Hach DR/850 - Page 136

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Method Performance
Precision
In a single laboratory using a standard solution of 2.53 mg/L
chlorine and two representative lots of reagents with the
instrument, a single operator obtained a standard deviation of
±0.14 mg/L chlorine.
Estimated Detection Limit (EDL)
The estimated detection limit for program 10 is 0.03 mg/L Cl
2
.
For more information on derivation and use of Hach’s estimated
detection limit, see Section 1.
Interferences
Interfering Substance Interference Level and Treatment
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. Determine amount to be added on sep-
arate sample aliquot, then add the same amount to the sample being tested. Correct for
volume addition (See Section 1, Correcting for Volume Additions in the DR/800 Series
Procedures Manual).
Alkalinity Greater than 250 mg/L CaCO
3
. May not develop full color or color may fade 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).
Bromine Interferes at all levels
Chlorine Dioxide Interferes at all levels
Chloramines, organic May interfere
Hardness No effect at less than 1,000 mg/L as CaCO
3
Iodine Interferes at all levels
Manganese, oxidized
(Mn
4+
, Mn
7+
)
or
Chromium , oxidized
(Cr
6+
)
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.
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 correct
chlorine concentration.
CHLORINE, FREE continued