Free vs. Total Chlorine

Free chlorine is the combination of Cl₂, HOCl, and OCl^-. Combined chlorine is formed when ammonia is added to free chlorine, yielding chloramines (mono-, di-, tri-, organic). Total chlorine is the combination of free and combined chlorine in solution.

For applications that contain no ammonia, a free chlorine measurement is appropriate. For applications where ammonia or chloramines might be present (e.g. wastewater and drinking water), a total chlorine measurement is appropriate.

The main difference is which probe you will use. The Kuntze Zirkon® DIS is for a free chlorine measurement, and measures the presence of only HOCl. The Kuntze Zirkon® DIS Total (right sensor shown) measures the presence of both HOCl and OCl^-, which allows the analyzer to give a total chlorine measurement.

Be sure your reference measurement is configured to measure the correct parameter, and that you have purchased the correct reagents to do so. The free chlorine measurement works best below pH 8.5, while the total chlorine measurement is capable of going up to pH 10. If you have any further questions, please contact a Kuntze representative.