| HIRANUMA APPLICATION DATA | Automatic Titrator | Data No. | A1 | Apr.19,2018 |
| FOOD | Salt content in soy sauce |
1. Abstract
The determination method of salt content in soy sauce is described as “Measurement of Salt Content” in JAS (Japanese Agriculture Standard). Potentiometric titration and Mohr method is defined in JAS as determination method of salt content, potentiometric titration is more common method because of its ease and high precision. The sample is acidified by nitric acid and the concentration of salt is determined by precipitation titration with silver nitrate titrant using the silver electrode.
NaCl ＋ AgNO₃ → AgCl ＋ NaNO₃
2. Configuration of instruments and reagents
| (1) | Instruments | ||
| Main unit | : | Hiranuma Automatic Titrator COM Series | |
| Electrode | : | Silver combination electrode AGR-811Z (Double Junction Type) *The following electrodes are also usable. ・AGR-801Z (Silver reference combination electrode) ・Combination of AG-311 (Silver indicator electrode) and MS-231Z (Silver reference electrode) ・Combination of AG-311 and RE-241Z (Double junction type silver reference electrode) *Remark The general reference electrode (RE-201Z) cannot be used for this titration because KCl inner solution might come out to sample solution and it causes measurement error. The inner electrodes of AGR-801Z and MS-231Z use mercury (I) sulfate. When these electrodes are disposed, please ask the specialized industrial waste disposal operator. |
|
| (2) | Reagents | ||
| Titrant | : | 0.1 mol/L Silver nitrate standard solution | |
| Additive | : | Diluted nitric acid (1:1, v/v) 1 mL |
3. Measurement procedure
| (1) | Take 5 ml of sample by volumetric pipette accurately and dilute it to 250 ml with volumetric flask. |
| (2) | Take 10 ml of above sample into a 100 ml beaker. |
| (3) | Add 50 ml of DI water. |
| (4) | Add 1 ml of diluted nitric acid. |
| (5) | Immerse the electrodes and titrate with 0.1 mol/L standard silver nitrate solution. |
4. Measurement conditions and results
Examples of titration conditions
Example of titration curve
Measurement results
|
Number of measurement |
Size (mL) |
Titrant volume (mL) |
Salt concentration (%) |
|---|---|---|---|
|
1 |
|
5.653 |
16.584 |
|
2 |
0.2 ※ |
5.652 |
16.581 |
|
3 |
|
5.656 |
16.593 |
|
|
|
Avg. |
16.59% |
|
|
|
SD |
0.006% |
|
|
|
RSD |
0.04% |
*Actual sample volume will be 0.2 mL (10／50) because 10 ml of 50-fold diluted sample is used.
5.Note
“Int time” should be set to longer than usual, because the generating speed of silver chloride would get slower near the end point and the lower temperature would decrease the response speed. It would improve the measurement accuracy.
Keywords： Soy source, Salt content, Precipitation titration, Silver electrode, Silver nitrate
*Some measurement would not be possible depending on optional configuration of system.
