3.16 Chromatography Flashcards
What are the basic principles of chromatography?
Seperation technqiues in which a mixture is separated if dissolved in solvent (mobile phase) and passed over a solid (stationary phase)
What is meant by the mobile phase?
Carries the soluble components of a mixture
What makes components move faster?
Solubility
Affinity to the solvent
What is meant by the stationary phase?
Holds back components of mixture attracted to it
How are substances separated by chromatography?
Balance between affinity for mobile phase and stationary phase different for every component meaning they move at different rates
Why will different substances show different Rf values?
Bonded differently and have different polarities
More polar bonds = smaller Rf value
Which phase are hydrogen bonding/dipoles attracted to?
Stationary phase
What does TLC stand for?
Thin Layer Chromatography
What is the stationary phase in TLC?
Plastic/glass/metal sheet or “plate” coated in silica or alumina
What are the advantages of TLC over paper chromatography?
Runs faster
Smaller amount of mixture required
TLC plates more robust
How can colourless spots be observed in TLC?
UV light
Developing agent (ninhydrin + heat)
How is Rf value calculated?
distance moved by component
÷
distance moved by solvent front
What does Rf value mean?
Retention factor
A ratio between rate of movement of solvent and component
How can the identity of a substance be confirmed by its Rf value?
Comparison with accepted Rf values for that substance run in the same solvent and set up
What is column chromatography?
Column packed with silica, alumina or resin has solvent run down through it
What is the stationary phase of column chromatography?
Silica, alumina or resin packed into column
What is the mobile phase in column chromatography?
Eluent
The solvent added at the top that runs down
What are the advantages of coumn chromatography?
Better separation as more than one eluent can be used
Fairly large amounts can be separated and collected
What is the stationary phase in gas-liquid chromatography?
Powder coated will oil packed into a long thin capillary tube that is coiled and placed in oven
What is the mobile phase in gas-liquid chromatography?
Carrier gas
What is measured in gas-liquid chromatography?
Retention time
Different mixtures taken different times to move through
What are the advantages of gas-liquid chromatography?
Very sensitive even to minute traces
What are the uses of gas-liquid chromatography?
Drugs testing
How can gas-liquid chromatography be used to identify substances?
Match gas chromatograph to that of a known substance in same conditions
Retention time should be an exact match
