Worldwide, 20% of deaths of children under 5 is due to water-related diseases. An effective way to disinfect water is chlorination, which is done by adding hypochlorite salts such as sodium hypochlorite. Sodium hypochlorite reacts with water to produce a strong oxidant, hypochlorous acid, that kills microbes. In water hypochlorous acid exists in equilibrium with a weaker oxidant, hypochlorite ion. The combined concentration of hypochlorous acid and hypochlorite ion is called free available chlorine (FAC). The relative concentrations of hypochlorous acid and hypochlorite ion determines the sanitization activity of added hypochlorite salts.
Hypochlorous acid (HClO), strong oxidant, main bactericidal agent
Hypochlorite ion (OCl-), weak oxidant, formation favoured at high pH
Significance of water (pH) monitoring: The relative concentrations of hypochlorous acid and hypochlorite ion is a function of pH. Thus, in addition to measuring FAC, it is important to monitor pH of water to judge the sanitization activity of added hypochlorite salts.
Current methods for pH measurement: Glass electrode is widely used to measure pH, but requires frequent calibration, has a long response time particularly for low ionic strength solutions, and is fragile. Some of these limitations have been overcome by the use of pH sensitive dyes with either flow injection analysis system or immobilised in a matrix. While the former does not allow continuous monitoring, the latter is not suitable for pH monitoring of solutions containing strong oxidants such as hypochlorous acid.
Our approach: TBA