What are the best ways to remove tetrabutylammonium impurities after a reaction with TBAF, TBAI, etc. I have a polar amino acid compound which after purification by silica gel column (10% MeOH/DCM) or reverse-phase HPLC (30-70% MeCN/H2O + 0.1% NH4OH) still contains a lot of some tetrabutylammonium impurity (probably as the hydroxide). It comes from a TBAF mediated OTBS deprotection that requires 3 eq of TBAF, which is why I get so much of the impurity.