this would be a basic extraction. in steps, acidify the impurity with acid to form a water soluable salt. extract with acidic water and organic solvent (how bout CH2Cl2). The impurity is in the aqueous phase because the salt is water soluable, so isolate the organic phase. repeat a few times and combine organic phases from each step, then rotovap to isolate your purified compound. THis is all assuming that your compound is non basic, and is soluable in non polar solvent.