| HIRANUMA APPLICATION DATA | Automatic Titrator | Data No. | N2 | Feb. 10,2021 |
| Cement Concrete | Determination of chloride ion in concrete |
1. Abstract
This report introduces an example of the determination of chloride ion in concrete.
This measurement method is described in “Potentiometric titration method using chloride ion-selective electrode” of “JIS A 1154 Method of test for chloride ion content in hardened concrete”. Nitric acid is added to adjust the pH to 3 or less, and extract chloride ion with boiling. Cool to room temperature, filtrate to separate undissolved component and collect filtrated solution as sample. Chloride ion is determined by precipitation titration using a silver nitrate standard solution.
| Cl⁻ ＋ AgNO₃ → AgCl ＋ NO₃⁻ |
2. Configuration of instruments and Reagents
| (1) | Configuration | ||
| Main unit | : | Automatic Titrator COM series | |
| Electrode | : | Chloride ion-selective electrode CLi-081 (Connect to IE-2) Reference electrode MS-231Z (Connect to RE-2) *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 MS-231Z use mercury (I) sulfate. When these electrodes are disposed, please ask the specialized industrial waste disposal operator. |
|
| Filter paper | : | For quantitative analysis | |
| (2) | Reagents | ||
| Titrant | : | 0.005 mol/L Silver nitrate standard solution | |
| Additive | : | Diluted nitric acid Prepared by mixing nitric acid (60 %) in a volume ratio of 1 to 6 in DI water |
|
3. Measurement procedure
| (1) | Take 10 g of sample into a 200 mL beaker and accurately weigh it. |
| (2) | Add 70 mL of diluted nitric acid slowly and stirrer it. Then measure the pH to confirm the pH is 3 or less. |
| (3) | Cover the beaker with watch glass and heat to boil for 5 minute. Then cool it to room temperature. |
| (4) | Filtrate the solution using filter paper with aspirating and wash the filter paper with water. |
| (5) | Collect filtrated solution into a volumetric flask to make it 200 mL with DI water. |
| (6) | Take the solution prepared at (5) with a 50 mL volumetric pipet into a 100 mL beaker. |
| (7) | Immerse electrodes and titrate with 0.005 mol/L silver nitrate standard solution. |
4. Measurement conditions and results
Examples of titration conditions
| Cndt No. | 1 | |
| Method | Auto | |
| Buret No. | 1 | |
| Amp No. | 2 | |
| D. Unit | mV | |
| S-Timer | 5 | sec |
| C.P. mL | 0 | mL |
| T Timer | 0 | sec |
| D.P. mL | 0.1 | mL |
| End Sens | 30 | |
| Over mL | 0.5 | mL |
| Max Vol. | 20 | mL |
| Constant No. | 1 | |
| Size | 10.0314 | g |
| Blank | 0 | mL |
| Molarity | 0.005 | mol/L |
| Factor | 1 | |
| K | 35.45 | |
| L | 50 | |
| Unit | % | |
| Formula | ||
| (D-B)*K*F*M/(S*10)*200/L | ||
| Decimal Places | 4 | |
| Mode No. | 8 | |
| Pre Int | 0 | sec |
| Del K | 5 | |
| Del Sens | 0 | mV |
| Int Time | 5 | sec |
| Int Sens | 3 | mV |
| Brt Speed | 2 | |
| Pulse | 40 | |
Measurement results
| Number of measurement |
Sample size(g) |
Titration volume(mL) |
Chloride ion (%) |
|---|---|---|---|
| 1 | 2.326 | 0.0164 | |
| 2 | 10.0314 | 2.340 | 0.0165 |
| 3 | 2.296 | 0.0162 | |
| Avg. | 0.0164 % | ||
| SD | 0.0002 % | ||
| RSD | 0.93 % |
Example of titration curve
5.Note
・Indicator electrode
Chloride ion-selective electrode was used as an indicator electrode for this measurement.
In addition to the above electrode, a silver electrode coated with silver chloride (model: AG-311A) can also be used for this measurement. However, since the silver electrode coated with silver chloride deteriorates after long-term use, the electrode potential change near the end point becomes small and unclear. On the other hand, the chloride ion-selective electrode has the advantage that when the sensitivity deteriorates, the sensitivity can be easily restored by lightly polishing the sensitive membrane with a sandpaper.
Keywords： Chloride ion, Precipitation titration, Concrete, JIS A1154
*Some measurement would not be possible depending on optional configuration of system.
