Chromatography Flashcards
2 phases in chromatography
Mobile phrase
Stationary phase
What is the mobile phase
Substrate that allows molecules to move through the stationary phase. It can be in form of liquid or gas depending on what type of chromatography is being carried out
What is the stationary phase ?
Which the mixture passes over in order to be separated. Made from a thin piece of aluminium or glass coated in silica gel
The mixture can either be separated either due to …
Different affinities/retention to the stationary phase
Different solubility in the mobile phase
Different affinity / retention to the …
Stationary phase
Different solubility to the….
Mobile phase
High affinity to the stationary phase means
Travel slowly
Lower affinity to the stationary phase means
It will travel quickly
High solubility to the mobile phase means
It will travel along quickly with the solvent
Low solubility to the mobile phase means…
It will travel slowly with the solvent
TLC - thin layer chromatography
Add solvent to a beaker which is the mobile phase and our the lid on so no evaporation of the solvent which is also called elutant.
Draw a pencil line in the TLC plate like 1cm above the bottom and add dot samples using a capillary tube at equal lengths.
Place the TLC plate in the beaker and out in above the solvent. Solvent draws up the stationary phase depending on retention/ affinity and solubility. Take out the TLC plate before it reaches the end of the plate and line of the plate Plate is examined under UV light or chemical to see the position the samples and allow to dry
Rf = retention value
Distance moved by sample /distance moved by solvent
Column chromatography
- Uses a narrow glass tube with a spout like a burette which is called the column.
- The column is packed with a powder such as silica to act at the stationary phase
- mixture is loaded on top of the column
- a solvent is poured on top of the column and soaks down the stationary phase. When u open up the spout This solvent is the mobile phase
- The different components will travel down depending on solubility and affinity
- They will travel at different rates
- One will reach the bottom and can be collected into a big first and the next will be collected into a separate beaker sometime later
Advantage of column chromatography
Larger quantities can be separated
Why does the column need to be wet at all times?
If it runs dry and cracks, it can cause mixing of bands
Gas chromatography
Used to separate volatile components( substances that can easily evaporate eg gases )
The mobile phase is a gas known as the carrier gas and is typically an unreactive gas such as nitrogen or helium
The gas flows through a long thin tube known as a capillary tube which is coiled up
The sample to be separated is injected into the column. The carrier gas transports the components of the mixture along the column at different rates causing them to separate out.
as the mobile phase is not solvent you cannot say component separate due to different. solubilities. you can only say that they separate in terms of affinity to the stationary phase
A liquid stationary phase is a high molecular mass alkane with a high boiling point. Silicone polymers can be used as solid stationary phase in gas chromatography. The lower the affinity to the stationary phase the higher of the volatility. And the stationary phase can be changed to suit the mixture to be separate
