Natural Product chemistry. With a sample being a hexane fraction, how much polarity should be changed while running a column?
I assume you are running a silica column. You shouldn't need much of a polarity change if it was extracted in hexane. I suggest running TLC plates which will suggest a suitable solvent system. Solvents to try include hexane/ethyl acetate, hexane/toluene, hexane/ether (diethyl ether or tetrahydrofuran).
In addition to silica columns/TLC plates, also try alumina and diol columns with the solvents mentioned above. diol bonded phases sometimes work very well with non-polar materials.
You will probably need to pack the column with a small amount of the strong (polar) solvent as the solvent adsorbs on the column as well and the compounds will elute later. If using an automated flash system, start the equilibration with 1-2% strong solvent and elute for at least 5 column volumes.
Dear john depending on the nature of compounds as exhibited by TLC profile you can decide polarity. But remember, you can't isolate in a single run unless and until it is a major compound. So, if you are targeting isolation in one shot you can adjust polarity increment by 5-% and if you want re-purification then you can adjust by 10% increment only when your eluent is say Hex:EtOAc or Benz:EtOAc for targeting sterols/terpenes lets say!
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