Question

Remeber how you learned that a pure liquid distills within a narrow boiling point range, but that narrow boiling point doesnt necessarily imple a pure liquid? Keeping that lesson in mind, explain this: you know without a doubt from spectroscopic technique that your product mixture contains 2 distinct products... yet your TLC plate shows only one spot. How is this possible? The, your research advisor tells you thats its really not that unusual to encounter this kind of conflicting data and that it is often easily resolved with a little more bench work. What should you do to clear up the issue using the TLC?

Answer 1

The appearence of single spot (even though it is a mixture of product) in TLC plate mainly depends on the interaction of solute and the solvent (mobile phase) or the solute and the stationary phase. If the solute or compound is polar in nature and have more affinity towords the stationary phase than the mobile phase. In such cases, the high polar mobile phase has to be used to elute the compound. Always, to get a better identification of spots in TLC plates is suggested to use the mobile phase of less polarity to high polarity with the gradual variation of composition of solvents. In the above case, elute the TLC two to three times with less polar or nonpolar mobile phase (Hexane) to check weather the spots are distingushed, if the spots are not distingushed then slightly rise the poarity of mobile phase (Hexane: ethylacetate in the ratio of 0.9:0.1; 0.8:0.2; .....etc) to get distigushed spots in the TLC. Thereby, one can clearup the issue using the TLC.