Hello, looking for alkaloids in my samples, I have stained my TLC with Drägendoff reagent. I have obtained dark orange and brown compounds (alkaloids) but also white spots. Does anyone have an explanation for the white spots, please?
Is it possible the white spots are where non-polar compounds ran? They would prevent the reagent from wetting the plate causing it to appear white. A water-spray is useful for detecting non-polar compounds that do not absorb UV, and so are otherwise invisible with the F254 flourescence.
Hello Mr. Bensaddek,
In my experience white spots on the TLC plate have been compounds that do not react with the revealing agent that I was using. I suggest you do a screening using different revealing agents (for example: http://scs.illinois.edu/hpl/tlc.php) to find more clues about the nature of your compounds, and if possible a quick IR spectra.
Best wishes.
Dear Lamine Bensaddek,
I agree with previous answers. But I want to add that if we are targeting alkaloids then the reaction will show dark brown color/yellow color spots. But some times the white spots appeared in TLC due to non-reactive spots with Dragendorf;s reagent. It will be more creative to find out these spots in your TLC. You can do some reactions with other reagents to find out the different category of compounds in same extract or mixture.
Good luck!!
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