Chromatography
Made using the OCRChemistry A2 textbook. Pages 76-79. Gent and Richie.
- Created by: Former Member
- 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.
- Different components= different affinities for SP and MP.
- Stationary phase- fixed in place. Mobile phase- moves in definite direction.
- MP sweeps over SP.
- 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.
- Phases
- 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
- Analytical techinique used to separate the componants in a mixture
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