Chromatography Flashcards
Stationary phase
Solid substance
Mixture passes over in order to separated
Mobile phase
Liquid or gas
High affinity to stationary phase
Travel slowly
Low affinity to stationary phase
Travel quickly
Highly soluble in mobile phase
Travel quickly with solvent
Low solubility in mobile phase
Travel slowly with solvent
TLC diagram
https://www.chemguide.co.uk/analysis/chromatography/thinlayer.html
Stationary phase in TLC
TLC plate
Thin piece of aluminium/glass coated in silica gel
Mobile phase in TLC
Solvent/eluant
What condition allows spots to become visible in TLC?
UV light/iodine/fluorescent dye
RF equation
RF= distance moved by component/distance moved by solvent front
Advantage of TLC
Faster than paper chromatography
Works on very small samples
Disadvantage of TLC
Similar compounds may have similar Rf values
Cannot be used to separate large quantities
Column chromatography uses
Narrow glass tube with spout and tap- column
Stationary phase in column chromatography
Column packed with powder such as silica
Mobile phase in column chromatography
Solvent/eluant
How is the compound separated in column chromatography
Mixture and solvent run through column
Different components of mixture travel through stationary phase and once reached the bottom, can be collected into separate beakers
Advantage of column chromatography
Larger quantities can be separated
If there is a more polar compound, what would a more polar solvent mean?
Higher solubility to mobile phase
Travels quickly
If there is a more polar compound, what would a more polar stationary phase mean?
Higher affinity to stationary phase
Travels slower
Gas-liquid chromatography used to
separate complex mixtures of volatile compounds
Mobile phase in GC
Carrier gas e.g. nitrogen or helium
Stationary phase in GC
Solid/viscous liquid e.g. alkane, which lines the capillary column
Why can we only explain separation in terms of affinity to the stationary phase?
Mobile phase is not a solvent
How do we record distance travelled with gas chromatography
Retention time- time is takes from point of injection for component to detector
Limitation to GC
Lots of chemicals may have similar retention times and peak shapes so cant be positively identified
GC-MS
Enables separation of complex mixtures
AND
Identification of each component of that mixture
Uses of GC-MS
Forensics
Airport secuirity
Why do we wear plastic gloves holding TLC plate?
Essential – to prevent contamination from the hands to the plate
Why do we add developing solvent to a depth of not more than 1cm3?
Essential – if the solvent is too deep it will dissolve the mixture from the plate
Why do we allow the solvent to rise up the plate to the top?
Not essential – the Rf value can be calculated if the solvent front does not reach the top of the plate
Why do we allow the plate to dry in a fume cupboard?
Essential – the solvent is toxic
Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their Rf values.
Spray with developing agent or use UV
Measure distances from initial pencil line to the spots (x)
Measure distance from initial pencil line to solvent front line (y)
Rf value = x / y
