A method for the oxidation of ethylene to form ethylene oxide is provided that includes passing an aqueous stream through a guard bed and one or more ion exchange treatment beds. The guard bed and the aqueous stream contain from about 0.2 to 20 wt % ethylene glycol. The guard bed contains a cross-linked polystyrene resin, partially functionalized with quaternary ammonium functional groups and the resin has a surface area of greater than 400 m2/g.