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Chlorine Dioxide
Interfering Substance
Metals
Monochloramine
Ozone
Peroxides
Extreme sample pH
Highly buffered samples
* Samples treated with sodium arsenite for interferences will be hazardous waste as regulated by Federal RCRA for arsenic
(D004). See Section 4 for further information on proper disposal of these materials.
Sample Collection, Storage, and Preservation
Accuracy Check
Chlorine Dioxide
Page 4 of 6
Various metals may interfere by combining with the glycine needed to remove the chlorine
interference. Metal interference is limited except when chlorine is present. In the presence of
0.6 mg/L Cl
, both copper (>10 mg/L) and nickel (>50 mg/L) interfere. Other metals may also
2
interfere, depending on their ability to prevent glycine from reacting with any Cl
It may be necessary to add more glycine to overcome this interference.
Causes a gradual drift to higher readings. When read within 1 minute after reagent addition,
3 mg/L monochloramine causes less than a 0.1 mg/L ClO
Interferes at levels greater than 1.5 mg/L.
May interfere.
Adjust to pH 6–7. See Section 3.3 Interferences.
Adjust to pH 6–7. See Section 3.3 Interferences.
Analyze samples for chlorine dioxide immediately after collection. Chlorine
dioxide is a strong oxidizing agent and is unstable in natural waters. It reacts
rapidly with various inorganic compounds, but oxidizes organic compounds
more slowly. Many factors, including reactant concentrations, sunlight, pH,
temperature, and salinity influence decomposition of chlorine dioxide in water.
Avoid plastic containers since these may have a large chlorine dioxide demand.
Pretreat glass sample containers to remove any chlorine or chlorine dioxide
demand by soaking in a dilute bleach solution (1 mL commercial bleach to l liter
of deionized water) for at least one hour. Rinse thoroughly with deionized or
distilled water. If sample containers are rinsed thoroughly with deionized or
distilled water after use, only occasional pretreatment is necessary.
A common error in testing for chlorine dioxide is not obtaining a representative
sample. If sampling from a tap, let the water flow for at least 5 minutes to ensure
a representative sample. Let the container overflow with the sample several
times, then cap the sample containers so there is no headspace (air) above the
sample. If sampling with a sample cell, rinse the cell several times with the
sample, then carefully fill to the 10-mL mark. Perform the chlorine dioxide
analysis immediately.
Because chlorine dioxide is difficult and hazardous to produce, check the DPD
and glycine reagents by using chlorine standards. Proceed as follows:
1. Prepare a 1-mg/L free chlorine standard using Method 1 or 2, below:
Method 1
a. Use Free Chlorine Standard (Cat. No. 14268-10).
b. Determine the concentration of the standard from the certificate of
analysis shipped with the standard (50–75 mg/L). Calculate the volume
of standard needed as follows:
mL standard needed = 100
Interference Levels and Treatments
÷
standard concentration
in the sample.
2
increase in the reading.
2
ChlorineDio_AVPP_Other_DPD_Eng_Ody.fm
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