. What are the main characteristics of the mobile and stationaryphases in gas

chromatography?

(10)

2. What are the main applications and advantages of temperatureprogramming 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 1.10m:

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 0.79min, respectively.

Calculate a) the number of theoretical plates in the columnN

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 twosubstances on a

chromatographic column.

(10)

6.

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

the concentration of X remaining in the aqueous phase after analiquot of 50.0 mL of

0.150 M of X has been treated by extraction with the followingquantities 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 ofmolecular weight? Give the

definition of “gel filtration: and “gel permeation