3.3.16 Chromatography

Where a column is used to seperate substances based on their properties Called High Pressure Liquid Chromatography (HGLC)

The sample is diluted into a diluent then added to the column The column is filled with beads The beads are coated with molecules (non-polar) The more non-polar the sample is, the more it sticks to the beads As the sample moves down the column, different substances move at different speeds When the sample reaches the bottom, a detector shines light through it Any molecules which absorb light show up and are measured by the detector

It groups substances with similar properties

They can change Some are polar and some are not

There is a heated long glass coil Gas is forced through the coil which forces the substance through The denser particles take longer to reach the detector The detector can be replaced by a mass spectrometer to determine the mass

If the attraction is too great between the substance and the beads, the sample can get stuck The diluent can be swapped from a polar to a non-polar one which can force the conditions in the column to change

Seperates substances based on size Column packed full of beads with channels in them The channels allow smaller molecules through Bigger molecules travel faster down the column as there is less space for them to move through The small molecules are slowed down because there are more spaces for them to stop

An aluminium plate with a silica matrix (solid phase) Draw a line in pencil along the bottom and place samples along it Dip the edge of the paper in the diluent (liquid phase) Solvent moves up through the plate The distance reached by the solvent is the solvent front Retention factor (Rf) = distance moved by spot / distance moved by solvent The Rf is the s

Retention factor (Rf) = distance moved by spot / distance moved by solvent The Rf is the same for each substance

Runs faster Smaller amounts can be seperated The spots usually spread out less The plates are more robust than paper

The mobile phase which carries the soluble components of the mixture with it. The more soluble the component, the faster it moves The stationary phase will hold back the components of the mixture that are attracted to it. The higher affinity for the stationary phase, the slower it moves

A sheet of glass covered in silica gel