15E.3

Question 1

what are the two refinements of column chromatography

Answer 1

1. High performance liquid chromatography (HPLC)
2. gas chromatography

Question 2

what are the main differences between the HPLC and column chromatography

Answer 2

1. the solvent is forced through a metal tube under pressure, rather than being allowed to pass through it by gravity
2. the particle size of the stationary point is smaller, which leads to better separation of the components
3. the sample is injected into the column
4. the components are detected after they pass through the column by their absorption of ultraviolet radiation
5. the whole process is automated, and the results are quickly available on a computer display

Question 3

how is the HPLC set up

Answer 3

page 138

Question 4

what is the retention time

Answer 4

(in HPLC AND GC) the time taken from the injection to detection

Question 5

What does the retention time depend on

Answer 5

1. the nature of the solvent
2. the pressure used
3. the temperature inside the column

Question 6

what are the main differences between the gas chromatography (GC) and column chromatography

Answer 6

1. the metal tube can be serval meters long and it can be coiled up to save space
2. the stationary phase is a solid or a liquid coated on the inside of the tube
3. the mobile phase is an inert carrier gas (N or He)
4. the sample is injected into the column
5. components passing through the column are detected
6. the whole process is automated, and the results are quickly available on a computer display

Question 7

how does a GC set up look like

Question 8

what is an inert gas

Answer 8

a gas that doesn’t undergo many chemical reaction like noble gases and nitrogen

Question 9

how is the mixture separated in GC

Answer 9

after the sample is injected the components vaporize and they move through the coil with the carrier gas, they will move at different speeds, according to how strongly attracted they are to the stationary phase, more attraction slower speed sower retention time

Question 10

for an absorption against time graph the area under the peaks is

Answer 10

the relative concentration of the components

Question 11

what is the one advantage that column chromatography has over HPLC and GC

Answer 11

it can collect reasonable amounts of components

Question 12

how are the GC components detected

Answer 12

they are detected in a flame (so they are destroyed)

Question 13

how is the relative concentration of different components displayed on a graph

Answer 13

page 139 (absorption x time)