Dear Zheng Ju,

Did you consider using ion-exchange resins? This could be done by the application of a mixed bed (anion and cation) exchanger. First one should wash the resin with toluene, to avoid so-called bleeding (dissolution of non reacted or soluble resin material). Next the resin is dried and added to your reaction product, gently mixed for several hours and finally the resin is removed by filtration. The big ion-exchange resin manufactirers should be able to advise what kind of product you could use for your application.

I hope this is helpful!

Kind regards, Leo