Chromatography pt 2

Chromatography pt 2

1. Rf Value

   • If spots on the chromatogram are colourless you have to use a locating agent
   • Distance travelled by solute / distance travelled by solvent
   • If the Rf values are the same value the substances may be the same

2. Gas chromatography

   • If the substance being tested is not already a gas it needs to be vapourised
   • The mobile phase is an unreactive gas such as nitrogen and the stationary phase is a thick liquid
   • The unknown miture is injected into a long tube coated on the outside with the stationary phase. The mixture moves along with the mobile phase until it comes out at the other end. The time it takes a chemical to travvel through the tube is called retention time. The retention time is different for each chemical. The chromatogram for gas chromotography is a graaph. The distance along the x axis is the retention time and eahc peak is a different chemical