromatography

Made using the OCRChemistry A2 textbook. Pages 76-79. Gent and Richie.

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  • Created by: M
  • Created on: 19-12-12 17:32
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  • Chromatography
    • Analytical techinique used to separate the componants in a mixture
      • Can separate out components with very similar properties in complex mixtures
      • After separation, the pure components can be analysed precisely
    • How does it work?
      • Phases
        • MP sweeps over SP.
          • Different components= different affinities for SP and MP.
            • SP interacts with components of mixture. Greater interaction= slowed more.
        • Stationary phase- fixed in place. Mobile phase- moves in definite direction.
      • Separation
        • Liquid SP separates by relative solubility. (dissolve more readily= slowed down more)
        • Solid SP separates by adsorption. Components bind to surface of solid SP.
    • Thin-layer Chromatography
      • SP= an adsorbent (SiO2/Al2O3) coated on a support (glass/plastic)= TLC plate
      • MP= liquid
      • Chromatagram
        • Visible record of result of separation
        • Dissolve sample, sample spot on TLC plate allow to dry, into jar with solvent layer below spot, seal,  separation by adsorption, may need locating agent
      • Limitations
        • Similar compounds= similar Rf
        • Unknown compounds= no reference Rf
        • Difficult to find suitable solvent/ mixture of solvents
      • Rf Values
        • (distance moved by component) / (distance moved by solvent front)
        • Compare with pure compounds to identify unknowns

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