Hach DR/850 Procedures Manual page 123

CHLORINE, FREE
Interferences
Interfering Substance
Acidity
Alkalinity
Bromine
Chlorine Dioxide
Chloramines, organic
Hardness
Iodine
Manganese, Oxidized
4+ 7+
(Mn , Mn )
or
Chromium , Oxidized (Cr
Monochloramine
Ozone
Peroxides
Extreme sample pH and highly
buffered samples
Summary of Method
continued
Greater than 150 mg/L CaCO
instantly. Neutralize to pH 6-7 with 1 N sodium hydroxide. 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 1, Correct-
ing for Volume Additions).
Greater than 250 mg/L CaCO
instantly. Neutralize to pH 6-7 with 1 N sulfuric acid. 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 1, Correcting for Volume Additions).
Interferes at all levels
Interferes at all levels
May interfere
No effect at less than 1,000 mg/L as CaCO
Interferes at all levels
1. Adjust sample pH to 6-7.
2. Add 3 drops potassium iodide (30 g/L) to a 25-mL sample.
3. Mix and wait one minute.
6+
) 4. Add 3 drops sodium arsenite (5 g/L) and mix.
5. Analyze 10 mL of the treated sample as described in the procedure.
6. Subtract the result from this test from the original analysis to obtain the cor-
rect chlorine concentration.
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 increase
in the reading.
Interferes at all levels
May interfere
Adjust to pH 6-7. See Interferences, Section 1.
Chlorine in the sample as hypochlorous acid or hypochlorite ion
(free chlorine or free available chlorine) immediately reacts with
DPD (N,N-diethyl-p-phenylenediamine) indicator to form a
magenta color which is proportional to the chlorine
concentration.
Interference Level and Treatment
. May not develop full color or color may fade
3
. May not develop full color or color may fade
3
3
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