I am isolating compounds from plant extract from a Petroleum ether fractions. There is some compounds in the elution of 5% Ethyl acetate:95% Petroleum ether fractions as clumped and it is hard to purify even in less polar fraction of 3%. How to isolate such compounds using silica column. Please give me suggestion.
- Try using pet-ether/toluene for a solvent system. Toluene is less polar than ethyl acetate.
- Very non-polar compounds sometimes do not adsorb well on silica because it is very polar. Try alumina. Also try diol or cyano bonded phases, these can be run as normal phase with normal phase solvents.
Kumaravel Kaliyaperumal , You should try Hexanes/toluene or Hexanes/DCM instead of a system with Ethyl acetate because your PE fraction comprises of very non-polar compounds. Use TLC to see how the suggested system help in resolving the mixtures before you transfer it to the column.
I will suggest that you give silver nitrate impregnated silica gel column a trial If you did not obtain the desired resolution on TLC after various trials of different ratios of the said solvent systems.
Good luck with your experiment.
Silver nitrate impregnated silica gel is normally used for the separation of unsaturated compounds, wherein the tendency of silver [most probably silver(I)] to form reversible bonding with a C-C double bond is utilised for the separation.
What Ayorinde Victor Ogundele and Jack Silver have mentioned, appears to be quite plausible. Yes, ethyl acetate is relatively too polar for this separation. You may try n-pentane/diethyl ether mixtures with varied proportions. I have used this solvent pair extensively for various separations.
You may also try flash chromatography (FC). This is better than normal classical column chromatography (CC) in many ways. FC is faster, more efficient in separation when compared to CC.
PLEASE TAKE CARE OF SAFETY ASPECTS WHILE CARRYING OUT FC AS THIS INVOLVES APPLICATION OF PRESSURE ON THE SOLVENT NORMALLY USING A GAS UNDER PRESSURE.
With best wishes,
ARB
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