Question

Describe the effectiveness of the extraction method in terms of recovery.

Answer 1

(i) If you extract a compound (1 g) from the aqueous layer (water, 50 mL) into the organic layer (ethyl acetate, dichloromethane, etc, 60 mL) only once, you will recover a certain amount of compound.

Let the partition coefficient of a compound between water and an organic solvent (K) = 10

i.e. Final amount of compound in aqueous layer = {Vw/(Vw + K*Vo)}ⁿ * initial amount of compound in the aqueous layer

i.e. Final amount of compound in aqueous layer = {50/(50 + 10*60)}¹ * 1 g = 0.077 g

Therefore, the compound recovered = 1 - 0.077 = 0.923 g

(ii) If you extract a compound (1 g) from the aqueous layer (water, 50 mL) into the organic layer (ethyl acetate, dichloromethane, etc, 30 mL) twice, you will recover a certain amount of compound, which is more than the single extraction.

Final amount of compound in aqueous layer = {50/(50 + 10*30)}² * 1 g = 0.020 g

Therefore, the compound recovered = 1 - 0.020 = 0.980 g

(iii) If you extract a compound (1 g) from the aqueous layer (water, 50 mL) into the organic layer (ethyl acetate, dichloromethane, etc, 20 mL) thrice, you will recover a certain amount of compound, which is more than the double extraction.

Final amount of compound in aqueous layer = {50/(50 + 10*20)}³ * 1 g = 0.008 g

Therefore, the compound recovered = 1 - 0.008 = 0.992 g

Hence, the order of compound recovery: triple extraction > double > single.

i.e. 0.992 > 0.980 > 0.923