Chromatography Flashcards
Chromatography
Used to separate mixture and identify them
Mobile phase = can move and either liquid or gas
Stationary phase = solid or liquid in solid support
Principles of chromatography
MP = goes through/ over the stationary phase
Distance each substance moves depends on the solubility of mobile phase and retention of stationary phase
Component more soluble will travel faster ( more adsorbed/ high retention less further travel
It’s these difference in solubility and adsorption that separates out the mixture
Thin layer chromatography
MP : liquid ( ethanol)
SP : thin layer of silica ( silicon dioxide) / alumina ( aluminium oxide ) on glass/metal plate
How thin layer chromatography works
- Draw a baseline using a pencil at end of the TLC plate, add small drop of mixture and let it dry
- Put the TLC place in the beaker containing small amount of solvent and cover the beaker with a lid ( the level of solvent needs to be lower than the baseline )
- Solvent will start to move up carrying the mixture ( some chemicals carried faster than others and so travel further )
- Pull out the TLC plate from the beaker once the solvent front is near top ( draw the solvent front with pencil before it dries )
- Let the TLC plate dry in the fume cupboard ( ensure toxic and flammable gas doesn’t escape )
- Result = chromatogram- the position of the chemicals on the chromatogram to identify the chemicals
Revealing colourless chemicals
UV light = TLC plate have special fluorescent dye that glows under UV light, put the plate under UV light = dark patches can be drawn around it with pencil
Iodine vapour = locating agent, chemical sticks to it leaving purple spots
( leaving the plate in a sealed jar with iodine crystals
RF Value
Distance travel by spot / distance travelled by solvent
- if change in TLC plate, solvent or temperature = can the value of Rf
Column chromatography basic
- mostly used to purifying an organic product ( separate for side product / unreacted chemicals)
SO : solid, absorbent material such as aluminium oxide coated with water - slurry
MP : solvent ( mobile phase) - let is run slowly and continuously
What happens in Column chromatography
As mixture is washed through the column = compo seep out depending on how soluble they are to mobile phase and how strongly they are adsorbed by stationary phase.
- longer spent dissolved = quicker it travel
- as compo of mixture reaches the end, it’s collected ( compo identified by time taken to pass through the column - retention time )
Gas chromatography
If have mixture of volatile liquids - can use GC to separate them out
Stationary phase = solid / solid coated by viscous liquid ( packed into long coloum)
- its coiled and built into oven
Mobile phase = unreactive carrier gas (nitrogen)
Sample is then vaporised and passes through the oven as gas
How gas chromatography works
Each component takes different amount of time form being injected into coloum to being recorded at the other end
- retention time depends on how much time spent the components spent moving along the carrier gas, and how much time it spent adsorbed in viscous liquid
- under standard conditions each component will have unique time & can use time to identify the component
- area under each peak tells you the relative amount of component that’s present in the mixture
What can GS be used for
Used to find level of alcohol in blood / urine - result accurate enough to be used as evidence for the court
- also used to find the proportion of various esters in oils used in paint - lets paint restores know what paint was used.
GC-MS
GC = used to seperate mixture into components
MS =used to identify components
- computers can be used to match up the mass spectrum for each component of the mixture against database, so whole process is automated.
Advantage of GC-MS over just GC
Components deprecated out by chromatography can be positively identified, which can be impossible from a chromatogram alone
Because some components have similar retention time
