Titration Method for Measuring Chlorate Ion in Concentrated Bleach Solutions

The minimization of bleach loss is a high priority for sodium hypochlorite producers. The largest source of bleach loss during production is process related with the subsequent formation of chlorate ion.

The most accurate measurement method for determining the chlorate ion concentration in bleach is ion chromatography (IC). Because this measurement requires specialized equipment and training, most bleach producers are unable to measure the chlorate ion concentration (and the subsequent bleach loss) at the production site. Thus, a titration method has been developed for on-site use to estimate the chlorate ion concentration in 10-15% bleach solutions.

The titration method is based on the method proposed by Aieta, Roberts and Hernandez (AWWA, 1984, 76(1):64). The bleach sample is prepared by removing the available chlorine by reaction with hydrogen peroxide. The measurement is based on the titration of iodine by sodium thiosulfate. At pH2, a number of oxidizing species in the sample are titrated (e.g. chlorite ion). Under highly acidic conditions, chlorate ion is titrated along with the oxidizing species titrated at pH2. The chlorate ion concentration is calculated by taking the difference of the titrations.

This method is to be used for chlorate ion concentrations between 1,000 - 10,000 mg/L.

More Information

Additional Information Contained in this document includes:

  • Chemistry Background
  • Sample Preparation
  • Measurements
  • Calculations

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