Suppressed ion-chromatography using Na2CO3/NaHCO3as eluent was applied to the determination of chloride, sulphate, nitrate and bromide in highly mineralised waters. The effect of different concentrations of hydrogen carbonate on the retention times of the determination of the four selected anions was studied. Depending on the total concentration of ionic species, dilution of the sample is recommended to obtain retention times approaching those of the anion standard. The stability of sample composition was not affected by the presence of iron(III) ions (up to 15 mgL−1).