The analysis of chlorine dioxide and chlorite in water can sometimes be difficult as chlorine dioxide is a volatile molecule, and standard test methods for measuring chlorine dioxide and chlorite can suffer interferences from other species.
There are a variety of methods available for testing chlorine dioxide and chlorite in water. Many are laboratory based, however there portable colorimetric and electrochemical methods are also available.
Ion chromatography is a laboratory-based method which works by separating out ions in solution. This method is used for measuring both chlorine dioxide and chlorite, and it is the standard method for measuring chlorite (4110 Determination of Oxyhalides using Ion Chromatography).
Colorimetric methods include DPD and Lissamine Green. Traditionally, the most used colorimetric method for testing chlorine dioxide was the DPD method. This method has been removed as a standard method due to concerns over chlorite interference, however it is still an EPA approved method. Lissamine Green is another indicator used to measure chlorine dioxide and chlorite. This is not a standard method, but it is an EPA approved method for measuring chlorine dioxide.
Amperometric methods are also used. Standard method 4500–ClO2 C and 4500–ClO2 E are both amperometric methods used for the measurement of ClO2 in water. Both methods are electrochemical methods which work by measuring current flow when a fixed voltage is applied to the electrode. This is the method Kemio Disinfection is based on.
More information on these and other standard methods for measuring chlorine dioxide and chlorite can be found in APHA AWWA WEF Standard Methods for the Examination of Water and Wastewater.
The US EPA require that both chlorine dioxide (ClO2) and chlorite (ClO2–) are monitored daily at the start of a distribution network. They also specify that chlorite is measured less frequently at various points throughout a network.
The following are methods that have been approved by the USEPA for chlorine dioxide monitoring:
DPD has been removed as a standard method for determining ClO2 by the AWWA Standard Methods committee.
Ion chromatography is one of the main methods approved for chlorite monitoring. This method is not as portable as Kemio Disinfection, making Kemio Disinfection the only truly portable USEPA approved method for determining chlorite.
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