I have tried a host of solvent systems to resolve some fractions I eluted from a column on TLC plates to no avail. The fractions were eluted with Pet ether 90% and ethyl acetate 10%. I have used this same system to run the TLCs and have even added chloroform to the combination but the components will just not resolve. Can anyone suggest a solvent system that may help in resolving the components on a TLC?
Most of methanol extracts contains polar compounds and some oils /glycosides.,gums etc.( you can separate some compounds easily by extracting concentrated methanol extract with other solvents )
Most commonly used TLC solvent system are combinations of Acetone/EtoAC with Hexane/CHcl3.
Best way to identify suitable solvent system is ....apply a very diluted spot of extract at the center of a circular thick filter paper with a narrow capillary tube and try to apply with another capillary tube various solvents. The sports resolve circularly and give you a better idea for selecting TLC solvent system.
u shd not use Pet ether as it is a combination of hydrocarbons. Try Hexane:Ethylacetate 1:1 combination. If u observe any tailing u can add a small drop of formic acid.
Try Hexane:Ethyl acetate 8:2 or 7:3. But in the TLC plate , where is the spot?? up or down the plate, because you can try with combinations of ethyl acetate and acetone.
Solvent system always depends on polarity of your compound so you have to cross check for solvent system.Add few drops of acetic acid,or change the polarity by adding methanol in ratio Hexane:Ethyl acetate:Methanol in 6:3:1
1.Try reverse polarity..ie.based on the solvents used in the column for the fraction collected.
2.Try different types of TLC plates. (alumina /silica gel 254 etc.)
3.which ever solvent provides Rf 0.5 is the best one for the separation of spots (the fraction your are interested in)
@Bilal Zargar: I will try that combination and give you the feedback.
@Armando Torres: The spots are mostly up the plate even with Pet ether: Ethyl acetate 4:1. I think a combination of ethyl acetate and acetone will therefore be too polar and move all the spots to the solvent front.
@Tejinder Singh Oberoi: The last time I added methanol to my solvent system, the separation was not too good. All the spots moved with the solvent front and I could hardly distinguish between the spots. I'll try the hexane: ethyl acetate though.
Some of the fractions I collected with Pet ether 100% are showing blue spots on the plates under long UV wave i.e. 365nm. I wonder whether the blue fluorescence represents just oils or it may be a compound.
What is the nature of the material You eluated from? Is it product of synthesis or native material? It may help solve the problem.
The material is a concentrated methanolic extract of a plant.
Most of methanol extracts contains polar compounds and some oils /glycosides.,gums etc.( you can separate some compounds easily by extracting concentrated methanol extract with other solvents )
Most commonly used TLC solvent system are combinations of Acetone/EtoAC with Hexane/CHcl3.
Best way to identify suitable solvent system is ....apply a very diluted spot of extract at the center of a circular thick filter paper with a narrow capillary tube and try to apply with another capillary tube various solvents. The sports resolve circularly and give you a better idea for selecting TLC solvent system.
Dr.Chakravarthy...kindly elaborate the protocol of applying various solvents individually or in different random combinations,you detailed in last two lines...and how to identify the correct solvent system...
Dr.Sunita... the method of using thick filter paper technique is to save time, solvents and TLC plate cost for the initial expt.
1. Use solvents in increasing polarity scale (pet.ether.....to methanol).
2.The spot at the center of paper will show different spot expansions in circular way.
3.Best way to identify a solvent system is by trial with combination of one most resolving solvent with non resolving one.
4.In the initial phases by using small TLC plates (12mm by 5 mm cut plates and small 25 ml beaker with lid to hold 2-4 ml solvent and TLC plates exposed , will save solvents exp. and time. needless to specify the applied spots to be above solvents) .
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