Chromatography

Question 1

What is the definition of retention time

Answer 1

Time taken from injection until a component reaches the detector

Question 2

What is the stationary phase of paper chromatography

Answer 2

Water absorbed

Question 3

What is the mobile phase of paper chromatography

Answer 3

Liquid solvent

Question 4

What should you do if the components of a paper chromatogram are colourless

Answer 4

Spray with a locating agent

Eg ninhydrin

Question 5

What is the Rf equation

Answer 5

Distance moved by spot
———————————
Distance moved by solvent

Question 6

When is two way paper chromatography used

Answer 6

To separate substances with similar Rf values

Question 7

What is the stationary phase of thin layer chromatography

Answer 7

Layer of adsorbent particles

Eg aluminium or silica (TLC plate)

Question 8

What does it mean when a substance is adsorbed

Answer 8

When it adheres to the surface

Question 9

What is the mobile phase of thin layer chromatography

Answer 9

Liquid solvent

Question 10

What is the stationary phase of gas liquid chromatography

Answer 10

High bp liquid or oil

Held on finely divided inert solid eg alumina/silica

Question 11

What is the mobile phase of gas liquid chromatography

Answer 11

Pure inert carrier gas

Eg N2

Question 12

How does gas liquid chromatography work

Answer 12

Gaseous sample mixed w inert gas
Components separate - partition themselves between mobile and stationary phase
More soluble in stationary phase - stay in coiled column longer
Components come out at different times

Question 13

How do you work out the relative concentration of a component in gas liquid chromatography

Answer 13

Area under peak
————————
Total areas for all peaks

Question 14

What is the method for running a paper/TLC chromatogram

Answer 14

1. Prepare concentrated solution of mixture
2. Mark origin line in pencil at bottom
   X in middle of line
3. Apply conc. solution to middle of X
   Using capillary tube
   Allow solvent to evaporate
4. Place paper/TLC in solvent
   Allow to run until solvent close to top
5. Mark solvent front
   Allow to dry
6. Develop using developing agent

Question 15

Describe the method for analysing paper/TLC chromatography

Answer 15

1. Mark centre of each spot
2. Distance from centre of spot to origin
3. Distance from solvent front to origin
4. Calculate Rf value

Question 16

Describe the method for two way paper chromatography

Answer 16

1. Prepare a concentrated solution of mixture
2. Mark origin line in pencil near the bottom and another at 90° to this near edge of paper
3. Apply concentrated solution at intersection
   Allow solvent to evaporate
4. Place in solvent
   Run until solvent close to top of paper
5. Rotate through 90°
   Run in different solvent
6. Develop using developing agent

Question 17

Describe the method of analysing two way paper chromatography

Answer 17

1. Mark centre of each spot
2. Measure distance from centre of spot to origin
3. Measure the distance of the solvent front from the origin
4. Calculate Rf
5. Repeat for second solvent
   And a second Rf value