Hach DR2400 - Page 148

Chlorine Dioxide
Chlorine Dioxide
Page 2 of 4
ChlorineDio_None_High_DRM_Eng_Ody.fm
Interferences
Sample Collection, Storage, and Preservation
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
Interfering Substance Interference Levels and Treatments
Acidity
Greater than 150 mg/L CaCO
3
. May not develop full color or color may fade instantly. Neutralize
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).
Alkalinity
Greater than 250 mg/L CaCO
3
. Color may not develop fully or may fade instantly. Neutralize to
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).
Bromine, Br
2
Interferes at all levels.
Chlorine, Cl
2
May interfere at levels greater than 6 mg/L. Additional glycine may be able to compensate for this
interference.
Chloramines, organic May interfere.
Flocculating agents
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
2
, Al(SO
4
)
3
(< 500 mg/L) and FeCl
2
(<200 mg/L) may be tolerated.
Hardness No effect at less than 1,000 mg/L as CaCO
3
.
Iodine, I
2
Interferes at all levels.
Manganese, oxidized
(Mn
4+
,Mn
7+
) or
Chromium, oxidized (Cr
6+
)
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.
* 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.
Metals
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
2
, both copper (>10 mg/L) and nickel (>50 mg/L) interfere. Other metals may also
interfere, depending on their ability to prevent glycine from reacting with any Cl
2
in the sample.
It may be necessary to add more glycine to overcome this interference.
Monochloramine
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
2
increase in the reading.
Ozone Interferes at levels greater than 1.5 mg/L.
Peroxides May interfere.
Extreme sample pH Adjust to pH 6–7. See Section 3.3 Interferences.
Highly buffered samples Adjust to pH 6–7. See Section 3.3 Interferences.