Simultaneous flow-injection measurement of hydroxide, chloride, hypochlorite and chlorate in Chlor–alkali cell effluents

A flow injection method is reported for the simultaneous determination of hydroxide, chloride, hypochlorite, and chlorate ions that exist in Chlor–alkali cell effluents in concentrations ranging from sub-millimolar to several molar. The hydroxide concentration is determined by the heat of neutralization of the injected sample into an acidic carrier stream and the chloride concentration is calculated from the measured conductance data. For the measurement of hypochlorite and chlorate, colorimetric iodometry is used. Iodide is oxidized to iodine by OCl− and ClO3− in acid solutions. While room temperature is sufficient for the reaction between OCl− and I−, the reaction between ClO3− and I− requires an elevated temperature. The different reaction requirements are utilized to differentiate between NaOCl and NaClO3, respectively.