LaMotte DPD-FAS TITRIMETRIC OUT FIT DT - Manual (Page 3)

PROCEDURES
I. DPD METHOD FOR FREE & COMBINED CHLORINE
A. FREE CHLORINE
1.
Use the 0.5 g spoon (0698) to add 0.5 g of *DPD #1 Powder (6807)
to the 250 mL Erlenmeyer flask (0433).
2. Fill the 100 mL graduated cylinder (0419) to the 100 mL line with
sample water. Pour into Erlenmeyer flask. Swirl until powder is
dissolved. If free chlorine is present, solution will turn pink.
NOTE:
In the presence of high monochloramine, add 10 drops of
*Steadifac Reagent (6383WT) to prevent interference. This will
give a Free Chlorine reading only. Discard and start again at Step
1A and continue to Step B5 for monochloramine, etc. Do not add
*Steadifac Reagent if other forms of chlorine are to be determined.
3. Titrate rapidly with the diluted Ferrous Ammonium Sulfate Solution
in the buret until the pink color disappears. Record buret reading as
Reading A.
Reading A (mL) = (ppm) Free Chlorine
Retain sample and buret for testing Monochloramine.
B. MONOCHLORAMINE
4.
Use the 1.0 g spoon (0697) to add one small *Potassium Iodide
Crystal (6809) to the sample from Step 3. Swirl to mix. If
monochloramine is present, solution will turn pink.
NOTE:
If dichloramine concentration is expected to be high,
substitute 2 drops Potassium Iodide, 0.5% (6810) for one *Potassium
Iodide Crystal (6809) in Step 4.
5. Continue titrating with the diluted Ferrous Ammonium Sulfate
Solution until the pink color disappears. Record buret reading as
Reading B.
(Reading B – Reading A), mL = (ppm) Monochloramine
Retain sample and buret for testing Dichloramine.
C. DICHLORAMINE
6.
Use the 1.0 g spoon (0697) to add 1.0 g of *Potassium Iodide
Crystals (6809) to the sample from Step 5. Swirl until crystals are
dissolved. Wait 2 minutes. If Dichloramine is present, solution will
turn pink.
7. Continue titrating with the diluted Ferrous Ammonium Sulfate
Solution until the pink color disappears. Record buret reading as
Reading C.
Reading C (mL) = (ppm) Total Chlorine
(Reading C – Reading B), mL = (ppm) Dichloramine3
3