What type of solvent ration is appropriate for the isolation of low polar compounds from hexane fraction of plant extract by traditional silica(60-120 mesh) packed column chromatography?
Usually, we try to perform TLC before doing column chromatography. When we get a good separation in TLC then the same solvent strength can be used in CC.
For TLC you can use hexane and ethyl acetate in a ratio starting from 20:1 or 10:1 with increasing ethyl acetate.
A mixture of hexane and diethyl ether is also good. But diethyl ether is highly volatile, so evaporate rapidly and the ratio changes continuously.
For more follow these answers: https://www.researchgate.net/post/Solvent_system_for_Thin_Layer_Chromatography_of_non_polar_extracts
To separate low polar compounds, you can use pet ether or hexane as well. The problem is a lot of chlorophyll will appear in the extract if you use plant part having chlorophyll (steam and leave). Best solvent for separation is flashing with pet ether and then hexane and a ratio of hexane and methylene chloride and so on. Based on TLC behaviour, you can choose what to do next. In most cases hexane: methylene chloride is best choice for tlc. Thanks
I would try the following solvents systems:
hexane: ether
hexane: dichloromethane
hexane: toluene
hexane: ethyl acetate
Petroleum ether, cyclohexane, or heptane can be substituted for hexane
Non-polar compounds sometimes run poorly on silica gel because it is very polar. In a similar fashion to non-polar compounds not mixing with water, such compounds don't adsorb on silica well. You can try alumina or diol bonded-phase, run with the solvents listed above. Also, consider non-aqueous reverse-phase. It is reverse phase C18, but using organic solvents. For example, A= methanol, B = dichloromethane. For some examples of this, see:
https://www.teledyneisco.com/en-us/liquidChromatography/Chromatography%20Documents/Posters/Facile%20Isolation%20of%20Carotenoid%20Antioxidants%20from%20Solanum%20Iycopersicum%20Poster.pdf
https://www.teledyneisco.com/en-us/liquidChromatography/Chromatography%20Documents/Application%20Notes/Non-Aqueous%20Reverse%20Phase%20with%20RediSep%20Rf%20Gold%20C18%20App%20Note.pdf
Another suggestion for TLC of non-polar samples is use n-hexane/AcOEt (8:2 ), (7:3) , CHCl3/MeOH (9:1) or CH2Cl2/MeOH (8:2). These systems are, normally, efficient in routine experiments - with extracts of triterpenes, flavonoids and steroids, for example. Roni Roy
Regarding to TLC system, depending on the isolated compounds in the different extracts. If the compounds separated for first time and you haven't reference, start from non polar and gradually mix with polar solvent in different ratio..
10-0.0, 9-1, 8-2 ,7-3........etc till you get accepted Rf.
Study on TLC first..then try on different concentration of solvent polarity.
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