6 - Chromatography

Question 1

What is the purpose of chromatography?

Answer 1

for separating a picture into its components or compounds and identifying the substance

Question 2

In TLC - why do some components not move as far as others?

Answer 2

Components with stronger intermolecular forces will absorb more strongly to the plate surface and not travel as high up

Question 3

Rf value calculation

Answer 3

Rf = distance travelled by a component / distance travelled by the solvent

Question 4

2 limitations of TLC and Rf values

Answer 4

1. Many substances have a similar Rf value so compound can’t be identified uniquely
2. New compounds may not have an Rf value at all

Question 5

How does a gas chromatogram work?

Answer 5

• Uses a gas to carry the compounds of a mixture through separating column
  2. Components separated by absorption to internal solid surface of column, each comes out individually
  3. Amount of each component is measured and shown on gas chromatogram along with retention time
  4. Pure samples of each compound obtained, sent to mass spec, identified from its unique fragmentation pattern

Question 6

Retention time definition

Answer 6

The time it takes for one component to travel through the separating column

Question 7

Calculation - proportion of one compound

Answer 7

(area under peak A / total area under all peaks) x 100

integration value = area