HIRANUMA APPLICATION DATA

Data No.

Automatic Titrator

D5Nov. 14,
2018

Determination of alkalinity inbottled water

Environment

1. Abstract
Natural water contains alkaline components such as hydroxides and carbonates. Such water indicatesalkaline pH, the alkalinity is used as an index. The alkalinity is expressed as mg/L of calcium carbonate(CaCO3) equivalent for these alkaline components. Alkalinity is divided into phenolphthalein alkalinity (Palkalinity) and total alkalinity (T alkalinity or M alkalinity) by the pH value of neutralization point.
P Alkalinity ………….Endpoint at pH 8.3
Alkalinity
T (M) Alkalinity ……...Endpoint at pH 4.8
Total amount of the hydroxides and half amount of carbonates are measured when it is titrated to about
pH 8.3 with sulfuric acid titrant.
2OH2CO32-++

H2SO4→

SO42-+2H2O

H2SO4→

SO42-+

2HCO3-All of the bicarbonates are neutralized when it is titrated successively to about pH 4.8.
HCO3-+

H2SO4→

SO42-+

2CO2+H2OThis report introduces a measurement example for bottled water using potentiometric titration as end
point detection method according to Standard Methods for the Examination of Water.

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

Hiranuma Automatic Titrator COM series

Electrodes:

Glass electrodeGE-101B

Reference electrodeRE-201Z

Thermistor electrodeTE-403*Instead of above electrode, the following electrodes are usable.
・Glass reference combination electrode GR-501B…Fixed sleeve type・Glass reference combination electrode GR-511B…Moveable sleeve type(2) Reagents
Titrant: 0.01 mol/L Sulfuric acid standard solution

3. Measurement procedure(1) Dispense 100 mL of sample into a 200 mL beaker with volumetric pipette.
(2) Immerse electrodes and start titration with 0.01 mol/L sulfuric acid standard solution.

4. Measurement conditions and results
Example of titration condition(1) Titration of P alkalinity
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mL
Direction
T Timer
D.P. mL
Endpoint pH
Over mL
Max.Vol.

1Set

11pH
50↓
00
8.3
05sec
mL
sec
mL
mL
mL

ConstantNo.
SizeBlank
Molarity
FactorKLUnit
Formula1
10000.01
1.004100.00
0.000mLmL
mol/L

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt SpeedPulse

505033240

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt SpeedPulse

505033240sec
mV
sec
mV

PPM

DigitsAuto In Pram.

(D-B)*K*F*M*1000/S
3Non

ConstantNo.
Size
Blank
Molarity
Factor
KL

2100
00.01
1.004
100.000(2) Titration of T (M) alkalinity
Cndt No.
MethodBuret No.
Amp No.
D. Unit
S-Timer
C.P. mL
Direction
T Timer
D.P. mL
Endpoint pHOver mL
Max.Vol.

2Set

11pH00↓
00
4.8
0.2
10sec
mL
secmL
mL
mL

Unit
FormulaDigits
Auto In Pram.

mL
mL
mol/L

PPM(VA+VB)*K*F*M*1000/S
3Non*Some measurement would not be possible depending on optional configuration of system.

secmV
sec
mV

Measurement results
Results of P Alkalinity
Number ofSize

Titrant

Concentration

Measurement(mL)

Volume (mL)

(CaCO3 mg/L)

1100

1.024

10.281

2100

1.017

10.211

3100

1.034

10.381

Statisticcalculation

Avg.

10.2 mg/L

SD

0.0854 mg/L

RSD

0.83 %

Results of T (M) Alkalinity

Example of titration curve

Number ofSize

Titrant

Concentration

Measurement(mL)

Volume (mL)

(CaCO3 mg/L)

1100

5.117

61.656

2100

5.120

61.615

3100

5.108

61.666

Statistic
calculation

Avg.

61.6 mg/L

SD

0.0270 mg/L

RSD

0.04 %

5. NoteThe alkalinity is accurately determined by potentiometric titration instead of color indicator titration.
Owing to function of conditions connection, the successive titration of P alkalinity and T (M) alkalinity
can be efficiently performed.
Setting for endpoint detection is “Set” method on this titration. Since the specified pH is detected asendpoint, the exact pH detection is required. Therefore pH calibration with pH standard solutions is necessary
before the measurement.
Keywords: Bottled water, Alkalinity, P alkalinity, T (M) alkalinity, Standard Methods for the Examination of Water*Some measurement would not be possible depending on optional configuration of system.