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Chlorine Dioxide
Interferences
Interfering Substance
Acidity
Alkalinity
Bromine, Br
2
Chlorine, Cl
2
Chloramines, organic
Flocculating agents
Hardness
Iodine, I
2
Manganese, oxidized
(Mn
4+
, Mn
7+
) or
Chromium, oxidized (Cr
6+
)
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
Chlorine Dioxide
Page 2 of 4
Greater than 150 mg/L CaCO
to pH 6–7 with 1 N Sodium Hydroxide (Cat. No. 1045-32). Determine amount to be added on
separate sample aliquot, then add the same amount to the sample being tested. Correct for volume
addition (see Section 3.1.3 Correcting for Volume Additions).
Greater than 250 mg/L CaCO
pH 6–7 with 1 N Sulfuric Acid (Cat. No. 1270-32). Determine amount to be added on separate
sample aliquot, then add the same amount to the sample being tested. Correct for the volume
addition (see Section 3.1.3 Correcting for Volume Additions).
Interferes at all levels.
May interfere at levels greater than 6 mg/L. Additional glycine may be able to compensate for this
interference.
May interfere.
High levels of most flocculating agents can be tolerated. This tolerance is decreased if chlorine is
present. See the information about metals in this table. In the presence of 0.6 mg/L Cl
(< 500 mg/L) and FeCl
(<200 mg/L) may be tolerated.
2
No effect at less than 1,000 mg/L as CaCO
Interferes at all levels.
Oxidized manganese interferes at all levels. Oxidized chromium interferes at levels greater than
2 mg/L. To remove the interferences:
1. Adjust sample pH to 6–7.
2. Add 3 drops Potassium Iodide (30 g/L) (Cat. No. 343-32) to a 25-mL sample.
3. Mix and wait one minute.
4. Add 3 drops Sodium Arsenite* (5 g/L) (Cat. No. 1047-32) and mix.
5. Analyze 10 mL of the treated sample as described in the procedure.
Subtract the result of this test from the original analysis to obtain the correct chlorine dioxide
concentration.
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
Interference Levels and Treatments
. May not develop full color or color may fade instantly. Neutralize
3
. Color may not develop fully or may fade instantly. Neutralize to
3
.
3
, Al(SO
2
in the sample.
2
increase in the reading.
2
ChlorineDio_None_High_DRM_Eng_Ody.fm
)
4
3
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