Hi,
I performed a silica gel column chromatography. At the final step, I used 100% methanol to elute all the rest. After evaporation, the dried layer on the glass flask can not be complete dissolved.
Firstly, I tried with 100% methanol but it didn’t work. Then I used dH2O which could dissolve a part of these dried compounds. I tried with 80% methanol and water but it also didn’t work.
I have two questions.
1. why do the compounds that eluted in methanol can not be dissolved again in methanol?
2. What should I do to completely dissolved the dried compounds?
If you know something, please give me a clue.
Thank you so much.
A few comments:
You did not provide any information about your sample type(s) so we do not know what their potential solubility may be. Perhaps temperature is the key? Gently warm the methanol / water solution (depending on the pressure used during chromatography, some heat may be generated). 50/50?
There is also the possibility that you have some raw silica gel in your solution (not sample, silica). Silica will not dissolve in Methanol so would be expected to appear in the final solution. I often see students contaminate their solutions with silica gel during crude extractions (esp low pressure runs). Once you properly dissolve your sample into solution (100%), you can easily filter out the remaining silica gel.
Hi William,
Thanks for your comment. I apply the extract from ethyl acetate fraction on the column. I've just started with this field so I don't know much about required information to tell you.
I incubated the flash and methanol in water bath at 40oC but it seemed not have any difference.
I found an article that mentions whether or not methanol dissolves silica gel, and I think silica gel beds that using in the column is hard to be dissolved in methanol. You can read it at https://selekt.biotage.com/blog/does-methanol-really-dissolve-silica-during-flash-column-chromatography
Your compound may be having water labile groups like -NH2, -OH or moisture sensitive moiety.
whenever doing the column purification of such kind compound , please add 0.1% TEA .
if you are using more quantity of aqueous Ammonia solution ,methanol will carry the water molecule along with your compound , then you will be getting distillation or evaporation problems.
Pease check your vaccum pump condtition
Trung, please go back and read my reply. I did not say that methanol will dissolve silica. " Silica will not dissolve in Methanol". Sometimes it forms a slurry, but it does not dissolve. You may in fact have silica in your sample so 'treating it' will not make it go away. Filter it off.
Hi William,
it's happens some of the molecules, such kind of the compounds doesn't ionize properly or its may be complex mol molecules, so, we have to choose high polar solvents like DMSO, DMF.
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