Question

1. Several different combinations of solvents have been used for TLC so far. For example, 80% ethyl acetate/20% hexanes was chosen for the TLC separation of analgesics. Consider that solvent for the following questions.

a. Is it important that the solvents are miscible? Briefly explain why or why not.

b. Briefly explain what would be different if the ratio was flipped (i.e., 80% hexanes).

c. Would 100% hexanes have made a good solvent? Briefly explain why or why not.

d. Was the stationary phase used polar or non-polar?  

[Professor forgot to give answer key for study guide]

Answer 1

Solution:

Part 1(a)

The solvent should be in a good position to form a miscelle to carry the solute in separation possible, for the formation of miscelle the sovent should be miscible for the chromotgraphic condition. If the solvent is not miscible then the solute will not separate and resides in the state it has been dissolved

Part 1(b)

The ratio must always be under the norms of 1 and can be flipped at various propotions based on the experimental need.

Part 1(c)

The precaution must be taken while preparing the solvent ratio as 100% solvent will not elute the solute to the desired level,also the quality of separation will be affected as solvent are volatile in nature.

Part 1(d)

The stationary phase in chromotographic separation is always non-polar for quality solute elution, if not the eluted solute gets dissolved with stationary phase.