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Posted: Thu Jun 26, 2008 6:51 am
by HW Mueller
Whatever it is it´s not MeOH directly (no primary MeOH reaction), maybe there could be some viscosity (mechanical) effect involved?
Posted: Thu Jun 26, 2008 6:57 am
by danko
Hi Usv,
Why should dissolved silica result in cloudy fractions?
If the solubility of silica is favored in the column, what would disfavor it in the test tube?
Best Regards
Posted: Sat Jun 28, 2008 3:10 am
by usv
Not really sure what is causing this. Flushing out fines seems the most likely. There does seem to be some solubility component with methanol and normal phase. When fractions are concentrated and resuspended wit out methanol, we can filter out the particulates. With reverse phase too we have observed where once the methanol is removed there is additional precipitate in the remaining aqueous. In this case we have considered whether itis the C18 componenet that is leeaching out. MPLC and flash silica are of lower grade.
Posted: Sat Jun 28, 2008 8:49 am
by HW Mueller
In our lab we have also seen this partial redissolution problem quite often. It is surprising what dirt (other than deteriorated stat. phase) can come off a column after a bit of use. Sometimes the mobile phase leaves a "footprint".... Once in a while I wanted to know whether these "stubborn" precipitates are organic or inorganic. There is a simple test with a crucible lid and a Bunsen burner: Most inorganics leave ashes behind on the hot ceramic. Sometimes one gets a flame color test this way also.