Hach DR2400 - Page 153

Chlorine Dioxide
Chlorine Dioxide
ChlorineDio_AVPP_Other_DPD_Eng_Ody.fm Page 3 of 6
Interferences
5. Add 16 drops of
Glycine Reagent to the
sample in the beaker.
Swirl gently to mix.
6. Fill a DPD Free
Chlorine Reagent
AccuVac Ampul with
sample. Keep the tip
immersed while the
ampule fills completely.
7. Quickly invert the
ampule several times to
mix. Wait 30 seconds for
any undissolved powder
to settle.
8. Within one minute of
adding the sample, wipe
the ampule and place it
into the cell holder.
Touch
Read.
Results will appear in
mg/L ClO
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).
Alkalinity
Greater than 250 mg/L CaCO
3
. Color may not develop fully or 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 the volume
addition (see Section 3.1.3 Correcting for Volume Additions).
Bromine, Br
2
Interferes at all levels.
Chlorine, Cl
2
May interfere at levels greater than 6 mg/L. Additional glycine may be able to compensate for this
interference.
Chloramines, organic May interfere.
Flocculating agents
High levels of most flocculating agents can be tolerated. This tolerance is decreased if chlorine is
present. See the information about metals in this table. In the presence of 0.6 mg/L Cl
2
, Al(SO
4
)
3
(< 500 mg/L) and FeCl
2
(<200 mg/L) may be tolerated.
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+
)
Oxidized manganese interferes at all levels. Oxidized chromium interferes at levels greater than
2 mg/L. To remove the interferences:
1. Adjust sample pH to 6–7.
2. Add 3 drops Potassium Iodide (30 g/L) (Cat. No. 343-32) to a 25-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.
Subtract the result of this test from the original analysis to obtain the correct chlorine dioxide
concentration.