I wanted to elute n-hexane-soluble fraction of a plant extract in a silica gel column using different proportions of dichloromethane/n-hexane. The bands separated visibly initially but moved only a very short distance down the column and get bound to the silica. A little ethyl acetate moved the bands down but mixed them together. (1). What suggested solvent system can separate the compounds better. (2). What is the possible nature of the compounds in the extract?
It depends on the size of your column and the weight of your extract, but anyway, try to increase the elution solvent volume and decrease the rate of elution. Try a mixture of hexane: chloroform with different ratios (TLC outside first). You may have steroids or terpenes (search on the previously published articles related to your species if it’s not new). You can also do preparative TLC with several runs.
Read about Normal phases liquid chromatography. Everythin will be clear.
So everything relatively polar will be strongly retained on silica gel when n-hexane is used as eluent. Add 10-30% of isoproanol - you will remove it. If not - add more or use 100% isopropanol, THF, DCM/MeOH etc.
Regards
GB
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