83
Interferences
Summary of Method
Bromine reacts with DPD (N,N-diethyl-p-phenylenediamine) to
form a magenta color which is proportional to the total bromine
concentration.
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 separate sample aliquot, then add the same
amount to the sample being tested. Correct for volume
addition (See Section 1, Correcting for Volume
Additions).
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).
Chlorine 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 1 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 bromine concentration.
Monochloramine Interferes at all levels
Ozone Interferes at all levels
Peroxides May interfere
Extreme sample pH and
highly buffered samples
Adjust to pH 6-7. See Interferences, Section 1.
BROMINE, continued
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