3.16 Chromatography

Question 1

What are the basic principles of chromatography?

Answer 1

Seperation technqiues in which a mixture is separated if dissolved in solvent (mobile phase) and passed over a solid (stationary phase)

Question 2

What is meant by the mobile phase?

Answer 2

Carries the soluble components of a mixture

Question 3

What makes components move faster?

Answer 3

Solubility
Affinity to the solvent

Question 4

What is meant by the stationary phase?

Answer 4

Holds back components of mixture attracted to it

Question 5

How are substances separated by chromatography?

Answer 5

Balance between affinity for mobile phase and stationary phase different for every component meaning they move at different rates

Question 6

Why will different substances show different Rf values?

Answer 6

Bonded differently and have different polarities
More polar bonds = smaller Rf value

Question 7

Which phase are hydrogen bonding/dipoles attracted to?

Answer 7

Stationary phase

Question 8

What does TLC stand for?

Answer 8

Thin Layer Chromatography

Question 9

What is the stationary phase in TLC?

Answer 9

Plastic/glass/metal sheet or “plate” coated in silica or alumina

Question 10

What are the advantages of TLC over paper chromatography?

Answer 10

Runs faster
Smaller amount of mixture required
TLC plates more robust

Question 11

How can colourless spots be observed in TLC?

Answer 11

UV light
Developing agent (ninhydrin + heat)

Question 12

How is Rf value calculated?

Answer 12

distance moved by component
÷
distance moved by solvent front

Question 13

What does Rf value mean?

Answer 13

Retention factor
A ratio between rate of movement of solvent and component

Question 14

How can the identity of a substance be confirmed by its Rf value?

Answer 14

Comparison with accepted Rf values for that substance run in the same solvent and set up

Question 15

What is column chromatography?

Answer 15

Column packed with silica, alumina or resin has solvent run down through it

Question 16

What is the stationary phase of column chromatography?

Answer 16

Silica, alumina or resin packed into column

Question 17

What is the mobile phase in column chromatography?

Answer 17

Eluent
The solvent added at the top that runs down

Question 18

What are the advantages of coumn chromatography?

Answer 18

Better separation as more than one eluent can be used
Fairly large amounts can be separated and collected

Question 19

What is the stationary phase in gas-liquid chromatography?

Answer 19

Powder coated will oil packed into a long thin capillary tube that is coiled and placed in oven

Question 20

What is the mobile phase in gas-liquid chromatography?

Answer 20

Carrier gas

Question 21

What is measured in gas-liquid chromatography?

Answer 21

Retention time
Different mixtures taken different times to move through

Question 22

What are the advantages of gas-liquid chromatography?

Answer 22

Very sensitive even to minute traces

Question 23

What are the uses of gas-liquid chromatography?

Answer 23

Drugs testing

Question 24

How can gas-liquid chromatography be used to identify substances?

Answer 24

Match gas chromatograph to that of a known substance in same conditions
Retention time should be an exact match

Question 25

What is GCMS?

Answer 25

Gas Chromatography-Mass Spectrometry

Question 26

How does Gas Chromatography-Mass Spectrometry work?

Answer 26

Gas chromatography is run, retention time recored
Mixture run through mass spectrometer
Fragmentation patterns confirms identity