33 chromatography
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what is chromatography?
separation techniques
what are the 3 things needed for every type of chromatography?
• stationary phase • mobile phase • mixture of 2 or more substances that need to be separated
what is a stationary phase?
solid substance that the mixture passses over
what is a mobile phase?
liquid or gas that is carried over the stationary phase
what are the mixtures separated due to?
different affinities to the stationary phase or differences in solubility
what happens if a component of the mixture has a high affinity to the stationary phase?
will travel slowly
what happens if a component of the mixture has a low affinity to the stationary phase?
will travel quickly
what happens if a component of a mixture is highly soluble?
will travel quickly with the solvent
what happens if a component of a mixture has low solubility?
will travel slowly with the solvent
what are 3 types of chromatography?
• thin layer chromatography (TLC) • column chromatography • gas liquid chromatography (GC)
what is the stationary phase in TLC?
thin piece of aluminium or glass coated in silica gel or aluminia
what is the mobile phase in TLC?
solvent
how is the mixture separated in TLC?
• mixture dropped at the bottom of the stationary phase • once separated and dry, examined under UV light/chemical reagents
describe the solubility and affinity for a component in TLC that has travelled further up
higher solubility lower affinity to the stationary phase
describe the solubility and affinity for a component in TLC that has travelled lower down
lower solubility higher affinity to the stationary phase
how can you identify the components in TLC?
by calculating Rf value
what does Rf value shhow?
how far a component has moved compared to the solvent front
what is the equation for Rf value?
distance moved by component/distance moved by solvent
what are 3 advantages for TLC?
• faster than paper chromatography • works on small samples • determines when a chemical reaction is complete
what are 5 limitations for TLC?
• similar compounds can have similar Rf values • conditions have to be the same to compare Rf values • new compounds have no reference Rf values • can be difficult to find a solvent that separates all components • can’t be used to separate large quantities
what is the stationary phase in column chromatography?
powder (silica or aluminia)
where is the stationary phase in column chromatography?
in a narrow glass tube with taps and spouts called a column
how is the mixture separated in column chromatography?
• mixture loaded onto the top of the column • a solvent is poured onto the top • different components collected at the bottom in separate beakers at different rates
what is the mobile phase in column chromatography?
solvent