Hi
I synthesized something that looked like pale yellow oil.
In order to separate it from starting material, I did column chromatography.
As product loaded, the pale yellow color is dilluted and I can't see that.
So I used so many test tubes to get "transparent" liquid product. Fortunately, I got it using TLC but I think it is not efficient.
Is there any method to see which has no color product?
Best option will be to run your sample through HPLC (prep) or flash chromatograph (UV detection).
In the absence of these equipments you can run UV-Vis on the fractions colected in the test tubes. This involves that your compound of interest to absorb in a different region that the solvent used to eluate (check the UV cut off).
Other option will be to run the chromatography in a glass (transparent) column (if is done from quartz will be the best), a UV lamp, and UV protection glasses.While you are running the separation you can close the visible light in the hood and check with the UV lamp how the compounds are eluting.
The issue, as I see it, is you have a lot of fractions to evaluate. Marius mentioned using a flash chromatography instrument, but you didn't have one or else you'd have used it.
If you ran the column isocratically, one can estimate the time the compound came off from the retention factor (Rf) on TLC. The elution volume, as "column volumes" or CV = 1/Rf. If the compound has an Rf = 0.3, you look for fractions around 3 column volumes. You can estimate 1 CV as the "void" volume. The TLC is run using the same isocratic solvent mixture as the column.
If you have access to a mass spectrometer with an ASAP option, you can just take "dippings" from your fractions on a glass rod into the source and look for your compound. Sometimes, it will work even without an ASAP- you may find enough comes off sticking a capillary a into a regular electrospray or APCI to make a response.
You can run TLC plates on their edge and spot a lot of fractions, which can be run at once. Consider initially running every third fraction, and then testing the fractions on either end of your peak. TLC is faster than the HPLC mentioned above since many fractions are run in parallel, and one still needs to get the fractions into the autosampler vials.
I really appreciate you guys answers Jack, Qassim and Marius.
I'll try it these methods
Thank you again!
Dear Jack silver, can you please tell me, how can I see a spot of aliphatic cyclic compounds in TLC.
Adarsh Kumar , assuming the compounds are not volatile, you can try a water spray.This works because the compounds in the spots are hydrophobic, and prevent the silica underneath from being wetted. The result will be white spots on a gray background.
Develop the TLC plate, let the solvents evaporate, then spray with water. If there is too much spray, the water will flow under the spots and they can't be seen. Let the plate dry and try again later. Have a camera ready since the spots won't show for very long.
Help colleague, from your question you have challenge with the detection of your spots after column chromatography and TLC. Just view your TLC plate using short and long wavelength of UV lamp, it will fluoresce if it contains conjugated bond or you used universal spray reagent such as conc H2SO4 as well as specific spray reagent using spray gun if you have idea about the the class of compound, the spots will char the plate.
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