The thermometric titration of sulfate is based on the exothermic precipitation reaction of barium sulfate. A standard solution of Ba2+ is used as titrant, which is added at a constant rate to the phosphoric acid. Once all sulfate has been titrated, the temperature of the sample decreases, indicating the endpoint.
Industrially, the procedure has been applied to the determination of sulfate in wet process phosphoric acid. This Application Bulletin describes the analysis for phosphoric acid (liquid fertilizer samples). For solid fertilizer samples, see Application Bulletin AB-307.
