What is the mobile phase?
Carries the soluble components of the mixture
What relationship between a sample and the mobile phase makes the sample move faster?
- More soluble components
- More affinity to the mobile phase
What does the stationary phase do?
Holds back components of the mixture that are attracted to it
What relationship between a sample and the stationary phase that make the sample move slower?
- More affinity for the stationary phase means that a sample move slower, often attracted by hydrogen bonding
How are substances separated by chromatography?
- If suitable stationary and mobile phases are chosen, the balance between affinity will be different thus they move at different rates
Why will different substances show different Rf values?
They are bonded differently and have different polarities
What would happen to the retention time if the polarity of the stationary phase and the compound are similar?
The retention time increases because the compound interacts stronger with the stationary phase - smaller Rf value
What is the stationary phase in TLC?
Plastic or glass sheet coated in silica
What are the advantages of TLC over paper chromatography?
- Runs faster
- Smaller amounts of a mixture can be separated
How can you observe colourless spots?
- Shine UV light on them
- Spray with a developing agent (turns colourless amino acids spots to purple, also requires heat)
How do you calculate the Rf value?
Rf = distance moved by spot/distance moved by solvent front
What does Rf value stand for?
Retention factor - a measure of the rate of the movement of a component through the chromatography apparatus
What is the stationary phase in gas chromatography?
High boiling liquid adsorbed onto an inert solid support
What is the mobile phase in gas chromatography?
An inert gas
How does gas chromatography work?
- A small amount of the volatile mixture is injected into the apparatus
- The mobile carrier gas carries components in the sample through the capillary column which contains the liquid stationary phase
- The components slow down as the interact with the liquid stationary phase
