Question

The pigment was added to the first column (A-E) using 90:10 hexanes/ethyl acetate. The pigment was added to the second column as its original acetone extract. Both columns were then run according to the lab manual, starting with 90:10 hexanes/ethyl acetate as the eluent. Explain what impact the choice of solvent for loading the compound onto the column may have had.

Answer 1

Step-by-step explanation:

1st case:

B- the mixture starts separating.

C- non-polar impurity gets eluted.

D- gradual elution picture where all components are getting separated & purified.

E- last compound elution happening.

Loading pigment with a 10% EA-Hexane solution would lead to excellent separation of compounds from the mixture, evident from the column elution.

2nd case:

B- the mixture starts separating.

C- non-polar impurity gets eluted.

D- yellow & green component mixture is getting eluted.

E- last compound elution happening.

Since extra acetone was added in the elution process, solvent polarity got changed. Acetone (Dipole moment 2.69) is more polar than EA ( Dipole moment 1.88). Overall solvent polarity went up as Acetone got mixed in 10% eluent. Since the yellow component is more polar than green, that's why a 10% mixture can easily purify them. But greater than the suitable polarity of the solvent led to an overlap of those layers as yellow component interacted more with more polar solvent & traveled greater distance, causing junction to vanish & inevitable overlap. Also, later yellow bands broadened, resulting in a greater chance of overlap & impure mixture elution.