Determination of Sulfate Ion in Natural Water Involving a Large Amount of Ferric and Ferrous Ions

The end point of titration in the quantitative determination of sulfate radical by use of sodium rhodizonate as an indicator was obscure and disturbed by the presence of large amount of iron. Removal of iron and the other disturbing cations was effected by passing the solution through cation exchanger, Amberlite IR-120 of R-H form and the effluent was titrated with clear end point and with error of +2.6%. The result of using this method on a strongly acidic mineral spring agreed well with that obtained by gravimetric method.