Topic 33: Chromatography Flashcards
Mobile phase
The mobile phase could be a gas or a liquid. It carries any soluble molecules with it as it moves.
What determines a samples speed in chromatography?
The greater the affinity/ solubility a molecule in the mixture has in the mobile phase, the faster it will travel.
The greater the affinity of a molecule to the stationary phase, the shorter the distance it moves with the mobile phase.
Think of it moving with the mobile phase and being pulled back by the stationary phase.
Stationary phase
The stationary phase in chromatography is the substance that the mixture is passed through. It can be a solid or liquid, and its properties (e.g. polarity) are chosen to selectively interact with the different components of the mixture.
Chromatography
Chromatography is an analytical technique used to separate and identify component molecules of a mixture. It uses a mobile phase and a stationary phase.
Rf
Different for each component molecule
Distance moved by component/ distance of solvent front
ALWAYS LESS THAN ONE
TLC stationary phase
Silica mounted on glass plate
TLC mobile phase
Suitable organic solvent
TLC separation
Solubility in mobile phase
Affinity in mobile phase moved further or less than other molecules
TLC limitations
Components can have similar Rf values
The unknown substance has no previous chemical to compare with as all Rf values are compared to database to identify
Column chromatography stationary phase
Silica - packed in column
Column chromatography mobile phase
Suitable organic solvent
Separation of column chromatography
Interact with the stationary phase to different extents
How Column chromatography works
Column packed with silica and solvent.
Mixture added on top
Tap opened allowing solvent to flow
Components travels at different rates
Batches of solvent collected which is evaporated leaving different samples of the different components.
Gas-liquid chromatography stationary phase
Liquid adsorbed on an inert solid support
Gas-liquid chromatography Mobile phase
Gas
How gas-liquid chromatography works
Sample injected to machine, sample boils, is carried along column by gas, contains liquid stationary phase which has adsorbed into an inert solid.
Time taken to travel through tube is called the retention time and depends on how much time is spend moving with gas rather than being attached to the liquid.
GLC retention time
Time taken for compound to travel through column to detector. time injected to peak height formed.
GLC retention time what makes it long
High boiling point and greater solubility to stationary phase makes longer retention time
GCMS
Gas chromatography Mass Spectrometry - Mass spec attached at end more accurate.
Lid
Needs to be there so doesnt evaporated so can have saturated chamber.
What if colourless in chromatography?
Use a developing agent like spraying ninhydrin on it - turns amino acids purple- or shine uv on it.
