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Conditions for separating anions by gradient ion chromatography are explored where detection is performed with the post-column addition of a solid-phase (SPR). Gradient ion chromatography can be useful when analyzing samples containing trace analytes in the presence of large amounts of a particular anion. However, loss of peak height and area of early eluting anions can occur when there is an extremely high concentration of a second later eluting anion. The distortion appears to result from a moving zone overloading of the separation column. Only early eluting anions are affected. The concentration dependence of the excess anion is studied and various approaches to mitigate the peak distortion are discussed.