Chromatography Flashcards
What is chromatography used for?
To separate stuff in a mixture to be able to identify the components
What is the mobile phase?
Where the molecules can move
What phases are involved in the mobile phase?
Always a liquid or a gas
What is the stationary phase?
Where the molecules can’t move
What phases are involved in the stationary phase?
Must be a solid or a liquid on a solid support
What is the basic principle of the chromatography?
The mobile phase moves through or over the stationary phase.
The distance each substance moves depends on its solubility in the mobile phase and its retention by the stationary phase
What happens to components that are more soluble in the mobile phase?
They will travel further than components which are more strongly adsorbed to the stationary phase
What is the mobile phase in TLC?
Solvent such as ethanol
What is the stationary phase in TLC?
A thin layer of silica or alumina fixed to a glass or metal plate
Why must the solvent be below the baseline?
So it doesn’t dissolve the samples
What is the solvent front?
how far the solvent has travelled
Why does the plate have to be placed in a fume cupboard in TLC?
To prevent any toxic or flammable fumes from escaping into the room
What are the two ways of revealing colourless chemicals?
- UV light
- Iodine vapour
How do you reveal colourless chemicals using UV light?
Many TLC plates have special fluorescent dye added to the silica or alumina layer which glows when a UV light Is shined on it and then circles can be drawn around the dark spots of chemical
How do you reveal colourless chemicals using iodine vapour?
It is a locating agent so it sticks to the chemicals and shows them up as purple spots
What do you use to identify chemicals?
Rf values
What is the equation for calculating Rf values?
distance travelled by spot / distance travelled by solvent
How do you calculate the distance travelled by spot?
Measure from the centre of the spot to the baseline
How do you calculate the distance travelled by solvent?
Measure from the solvent front to the baseline
What do you do once you have your Rf value?
Compare it to data to identify the component
What is column chromatography?
Mostly used for purifying an organic product
What does column chromatography involve?
Packing a glass column with a solid adsorbent material such as aluminium oxide coated with water (slurry)
What is the stationary phase in CC?
Solid adsorbent material
What is the mobile phase in CC?
A solvent which is run slowly and continually down the column
What happens when the mixture is run through the column?
It’s components separate out according to how soluble they are in the mobile phase and how strongly they are adsorbed onto the stationary phase (retention)
In CC, what happens the more soluble a component is in the mobile phase?
The quicker it’ll pass through the column
