Hach POCKET COLORIMETER II, Instruction Manuals

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1—61
Chlorine Dioxide,
continued
Sampling and Storage
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.
Do not use plastic containers to collect samples for analysis since they often have a
high 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 each use, only occasional pretreatment is necessary thereafter.
Failure to obtain a representative sample is a common error in testing for chlorine
dioxide. 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.
Accuracy Check