Question

1. Describe the differences between paper chromatography and TLC. Give two advantages and two disadvantages of each method for analysis.

            

2. In order to prepare for a column chromatography separation of 3 ink dye components, you have run a TLC experiment with three possible solvent mixtures. These are the results:

1. Acetone:Hexane in 1:1 ratio gave the following distances: solvent=4.2cm, pigment #1=3.8cm, pigment #2=1.7cm, and pigment #3=1.3cm
2. Acetone:Hexane in 2:1 ratio gave the following distances: solvent=4.3cm, pigment #1=3.8cm, pigment #2=2.1cm, and pigment #3=1.4cm
3. Acetone:Hexane in 4:1 ratio gave the following distances: solvent=4.1cm, pigment #1=3.7cm, pigment #2=2.85cm, and pigment #3=1.8cm

By calculating the Rf values for all three scenarios, which solvent mixture would you choose as the mobile phase for the separation of the same pigments in a column chromatography analysis.

             

Answer 1

Differences : (1) stationary phase in TLC is thin layer of silica or alumina where staionary phase in paper chromatography is Paper.

(2) TLC gives better separations than paper chromatography, in TLC  bands that are sharper and more space are there.

(A) Advantages of Paper chromatography

1:- Cost-effective method.

2:-It can identify both organic and inorganic compounds

Disadvantages

1:-It can not separate complex mixture

2:- it can not save data for long time

(B) Advantages of TLC

1:-It can separate complex mixture

2:- it can separate very less quantity of sample

Disadvantages of TLC

1:-only applicable for soluble mixture compounds

2:- it is a Qualitative analysis, not quantitative analysis.

solvent 5 Rf-96 a distance travelled by pigment. bo distance travelled by solvent So for al a 3. 8cm b= 4, 2cm Rf, = al Rf, = 3.8 Ogos - 4.2 4.2 Rent 12 0.405 Rfz= a.2 1.3 = 0.309 4.2 b=4.3cm Y & for b) Real - 9 = 3.8 cm RS: 38 0.884 Rs 2.1 -0.488 4.3= 0.326 ( Data Rounded off)

X10 for mixture a Rea ar a, a 3.7 b= 4.1 R$ = 3,7 = 0.902 41 41 Rf = 2.35 = 0.695 R&z= 1.8 0.439 4.1 (ARE) So as you can see that for mixture 'a Rg Values are more spaced It means this solvent can separate well. (mobile phase) so I will choose à as the mobile phase