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Chlorine, Free
5.
Remove the cell from
the adapter and add the
contents of one DPD Free
Chlorine powder pillow
to the sample. Cap and
shake the cell about 20
seconds to dissolve.
Interferences
Interfering Substance
Acidity
Alkalinity
Bromine, Br
2
Chlorine Dioxide, ClO
2
Chloramines, organic
Iodine, I
2
4+
Manganese, oxidized (Mn
7+
Mn
) or Chromium, oxidized
(Cr
6+
)
Monochloramine (NH
Cl)
2
Chlorine, Free
Page 2 of 4
6.
Place the prepared
sample into the adapter.
Greater than 150 mg/L CaCO
to pH 6–7 with1 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
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).
Interferes at all levels
Interferes at all levels
May interfere
Interferes at all levels
1. Adjust sample pH to 6–7 with 1.000 N Sulfuric Acid (Cat. No. 1270-32).
2. Add 2 drops Potassium Iodide (30 g/L) (Cat. No. 343-32) to a 5-mL sample.
,
3. Mix and wait 1 minute.
4. Add 2 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.
For conventional free chlorine disinfection (beyond the "breakpoint"), typical monochloramine
concentrations are very low. If monochloramine is present in the sample, its interference in the
free chlorine test is dependent on sample temperature, relative concentration of
monochloramine to free chlorine, and the time required to perform the analysis.
Typical interference levels of NH
NH
Cl Level
2
1.2 mg/L
2.5 mg/L
3.5 mg/L
5.0 mg/L
Read
7.
Touch
.
Read
Results will appear in
mg/L Cl
.
2
Interference Levels and Treatments
. May not develop full color or color may fade instantly. Neutralize
3
. May not develop full color or color may fade instantly. Neutralize
3
Cl (1 minute test time, interference as mg/L Cl
2
Sample Temperature ° C (° F)
5 (41)
10 (50)
+0.15
0.19
+0.35
0.38
+0.38
0.56
+0.68
0.75
):
2
20 (68)
30 (86)
0.30
0.29
0.55
0.61
0.69
0.73
0.93
1.05
ChlorineFre_MP_High_DPD_Eng_2400.fm
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