Author Question: A mixture of compounds is spotted on a TLC plate and developed in 90:10 hexane:ethyl acetate. ... (Read 36 times)

renzo156 · **on:** Aug 23, 2018

A mixture of compounds is spotted on a TLC plate and developed in 90:10 hexane:ethyl acetate. Visualization with both UV and iodine shows a single spot at the origin. What mixture of hexane and ethyl acetate should you try next? Explain.

Question 2

Why is it a problem to have the spotting line on a TLC plate below the solvent level in the developing chamber?

Brenm · **Reply #1 on:** Aug 23, 2018

Answer to Question 1

You should increase the polarity of the solvent system by increasing the concentration of ethyl acetate, for example, to 90:10 ethyl acetate:hexane. The compounds are all polar and are adsorbed strongly onto the polar stationary phase. A significantly more polar mobile phase should be used to move the compounds with the mobile phase. A more polar solvent with more similar intermolecular forces will help dissolve the compounds into the mobile phase. In addition, the more polar solvent will help displace the compounds from the stationary phase because there are more mobile phase molecules than there are molecules of the compounds being analyzed.

Answer to Question 2

If the spotting line is below the level of the solvent in the developing chamber, significant amounts of the spotted material will dissolve in the solvent and be removed from the TLC plate.