Final answer:
For a compound soluble in DMF and water but not in organic solvents, a polar TLC eluent system such as a mixture of methanol, ethanol, or acetonitrile with water is advised. Start with a less polar mixture and increase polarity as needed for separation. Buffering the aqueous phase may help maintain solubility.
Step-by-step explanation:
If the prep-LC is broken and you need to purify a compound with two carboxylic acid groups, one amine, and one amide bond, and if the compound dissolves well in DMF and water but not in other organic solvents, selecting a suitable TLC eluent system could be challenging.
In this case, since the compound is polar due to the presence of carboxylic and amide groups, a polar solvent system would be necessary. A combination of solvents such as methanol, ethanol, or acetonitrile with water could be a starting point.
To determine the best ratio, you may need to perform TLC trials, starting with a less polar mixture and gradually increasing the polarity until effective separation is achieved.
Considering the solubility properties, utilizing a mixture of DMF or water with a polar organic solvent, like methanol or ethanol in the eluent system, might work. You might also explore using a buffered aqueous phase to help solubilize your compound’s ionizable groups, potentially using a buffer like acetate or phosphate at a suitable pH to maintain solubility.
For visualizing your TLC, a staining agent or UV light, if your compound or impurities have chromophores, will be necessary. However, to give you the most appropriate advice, it would be helpful to know more about the polarity and other properties of your compound.