- 4 Tlc Plates Are Useful In Developing Separation Methods To Be Applied To Column And Or Flash Chromatography Analogo 1 (144.45 KiB) Viewed 41 times
- 4 Tlc Plates Are Useful In Developing Separation Methods To Be Applied To Column And Or Flash Chromatography Analogo 2 (69.7 KiB) Viewed 41 times
4. TLC plates are useful in developing separation methods to be applied to column (and/or flash) chromatography. Analogous to the relative component retention measured as Rf on TLC plates, retention on columns can be characterized by CV, the number of column volumes of solvent needed to elute the components. Three different solvent mixtures were tested in a TLC system and on a flash liquid chromatography column, using the same stationary phase for both. The solvent fronts were allowed to migrate to the same level on the TLC plates for each test, as shown: (lmage from ww. blotage.com) a. If you wanted to separate A and B, collecting each fraction as it was eluted from a column, which solvent mixture would give the "cleanest" separation (minimal cross-contamination between A and B ? How do you know? b. Which fraction (A or B) will be collected first i.e. which will elute from the column first? How do you know? c. All else being held constant, if the solvent mixture is changed, is the order of elution always the same? Why or why not?
d. Tabulated the data on Rf and CV, using same mobile and stationary phase: What is the mathematical relationship between Rf and CV? How do you know? e. For all tests, the ΔRf values are very similar, 0.10 to 0.13, but the absolute Rf values vary more. Give a physical basis for the observation that solvent mixture #3, with the smallest absolute Rf values, but largest CV values. (Hint: What does a small Rf value tell us about the attraction between the solute and the stationary phase or the solvent?)