Determination of alkalinity in bottled water | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. D5 Nov. 14,2018
Environment Determination of alkalinity in bottled water

1. Abstract

 Natural water contains alkaline components such as hydroxides and carbonates. Such water indicates alkaline 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 (P alkalinity) and total alkalinity (T alkalinity or M alkalinity) by the pH value of neutralization point.

Alkalinity P Alkalinity ……………Endpoint at pH 8.3
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.

2OH⁻ + H₂SO₄ → SO₄²⁻ + 2H₂O  
2CO₃²⁻ + H₂SO₄ → SO₄²⁻ + 2HCO₃⁻  

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

HCO₃⁻ + H₂SO₄ → SO₄²⁻ + 2CO₂ + H₂O  

 This 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 electrode GE-101B
Reference electrode RE-201Z
Thermistor electrode TE-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

Examples of titration conditions

(1) Titration of P alkalinity

Determination of alkalinity in bottled water

(2) Titration of T (M) alkalinity

Determination of alkalinity in bottled water

Measurement results

Results of P Alkalinity
Number of
measurement
Size
(mL)
Titrant
volume(mL)
Concentration
(CaCO₃ mg/L)
1 100 1.024 10.281
2 100 1.017 10.211
3 100 1.034 10.381
Statistic
calculation
Avg. 10.2 mg/L
SD 0.0854 mg/L
RSD 0.83 %

 

Results of T (M) Alkalinity
Number of
measurement
Size
(mL)
Titrant
volume(mL)
Concentration
(CaCO₃ mg/L)
1 100 5.117 61.656
2 100 5.120 61.615
3 100 5.108 61.666
Statistic
calculation
Avg. 61.6 mg/L
SD 0.0270 mg/L
RSD 0.04 %

 

Examples of titration curves

5. Note

 The 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 as endpoint, 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.

EnvironmentHiranuma aquacounter autotitrator com-a19

Featured Instruments

Aquacounter Potentiometric Titrator COM-A19 | HiranumaAquacounter Potentiometric Titrator COM-A19 | Hiranuma
Hiranuma Aquacounter Potentiometric Titrator COM-A19 | Hiranuma
Sale price$11,490.00 USD Regular price$12,490.00 USD

Featured Titrators

View all
Aquacounter AQ-300 Coulometric Karl Fischer Titrator | Hiranuma
Hiranuma Aquacounter AQ-300 Coulometric Karl Fischer Titrator | Hiranuma
Sale price$5,800.00 USD Regular price$6,990.00 USD
Aquacounter Volumetric Karl Fischer Titrator MOIVO-A19 | Hiranuma
Hiranuma Aquacounter Volumetric Karl Fischer Titrator MOIVO-A19 | Hiranuma
Sale price$11,990.00 USD Regular price$13,990.00 USD
Aquacounter Coulometric Karl Fischer Titrator MOICO-A19 | Hiranuma
Hiranuma Aquacounter Coulometric Karl Fischer Titrator MOICO-A19 | Hiranuma
Sale price$10,990.00 USD Regular price$12,490.00 USD
Aquacounter Potentiometric Titrator COM-A19 | HiranumaAquacounter Potentiometric Titrator COM-A19 | Hiranuma
Hiranuma Aquacounter Potentiometric Titrator COM-A19 | Hiranuma
Sale price$11,490.00 USD Regular price$12,490.00 USD
Aquacounter AQV-300 Volumetric Karl Fischer Titrator | Hiranuma - JM Science
Hiranuma Aquacounter AQV-300 Volumetric Karl Fischer Titrator | Hiranuma
Sale price$5,800.00 USD Regular price$6,990.00 USD
Aquacounter COM-300A Potentiometric Titrator | Hiranuma - JM Science
Hiranuma Aquacounter COM-300A Potentiometric Titrator | Hiranuma
Sale price$6,490.00 USD Regular price$6,990.00 USD