Thin-Layer chromatography & column chromatography (10 pts) Why is the solvent ch

Question

Thin-Layer chromatography & column chromatography
(10 pts) Why is the solvent changed in the middle of the column separation procedure after the first analyte has passed through the column? 1. Give scientific reason!! 1 already know that "....i would not work if you don't change the solvent"! Hint: what physical property of the solvent is changed? 2. (10 pts) Once you start the chromatography column with liquid you cannot stop the flow (there is no valve!) It is essential that you do not let the column packing run dry! How do you maintain a steady and continuous flow throughout the separation procedure?

Explanation / Answer

1) during separation process we use less polar solvent first then we increase the polarity.

so the first anlayte separted will less polar then the next one.

If we will use the polar solvent (changed solvent) in the middle of column separation procedure, the polar solvent will be more adhered to silica gel (the column) then the next analyte (to be separted), so these occupied sites will not be available for the anaylte to adhere to silica gel and it will be in more contact with the solvent (the mobile phase) and hence will be easily and speedily seprated.

b) We have to refill the solvent regularly if we are not using pump.

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