i prepared a stock solution of Methanol: water extract of seeds of Abrus precatorius. The stock solution was prepared by dissolving the crude MeOH: H2O in 10% DMSO/ filtered water. i now want to run TLC and flash column on this fraction. I want to know how do i prepare my sample from the stock solution for TLC and Flash chromatography. Do i have to rota vap the stock solution and then dissolve in the eluting solvent or should i take the stock solution and simply dissolve in the eluting solvent?
I my experience water and DMSO will interfere with TLC. It would be best to prepare a fresh stock solution and not use the 10% DMSO. Better results will be obtained if you could evaporate (rotovap) away the water in your crude extract and just use methanol or a mixture of methanol and dichloromethane for spotting samples on a TLC plate when scouting out conditions for eventual flash chromatography. The water in the sample will interact with the CaSO4 binder used on the TLC plate and cause the spot to run as a streak or oddly shaped blob. When you spot the water methanol DMSO solution on the TLC plate it will take an excessively long time to dry and the DMSO will still remain. DMSO will interfere with some solvent systems giving results that are difficult to interpret and reproduce. It is best to spot a sample on a TLC plate in the least polar solvent (or solvent mixture) it can be dissolved in to keep the sample spot from spreading too far out at the origin.
For flash chromatography it is best to load your sample in the eluting solvent, you could always absorb your extract onto a small amount of the silica gel stationary phase and load it as a band on the top of the prepared column bed. Depending on your chosen solvent system the DMSO could come off the flash column and contaminate fractions that contain a compound of interest.
