3.3.16 Chromatography Flashcards
What is column chromatography?
Where a column is used to seperate substances based on their properties
Called High Pressure Liquid Chromatography (HGLC)
What is the process of column chromatography?
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
What results do you get from column chromatography?
It groups substances with similar properties
In column chromatography, what are the properties of the beads?
They can change
Some are polar and some are not
What is the process of gas chromatography?
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
What are the problems which can occur with the polar or non-polar nature of column chromatography?
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
What is size exclusion?
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
What is thin layer chromatography?
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
How do you calculate the Rf values?
Retention factor (Rf) = distance moved by spot / distance moved by solvent The Rf is the same for each substance
What are the advantages of thin layer chromatography over paper chromatography?
Runs faster
Smaller amounts can be seperated
The spots usually spread out less
The plates are more robust than paper
What are the two phases of chromatography?
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
What is a TLC plate composed of?
A sheet of glass covered in silica gel
