Hi, Im currently doing TLC of plant crude extract by using chloroform: diethyl ether: methanol as solvent instead of chloroform: ethyl acetate: methanol from attached article. Im getting different result from the article and its confusing me because I know that both polarity of diethyl ether and ethyl acetate are bit different. I got 0.68, 0.3 and 0.24 retention factor which are diff than the article. But somehow i got the same colour as the spot on tlc from the article. Can anyone help me to interpret the result or suggest some journal article that can help me to identify compound based on solvent i used?
Another question is does essential oil only can be separated by toluene:ethyl acetate? Can i just use the same solvent (chloroform: diethyl ether: methanol )to separate essential oil? Actually I got multiple black spot from using the same solvent under 365nm UV light. Thanks.
Even if you used the same solvent, there is a good chance that your mobility (migration) values will be slightly different from those published by someone else. Variations in temperature, thickness of the plate coating, etc., can all influence mobility on TLC. That is why the recommended procedure is to compare mobility with a standard compound. With carbohydrates, we often use glucose, and report mobility as Rglc, that is, mobility relative to glucose. Even more useful would be comparing your spots to those of authentic compound, if you can get some from the authors of the paper. With these things considered, then slight variations, or even major changes, in solvent conditions will not matter as much.
I agree with @Greg. you should run standards. The retention will be different in your case because of the different solvents used. Using old vs a freshly opened package of TLC plates can also make a difference due to adsorption of water. TLC plates from different manufacturers also have slightly different chemistry (pH, moisture content) and adsorption characteristics (particle size, pore size) whic could lead to slightly different retention.
Yes I agree with you, standards are required and used as control for the TLC experiments, and it is not necessary to have the same results RF of a previous paper because as mentioned earlier the experiment conditions will be different.
Rf values are dictated by the solvent systems and cannot authentically be used to for structure determination unless you are only doing qualitative analysis. I suggest you do co-spotting with the standard if it is available. For essential oils, these are non-polar compounds and any non-polar organic solvent can be used: e.g Pet ether, n-hexane with ethylacetate (10-20%). Regards, Angeline
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