Interferences of a barium ion-selective electrode used for the potentiometric titration of sulphate

Certain cations and anions interfere with the potentiometric titration of sulphate with barium chloride as titrant and a barium ion-selective indicator electrode. Thus, cations, for example potassium, which can be sensed by the barium ion-selective electrode, give distorted titration curves, while pH values below 1.5 lead to electrode breakdown. Cations, such as calcium, which interact with sulphate give low sulphate recovery, while anions that interact with the barium titrant lead to apparently high sulphate.Treatment of samples with cation-exchange resins in the sodium form can remove cation interferences, but acidification to pH 2 with hydrochloric acid prevents interference from anions, such as phosphate, carbonate-hydrogen carbonate and organic anions.