Quiz 3 - Chromatography Flashcards
chromatography
a class of techniques used to separate components of a mixture based on physical property difference
3 types of chromatography
1) thin-layer chromatography (TLC)
2) column chromatography
3) gas chromatography
How are components of mixture separated?
- based on partitioning of molecules between 2 phases (stationary and mobile phase)
- polarity
- size
- volatility
stationary phase
- solid phase in TLC/column chromatogrphy
- liquid phase in gas chromatography
- often composed of silica (SiOx)
stationary phase types
- polar ==> referred to normal phase chromatography
- nonpolar ==> referred to as reverse phase chromatography
reverse phase chromatography
- modified silica
- hydroxyl groups can be functionalized with different nonpolar groups (carbon chains)
partition coefficient (Kp)
- defines the degrees of separation of the analytes (components of a mixture)
- Kp = (stationary phase)/(mobile phase)
mobile phase
- solvent phase for TLC and CC
- gas phase for GC
- pure solvent or mixture of solvents
- mobile phase moves through the stationary phase
Large Kp
- higher retention time
- x moves slower through stationary phase
- more polar molecule
Small Kp
- lower retention time
- x moves faster through stationary phase
- less polar molecule
TLC (thin layer chromatography)
- qualitative analysis
- requires a very small amount of material
TLC uses
- assess sample purity
- assess polarity
- establish compound identity
- monitor reaction progress
- monitor CC seperations
mobile phase moves through the stationary phase via…
capillary action
TLC set up
- mobile phase solvent
- filter paper to saturate atmosphere with solvent
- lid
- TLC plate
- draw baseline with pencil
different solvents result in different degrees of separation
- the more polar solvent allows for disruptions that create more separation than less polar solvents
retention factor (Rf)
- used to determine affinity of a compound for stationary phase
- [spot distance / solvent distance]
- high Rf = less polar
- low Rf = more polar
identifying compound with Rf
- different Rfs in the same solvent = different molecules
assessing sample purity
- multiple spots = impure
- one spot = pure
monitoring components of a reaction
- do different time intervals of a reaction sample to see spots appear/disappear to show products forming and reactants being used up
reading TLC plate
- UV light
- staining with potassium permanganate (oxidizing product)
unequal ratios of reactants may cause
multiple spots when some reactants did not get completely used up during the reaction
