The Dionex IonPac ATC and Dionex IonPac ATC 500 Anion Trap Columns contain microporous anion-exchange resin in the hydroxide form. The anion trap columns strip trace anionic contaminants out of the eluent and/or deionized water and prevents them from reaching the guard or analytical columns. Anionic contaminants present on the eluent and/or deionized water often interfere with the precision of trace anion determinations in particular when performing an anion-exchange application that involves a gradient eluent.