HOCl Sensor Technology
Miniaturized amperometric sensors for chlorine monitoring
In short
HOCl–pH sensors combine technologies to accurately quantify hypochlorous acid levels in combination with information on pH. This enables monitoring of levels of acrive free chorine as well as total free chlorine.
Advantages:
- Real-time monitoring of both pH and HOCl
- Supports closed-loop control systems in water treatment
- Can be miniaturized for field use or embedded in smart systems
- Combination of amperometric sensor and ISFET offer non-glass, robust option
In detail
Hypochlorous acid (HOCl) is widely employed as a disinfectant in drinking water treatment due to its strong antimicrobial properties. It effectively inactivates bacteria, viruses, and other pathogens, ensuring that water remains safe for human consumption. Maintaining an optimal HOCl concentration is critical: insufficient levels can lead to microbial contamination, while excessive levels may produce undesirable taste, odor, and harmful disinfection by-products (DBPs) such as trihalomethanes.
Monitoring HOCl in drinking water is therefore essential for both public health and regulatory compliance. The concentration of HOCl depends on factors such as pH, temperature, and the presence of organic matter, which can influence its stability and disinfectant efficiency.
.Accurate and real-time detection methods, such as amperometric sensors, enable water utilities to control disinfectant dosing effectively, ensuring microbial safety while minimizing chemical overuse and potential health risks.
In aqueous solutions, chlorine exists mainly as:
- HOCl (hypochlorous acid) – the active disinfectant.
- OCl⁻ (hypochlorite ion) – dominates at higher pH.
- The balance depends on pH: HOCl predominates at pH 5–7; OCl⁻ dominates above pH 8.
- HOCl is more potent than OCl⁻, so monitoring HOCl specifically is important for assessing disinfectant efficacy.
How amperometric sensing works
An amperometric sensor is a type of electrochemical sensor that measures the current produced by a redox (oxidation–reduction) reaction of an analyte at an electrode. It is a miniaturized electrochemical cell consisting of a working-electrode (WE), a counter-electrode (CE) and a reference-electrode (RE). The HOCl concentration measurement is based on the electrical current generated by the reduction of HOCl at the working electrode at a fixed polarization voltage Vcell. The current is directly proportional to the concentration of the target substance.
Key components of an amperometric sensor:
- Working electrode (WE): Where the redox reaction occurs (e.g., platinum, gold, glassy carbon).
- Reference electrode (RE): Maintains a stable potential (e.g., Ag/AgCl). It does not pass current.
- Counter electrode (CE): Completes the circuit for current flow. It is set to the same potential as the reference electroe.
- Electrolyte or sample solution: Contains the analyte to be measured.
Advantages of amperometric sensing:
- Can be automated for continuous monitoring.
- High sensitivity – can detect very low concentrations.
- Rapid response – current changes immediately upon analyte presence.
- Quantitative – current is directly proportional to analyte concentration.
- Can be miniaturized for portable sensors.
Application
HOCl sensors support applications in water safety, healthcare, sanitation, and environmental protection, enabling intelligent disinfection management.
- Water Disinfection: Swimming pools, drinking water, and wastewater treatment.
- Food Processing & Sanitation
- Environmental Monitoring : Detects disinfectant byproducts and ensures water systems are not over-chlorinated or acidic.
Safe and efficient chlorine control
- Water disinfection monitoring
- Aquaculture water quality
- Environmental sensing
- Food processing hygiene
- Laboratory and medical disinfection control
- Chemical process supervision
