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Reagent Preparation
Interferences
Interfering Substance
Alkalinity
Bromine, Br
2
Hardness
Iodine, I
2
4+
Manganese, oxidized (Mn
7+
Mn
) or Chromium, oxidized
6+
(Cr
)
Monochloramine (NH
Cl)
2
Ozone
* Samples treated with sodium arsenite for interferences will be hazardous waste as regulated by the Federal RCRA for arsenic
(D004). For information on pollution prevention and waste management, refer to Section 4. Refer to the instrument manual for
information on modifying the Pour-thru Cell for collecting sample after analysis.
Sampling and Storage
ChlorineFre_PT_Other_DPD_Eng_Ody.fm
The Free Chlorine Indicator Solution must be prepared before use. Using a
powder funnel, add the contents of one 24 g bottle of DPD Powder
(Cat. No. 22972-55) to one 473-mL bottle of Free Chlorine Indicator Solution
(Cat. No. 23140-11). Invert several times and swirl until the powder is
completely dissolved. A pink color may develop, but should not affect results.
This solution will give accurate results for at least one month after mixing when
stored at 20–25 °C (68–77 °C). Write the date of preparation on the Indicator
Solution Bottle. Discard any remaining solution after one month. Use of this
reagent after one month may result in high reagent blanks and low values at
high concentration. Do not combine fresh reagent with previously
mixed reagent.
Greater than 400 mg/L CaCO
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 volume addition
(see Section 3.1.3 Correcting for Volume Additions on page 29).
Interferes at all levels.
Levels below 1000 mg/L as CaCO
Interferes at all levels.
1. Adjust sample pH to 6–7 with 1.000 N Sulfuric Acid (Cat. No. 1270-32).
2. Add 9 drops Potassium Iodide (30 g/L) (Cat. No. 343-32) to a 80-mL sample.
,
3. Mix and wait 1 minute.
4. Add 9 drops Sodium Arsenite* (5 g/L) (Cat. No. 1047-32) and mix.
5. Analyze the treated sample as described in the procedure above.
6. Subtract the result of this test from the original analysis to obtain the correct concentration.
Samples containing monochloramine will cause a gradual drift to higher chlorine readings. When
read within one minute of reagent addition, 3.0 mg/L monochloramine will cause an increase of
less than 0.1 mg/L in the free chlorine reading.
Interferes at all levels.
Samples must be analyzed immediately and cannot be preserved for later
analysis. A common testing error is introduced if the analyst does not obtain a
representative sample. If sampling from a tap, let the water flow for at least five
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. Perform the chlorine analysis immediately.
Avoid plastic containers since these may have a chlorine demand. Pre-treat glass
sample containers to remove any chlorine 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 water.
Interference Levels and Treatments
. May not develop full color or color may fade instantly. Neutralize
3
will not interfere.
3
Chlorine, Free
Chlorine, Free
Page 3 of 6
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