3.16 Chromatography

Question 1

how do you calculate retention factor?

Answer 1

distance travelled by component / distance travelled by solvent

Question 2

in TLC what is the stationary phase?

Answer 2

• thin layer of alumina or silica gel is coated onto glass, plastic or metal plate

Question 3

in TLC what is the mobile phase?

Answer 3

• liquid solvent
• moves up plate by capillary action

Question 4

in TLC how does seperation work?

Answer 4

• more polar compounds bind more strongly to silica gel and move slower
• less polar compounds travel faster with the solvent

Question 5

how can we locate spots in TLC

Answer 5

• UV light
• Ninhydrin
• iodine vapour

Question 6

how can we conduct a TLC analysis

Answer 6

1. prepare beaker with small amount of solvent
2. on a TLC plate, draw horizontal line at bottom ( baseline )
3. place a spot of reference sample on left of baseline, place spot of samples to be analysed on right of baseline, allow to dry
4. place TLC plate inside beaker, and close lid
5. as solvent reaches top, remove plate and draw another line where solvent has reached ( solvent front )

Question 7

in CCT what is the stationary phase?

Answer 7

• inert solid, usually powdered silica gel or alimina

Question 8

in CCT what is the mobile phase?

Answer 8

• liquid solvent used to carry mixture through the column

Question 9

in CCT what do i do with the sample mixture to be seperated?

Answer 9

• add to top of column
• use a pipette to carefully add this

Question 10

in CCT explain the different speeds.

Answer 10

• more polar compounds bind more strongly to stationary phase and move slower down column
• less polar compounds bind less and move faster with mobile phase

Question 11

in CCT what is meant by elution?

Answer 11

• components exit column at different times and can be collected seperately

Question 12

in GCT what is the mobile phase?

Answer 12

• inert gas that carries the sample through the column

Question 13

IN GCT what is the stationary phase?

Answer 13

• high boiling point liquid coated on inside of a long coiled tube

Question 14

what happens to sample in GCT before it starts

Answer 14

sample is vaporised in the injector and carried into column by gas

Question 15

in GCT what two factors affect speeds?

Answer 15

• boiling point, vaporise faster travel quicker
• solubility in stationary phase - more soluble, more time adsorbed and take longer to elute

Question 16

why do compounds have different Rf values?

Answer 16

• each compound has a unique affinity to solubility in stationary and mobile phases