
150
CHLORINE DIOXIDE,
continued
Sampling and Storage
Analyze samples for chlorine dioxide
immediately
after
collection. Chlorine dioxide is a strong oxidizing agent, and it is
unstable in natural waters. It reacts rapidly with various inorganic
compounds and slowly oxidizes organic compounds. 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
demand.
Pretreat glass
sample containers to remove any
chlorine dioxide demand by soaking in a dilute bleach solution (1
mL commercial bleach to l liter of deionized water) for at least 1
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 introduced
when a representative sample is not obtained. 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 container 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 analysis immediately.
Note:
If the sample
temporarily turns yellow
after reagent addition, or the
display flashes “limit”, it is
due to high chlorine dioxide
levels. Dilute a fresh sample
with chlorine dioxide-free
water and repeat the test. A
slight loss of chlorine dioxide
may occur during dilution.
Multiply the result by the
dilution factor.
9.
Allow 30 seconds
for undissolved powder
to settle. Place the
AccuVac Ampul into the
cell holder. Tightly
cover the ampul with the
instrument cap.
10.
Press:
READ
The cursor will move to
the right, then the result
in mg/L chlorine dioxide
will be displayed.
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