Chlorine, Free
Chlorine, Free
ChlorineFre_AVPP_Other_DPD_Eng_Ody.fm Page 3 of 6
Interferences
5. Fill a DPD Free
Chlorine Reagent
AccuVac Ampul with
sample. Keep the tip
immersed while the
ampule fills completely.
6. Quickly invert the
ampule several times to
mix. Wipe off any liquid
or fingerprints.
7. Within one minute of
sample addition, wipe
the AccuVac Ampul and
place it into the cell
holder.
8. Touch Read.
Results will appear in
mg/L Cl
2
.
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 on page 29).
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 (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).
Bromine, Br
2
Interferes at all levels
Chlorine Dioxide, ClO
2
Interferes at all levels
Chloramines, organic May interfere
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+
)
1. Adjust sample pH to 6–7.
2. Add 3 drops Potassium Iodide (30-g/L) (Cat. No. 343-32) to a 10-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.
6. Subtract the result from this test from the original analysis to obtain the correct chlorine
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.
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 increase in the reading.
Ozone Interferes at all levels
Peroxides May interfere
Extreme sample pH or Highly
buffered samples
Adjust to pH 6–7 using acid (Sulfuric Acid, 1.000 N, Cat. No. 1270-32) or base (Sodium
Hydroxide, 1.00 N, Cat. No. 1045-32).
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