Chlorine (Cl2) is strong oxidizing agent and ideal disinfectant. Proper residual chlorine levels in drinking water ensure that water is safe for human consumption, but too much chlorine can have detrimental effects in pharmaceutical production, membrane treatment processes and other applications.
Proper measurement and monitoring of residual chlorine levels helps to mitigate these risks. Whether you're working in a laboratory or in the field, Hach® provides a variety of chlorine analyzers, sensors, reagents and more that help offer simple and reliable measurements that you can trust.
Both lightweight and durable, Hach portable chlorine instruments provide reliable, hassle-free, on-the-go measurement in even the most challenging conditions.
Whether you’re treating utility water, product water, or wastewater discharge, Hach’s online chlorine analyzers deliver accurate and reliable measurements of free or total residual chlorine.
Whether you’re using the DPD, amperometric or iodometric method, we offer a wide range of reagents for easy and precise chlorine measurement.
Get fast results for free or total chlorine testing with kits available for a variety of applications including drinking water and pool water.
Highly adaptable to handle a variety of applications and parameters, Hach sensors and controllers ensure accurate and efficient chlorine measurement
When added to water, chlorine reacts to form free chlorine or chloramines (when ammonia is present), which:
Since chlorine can be detrimental, there are applications that require "dechlorination." Adsorption dechlorination uses activated carbon to remove chlorine compounds. Chemical dechlorination uses reducing agents such as sulfites, bisulfites or metabisulfites to destroy chlorine species.
During pre-oxidation, source water entering a plant is dosed with chlorine (pre-chlorination) to precipitate out minerals as a primary treatment step (besides disinfection) to help with suspended and dissolved matter removal before filtration. The water is then filtered to improve clarity and chlorinated again.
For chlorine to be effective, its concentration before and after filtration (as well as pH, water temperature, and contact time) must be monitored and controlled. Most treatment plants have a contact chamber (clear well) where chlorine is injected, mixed and allowed to remain in contact with the water for the required time dependent on the temperature, pH and type of microorganisms present in the water. The contact time provides a chlorine residual, intended to maintain water sanitized as it enters storage tanks and travels throughout the distribution system.
All chlorination before (pre-chlorination) and after filters (post-chlorination) is controlled at multiple points throughout the treatment process and in the distribution system. Additional booster chlorination of tap water in the network is usually conducted at pump/booster stations and must be thoroughly monitored and controlled.
It is essential to monitor chlorine levels in the distribution system to ensure that the proper level of chlorine residual is maintained to meet regulatory standards for disinfection, and to ensure that there is no excessive chlorine present.
In general, this optical method uses color intensity measurements to determine the concentration of chlorine in a solution. When appropriate buffer and indicator solutions are added to the sample, a reaction occurs producing a color, which intensity is proportional to the chlorine concentration. The color intensity is measured by eye, colorimeter or spectrophotometer. This method is susceptible to interference from color and turbidity in the sample, as well as some chemical substances besides chlorine, concurrently reacting with the indicator.
DPD method is the most widely used colorimetric method to measure chlorine. It can be used to measure both free and total chlorine with field, lab and online instrumentation. However, DPD method is subject to interference from other oxidants such as manganese, chromium and chloramines.
Indophenol method, being selective to monochloramine, can be used to measure monochloramine and free ammonia as well as free chlorine. Monochloramine is determined directly, while for determination of both monochloramine and free ammonia in the same sample method uses additional reagent to convert free ammonia into monochloramine. Free chlorine can also be measured by the indophenol method using a two-reagent system that is not subject to the interferences that affect the DPD method. However, this method is only available for the laboratory or field analyses and not for online analyzers.
This method determines chlorine concentration based on a completion of chemical reaction between the chlorine and titrant added to the sample. The titrant is added incrementally until the reaction is complete. The endpoint (or equivalence point) is the point at which the titrant and chlorine are balanced. The equivalence point can be determined visually using a color indicator or by using an electrochemical sensor. Manual, visual measurements are less precise and more susceptible to interference from color or turbidity in the sample, while titration using electrodes is more accurate and not susceptible to those interferences.
DPD-FEAS method uses a magenta visual indicator that is titrated to a colorless endpoint. This method measures free and total chlorine.
Iodometric method uses a blue visual indicator that disappears at the titration endpoint. This method is typically used to measure high concentrations of total chlorine.
This method represents amperometric titration to determine the endpoint either manually, or automatically. A small voltage is applied to the electrode and the endpoint is determined by a change in current, resulting from the reduction of chlorine by the titrant (phenylarsine oxide). The change in current and the volume of titrant are measured to correspond to the concentration of the chlorine. This method offers procedures for measuring both free and total chlorine, chlorine dioxide and chlorite, while using forward and back titration procedures.
This electrochemical method measures the change in electrical current resulting from chemical reactions taking place at the electrodes, with the current being proportional to the chlorine concentration. Different amperometric sensor designs are available, providing better selectivity for different chlorine species. This method is not susceptible to interference from color or turbidity in the sample, however, the sensor surface exposed to the sample is prone to fouling. Some amperometric analyzers do not require reagents. Amperometric sensors require maintenance and must be calibrated in-situ at a frequency dependent on the application.
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