Chromatography

Question 1

Mobile phase

Answer 1

Phase that MOVES in chromatography

Question 2

stationary phase

Answer 2

Phase that DOES NOT MOVE in chromatography

Question 3

Thin layer chromatography (TLC)

Answer 3

stationary phase- solid (silica mounted on glass plate)

mobile phase- liquid (suitable organic solvent)

separation by adsorption to the plate/solubility in the solvent

Question 4

Gas Chromatography (GC)

Answer 4

stationary phase- liquid (absorbed on an inert solid support)

mobile phase- gas (inert)

separation by relative solubility in the liquid stationary phase (solubility of the component)

Question 5

Retention factor Rf

Answer 5

Rf= distance moved by the component / distance moved by the solvent front

<1 (always decimals)

Rf values are compared to known Rf values in order to identify each component in the mixture

Question 6

Limitations of TLC

Answer 6

compounds with similar structure (e.g. stereoisomers) have similar Rf values so some components do not separate out

Question 7

Limitations of GC

Answer 7

•compounds with similar structures (e.g. stereoisomers) have similar retention times so some components do not separate out

•new or unknown compounds have no reference retention times for comparison

Question 8

Retention Time

Answer 8

time taken for a component to pass from the column inlet to the detector