Quantitative determination of manganese ion | Autotitrator COM-A19 - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. G7 Apr. 5,2019
Metals Quantitative determination of manganese ion

1.Abstract

Manganese ion can be determined by chelatometric titration. The stability constant of Mn (II)-EDTA complex is relatively large (13.81),¹ but the suitable pH range for the reaction between manganese ion and EDTA is confined from 7 to 11. Since manganese ion is oxidized with air in alkaline solution, ascorbic acid or hydroxylamine is added for the titration to avoid the oxidation. The report introduces an example of the titration performed at alkaline condition (pH 10) adjusted by ammonia.

Mn²+ + Na₂EDTA  →  Mn-EDTA + 2Na+

2. Configuration of instruments and Reagents

(1) Configuration
  Main unit : Hiranuma Automatic Titrator COM series (Photometric titrator unit type M)
with 650 nm optical filter
  Electrode : Glass – Reference electrode GR-501BZ (for pH confirmation)
(2) Reagents    
  Titrant : 0.01 mol/L EDTA standard solution
  Buffer solution : 25 % ammonia solution
  Additive solution : Ascorbic acid
  Indicator : TPC indicator
Mix TPC (Thymolphthalein complexone) and potassium nitrate in
1:99 ratio [w/w] (hundredfold dilution).

3. Measurement procedure

(1) Dispense 20 mL of sample with volumetric pipette into a 100 mL beaker.
(2) Add about 60 mL of DI water.
(3) Add about 0.1 g of ascorbic acid.
(4) Add 3 ~4 drops of ammonia solution to adjust the pH to 10.
(5) Add about 0.1 g of TPC indicator.
(6) Immerse photometric probe into sample solution and titrate with 0.01 mol/L EDTA standard solution.

4. Measurement conditions and results

Examples of titration conditions

Quantitative determination of manganese ion Hiranuma Autotitrator COM-A19 from JM Science

Measurement results

Number of
measurement
Size
(mL)
Titrant
volume(mL)
Manganese ion
Concentration (ppm)
1 20 7.592 208.552
2 20 7.591 208.525
3 20 7.591 208.525
Statistic
calculation
Avg. 208.5 ppm
SD 0.0156 ppm
RSD 0.01 %

 

Examples of titration curves

5. Note

The following tips could help to improve the measurement accuracy. Manganese ion generates the precipitates of manganese hydroxide (Mn(OH)2) under alkaline condition. When performing titration at alkaline pH, the excess ammonium salt or the auxiliary complexing agent like tartrate salts or triethanolamine should be added before the titration. Regarding the interference by the coexistent ions, please note that a lot of metal ions interfere the titration at pH around 9 ~ 10.

Keywords: Manganese ion, Photometric titration, Chelatometric titration

References
(1) K. Ueno, “Chelatometry”, 1989, Nankodo, Tokyo.

*Some measurement would not be possible depending on optional configuration of system.

Hiranuma aquacounter autotitrator com-a19Metals

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