| 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
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.
