Question

. What are the main characteristics of the mobile and stationary phases in gas

chromatography?

(10)

2. What are the main applications and advantages of temperature programming in GC? What

is the equivalent procedure in HPLC?

(20)

3. What is the purpose of derivatization in HPLC?

(10)

4. The following retention were measured in a column of 1.10 m:

air : 18.0 s.

methyl acetate: 1.98 min.

methyl propionate: 2.24 min

methyl n-butyrate: 7.93 min.

The base width of the three peaks were of 0.19, 0.23 and 0.79 min, respectively.

Calculate a) the number of theoretical plates in the column N

b) the equivalent height of a plate H

c) the length the column should have to obtain a resolution (Rs) of 1.5

for the acetate and the propionate

(20)

5.

Name two general methods for improving the resolution of two substances on a

chromatographic column.

(10)

6.

The distribution constant for compound X between n–hexane and water is 9.6. Calculate

the concentration of X remaining in the aqueous phase after an aliquot of 50.0 mL of

0.150 M of X has been treated by extraction with the following quantities of n-hexane:

(a)

One 40.0-mL portion;

(b)

Two 20.0-mL portions;

(c)

Four 10.0-mL portions;

(d)

Eight 5.0-mL portions.

What conclusion can you make from these calculations?

(20)

7.

Describe the principle of separation in a column used for size – exclusion

chromatography. What is the separation range in term of molecular weight? Give the

definition of “gel filtration: and “gel permeation

Answer 1