CL 29- chromatography

Question 1

stationary phase for TLC

Answer 1

silica gel supported on plastic firm

Question 2

mobile phase for TLC

Answer 2

organic or aqueous solvent

Question 3

stationary phase for GC

Answer 3

high boiling point liquid on inert solid support

Question 4

mobile phase for GC

Answer 4

inert gas e.g. nitrogen

Question 5

what happens in the stationary phase?

how do the components move

Answer 5

• interacts with the components in the mixture, slowing them down
• greater affinity with st. phase, slower the component moves

Question 6

what happens in the mobile phase?

Answer 6

components allowed to move over the stationary phase at different speeds

Question 7

how to undergo chromatography

method

Answer 7

1. draw a baseline in pencil on TLC plate
2. sample spot on baseline
3. place in beaker with solvent (solvent underneath baseline)
4. LID NEEDED (solvent would evaporate)
5. wait until solvent front is close to the top BUT NOT REACHED TOP and draw a pencil line before it drys

Question 8

how to develop chromatogram

Answer 8

• hold under UV light to view spots, draw round spots in pencil
  OR
• spray with developing agent
  then calculate Rf values

Question 9

Rf

calculation

Answer 9

distance from the baseline to the spot / distance from the baseline to the solvent front

Question 10

how does TLC separate the components of the mixture?

Answer 10

the components adsorb into the stationary phase, bind with different strengths so have different speeds

Question 11

how does gas chromatography separate

Answer 11

by relative solubility in the stationary phase

Question 12

retention time

definition

Answer 12

characteristic of the compound under given conditions

Question 13

how does volatility and retention time relate?

gas chromatography

Answer 13

compounds that have a high affinity for the mobile phase emerge first (are most volatile) and have a low retention time
produces peaks

Question 14

what does GC produce and what do these things tell us

Answer 14

1. retention time- identifies the unknown by comparing to databases
2. peak integration- tells you how much of the substance is present in the mixture

Question 15

uses of GC

Answer 15

• very sensitive so detects small quantities of substances (explosives, drugs)
• separation of pure substances for collection
• can be connected to mass spectrometer for direct identification of substances