HIRANUMA APPLICATION DATA

Data No.

Automatic Titrator

D4

Nov. 14,2018

Determination of residual chlorine
in tap water

Environment

1. Abstract
Tap water chlorinated from lake water and river water contains residual chlorine. The residual chlorine issometimes called available chlorine, which is composed of free residual chlorine and combined residualchlorine.
Free residual chlorine (Cl2, HClO, ClO-)
Residual chlorine
Combined residual chlorine (NH2Cl, NHCl2, NHCl3, …Chloramine)(Available chlorine)Standard Methods for the Examination of Water adopts the following methods as determination method
for residual chlorine.
・Dimethyl -p- phenylenediamine (DPD) method…….….……………………………Colorimetric method
・Dimethyl -p- phenylenediamine (DPD) titration method……………………………Titration method
・Amperometric titration method (Titration method with phenylarsenoxide solution)…Titration method・Iodometric titration method …..…….….………….….……………………………….Titration method
This report introduces an example for determination of residual chlorine in tap water with iodometrictitration method. Residual chlorine oxidizes potassium iodide in acidic solution to generate free iodine.

Cl2+2I-→

I2+2Cl-The generate iodine is potentiometrically titrated with sodium thiosulfate standard solution.

I2+2Na2S2O3→

2NaI+Na2S4O6

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit:

Hiranuma Automatic Titrator COM series

Electrode:

Platinum electrodePT-301

Reference electrodeRE-201Z*Instead of above electrodes, the following electrodes are useable.
・PR-701BZ (Platinum reference combination electrode)・ Combination of PT-301 (Platinum Electrode) and GR-501BZ (Glassreference electrode)(2) Reagents
Titrant: 0.01 mol/L Sodium thiosulfate standard solution

Additive solution: Diluted sulfuric acid (1:5, v/v)

Additive reagent: Potassium iodide

3. Measurement procedure(1) Dispense 500 mL of sample into a 500 mL beaker with graduated cylinder.
(2) Add 1 g of potassium iodide and 5 mL of diluted sulfuric acid.
(3) Immerse electrodes and start titration with 0.01 mol/L sodium thiosulfate standard solution.

4. Measurement conditions and results
Example of titration condition
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mLT Timer
D.P. mLEnd Sens
Over mL
Max.Vol.

1Auto

12mV
100003000.120sec
mL
sec
mL
mLmL

ConstantNo.
SizeBlank
Molarity
FactorKL

1500
00.010
1.007
35.45
0Unit
FormulaDigits
Auto In Pram.

PPM(D-B)*K*F*M*1000/S
3NonmLmLmol/L

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

500053216sec
mV
sec
mV

Measurement results
Number ofSize

Titrant

Concentration

Measurement(mL)

Volume (mL)

(mg/L)

1500

0.772

0.551

2500

0.773

0.552

3500

0.755

0.539

4500

0.771

0.550

5500

0.772

0.551

Statistic
calculation

Avg.

0.549 mg/L

SD

0.0054 mg/L

RSD

0.98 %

Example of titration curve

5. NotePotentiometric titration with platinum electrode is introduced in this report instead of using starchsolution as indicator for endpoint detection. While the detection method with starch indicator is likely to cause
individual error due to visual judgment, the potentiometric titration automatically detects the maximum change
point in potential, can perform measurement with less individual error. Determination limit is estimated toabout 0.1 mg/L.
Please note that the sum of free residual chlorine and combined residual chlorine is determined on thismethod. When performing separated titration, the measurement with DPD method or amperometric titration
method are required.
Keywords: Tap water, Residual chlorine, Standard Methods for the Examination of Water, Platinum electrode*Some measurement would not be possible depending on optional configuration of system.