chemistry TLC plate

Question

1)    Bob the chemist ran a TLC plate of his product, but the spot would not move off the baseline. The eluent he used consisted of a 30% polar / 70% non-polar solvent system.  Which solvent system should he try next in order to get the compounds in his product mixture to move up the plate?  (3 pts.)

(a)   10% polar / 90 % non polar

(b)   5% polar / 95% non polar

(c)   40% polar / 60% non polar

Answer 1

Since the product did not move off the baseline of the TLC plate, and since the mobile phase (eluent) is rather non-polar, this suggests that the product is rather polar. If the product were significantly non-polar, it would be eluted by the non-polar solvent and moved up the plate. Therefor, the next solvent system to use would likely be (c) 40% polar / 60% non-polar.

PS. Side note: It would be unlikely that the product didn't move at all off the baseline with 30% polar / 70% non-polar, and then significantly move using solvent system (c), but since this is a theoretical question, answer (c) would apply.