Chromatography_1

Chromatography_1

1. Thin layer chromatography

   • In TLC, the stationary phase is a solid and the mobile phase is a liquid.
     • A solid stationary phase separates by ADSORPTION. As the mobile phase passes over the stationary phase, component molecules are able to bind to the solid making up the stationary phase. This happens at the surface of the stationary phase.
   • Rf values= shows how far a components has moved compared with the solvent front.
     • Rf= Distance moved by component/Distance moved by solvent front.
   • The stationary phase is a thin layer of an ADSORBENT such as silica gel or alumina coated on a flat, inert support usually a sheet of glass or plastic.
   • A sample of the mixture is dissolved.
     • A small spot of the sample solution is placed on the TLC plate a short distance from one end of the plate. It is useful to draw a pencil line as a guide.
       • The sample spot is allowed to dry and the TLC plate is then placed in a jar containing a shallow layer of the solvent (mobile phase). The solvent must be below the sample spot. The jar is sealed to saturate the space in the jar with the solvent vapour. This slows down the evaporation of the solvent from the TLC plate and prevents solvent loss.

2. Gas chromatography

   • In GC, the stationary phase is a liquid or a solid on a solid support, and the mobile phase is a gas.
     • A liquid stationary phase separates by relative solubility.Some components dissolve more readily in the liquid and these are slowed down more than components with lower solubility.
   • RETENTION TIME is the time for a component to pass from the column inlet to the detector.
   • The mobile phase is a carrier gas which moves through the chromatography column. An inert or unreactive gas such as helium or nitrogen is usually used.

3. During chromatography, a MOBILE PHASE sweeps a mixture over a STATIONARY PHASE.

4. The stationary phase is fixed in place

5. The mobile phase moves in a definite direction

6. Chromatography works on the basis that different components have different AFFINITIES for a stationary phase and for a mobile phase.

   • The stationary phase interacts with the components in the mixture, slowing them down. The greater the interaction, the more the components are slowed down.
     • This allows different components to flow over the stationary phase at different speeds, therefore separating the components