HJ 962-2018Soil - Determination of pH - Potentiometry (English PDF)

Foreword

To implement the "Environmental Protection Law of the People's Republic of China", protect the ecological environment, protect human health, and regulate soil pH the method of determination is to develop this standard.

This standard specifies the potential method for determining soil pH.

Appendix A of this standard is an informative annex.

This standard is the first release.

This standard is formulated by the Environmental Monitoring Department and the Science and Technology Standards Department.

This standard was drafted. Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Jiangsu Environmental Monitoring Center.

This standard is verified by. Hunan Environmental Monitoring Center Station, Suzhou Environmental Monitoring Center, Jiangsu Kangda Testing Technology Unit Co., Ltd., Su Li Environmental Technology Co., Ltd., Jiangsu Geological Survey Research Institute and Shanghai Real Testing Technology Service Limited.

This standard is approved by the Ministry of Ecology and Environment on July 29, 2018.

This standard has been implemented since January 1, 2019.

This standard is explained by the Ministry of Ecology and Environment.

1 Soil pH determination potential method

1 Scope of application this standard specifies the potential method for determining soil pH.

This standard applies to the determination of soil pH.

2 Normative references

This standard refers to the following documents or their terms. For undated references, the valid version applies to this standard.

HJ/T 166 Technical Specifications for Soil Environmental Monitoring

3 Principle of the method

Using water as the extractant, the water-soil ratio is 2.5.1, and the indicator electrode and the reference electrode (or pH composite electrode) are immersed in the soil suspension.

In the case of turbid liquid, a primary battery is formed. At a certain temperature, the electromotive force is related to the pH value of the suspension, and the original electricity is measured.

The electromotive force of the pool gives the pH of the soil.

4 Reagents and materials

Unless otherwise stated, analytically pure reagents that meet national standards were used for the analysis.

4.1 Experimental water. freshly prepared distilled water or pure water from which carbon dioxide is removed.

Water was poured into the flask, boiled for 10 min, and allowed to cool. Use the current system.

4.2 Potassium hydrogen phthalate (C8H5KO4).

Dry for 2 h at 110 ° C ~ 120 ° C before use.

4.3 Potassium dihydrogen phosphate (KH2PO4).

Dry for 2 h at 110 ° C ~ 120 ° C before use.

4.4 Anhydrous disodium hydrogen phosphate (Na2HPO4).

Dry for 2 h at 110 ° C ~ 120 ° C before use.

4.5 Sodium tetraborate (Na2B4O7·10H2O).

Placed in a desiccator with saturated sodium bromide (or sodium chloride plus sucrose) solution (room temperature) for 48 h to make sodium tetraborate the crystal remains stable.

4.6 pH 4.01 (25 ° C) standard buffer solution. c (C8H5KO4) = 0.05 mol/L.

Weigh 10.12 g of potassium hydrogen phthalate (4.2), dissolve in water, and dilute to 1 L in a volumetric flask at 25 °C. and also Standard solutions that meet national standards can be used directly.

4.7 pH 6.86 (25 ° C) standard buffer solution. c (KH2PO4) = 0.025 mol/L, c (Na2HPO4) = 0.025 mol/L.

3.387 g of potassium dihydrogen phosphate (4.3) and 3.533 g of anhydrous sodium hydrogen phosphate (4.4) were weighed and dissolved in water.

Dilute to 1 L in a volumetric flask at 225 °C. Standard solutions that meet national standards can also be used directly.

4.8 pH 9.18 (25 ° C) standard buffer solution. c (Na2B4O7) = 0.01 mol/L.

Weigh 3.80 g of sodium tetraborate (4.5), dissolve in water, dilute to 1 L in a volumetric flask at 25 ° C, in a polyethylene bottle Sealed in the middle. Standard solutions that meet national standards can also be used directly.

Note. The above pH standard buffer solution can be stored in the refrigerator at 4 ° C for 2 to 3 months. When turbidity, mold or precipitation is found, can't continue to use.

5 Instruments and equipment

5.1 pH meter. Accuracy is 0.01 pH unit with temperature compensation.

5.2 Electrode. glass electrode and saturated calomel electrode, or pH composite electrode.

5.3 Magnetic stirrer or horizontal oscillator. with temperature control.

5.4 Soil Screen. Aperture 2 mm (10 mesh).

5.5 Common instruments and equipment used in general laboratories.

6 Samples

7 Analysis steps

8 Results are expressed

The measurement results are retained to 2 decimal places. When the reading is less than 2.00 or greater than 12.00, the results are expressed as pH 12.00.

9 Precision

Six replicates of six samples from Hunan Yellow Soil and Guizhou Purple Soil were separately measured. pH value of Hunan yellow soil the average value is 4.62, the relative standard deviation in the laboratory is 0.12%~1.5%, and the relative standard deviation between laboratories is 2.7%.

The renaturation limit is 0.10, the reproducibility limit is 0.37; the average value of Guizhou purple soil pH is 5.83, the relative standard deviation in the laboratory for the range of 0.30% to 1.5%, the relative standard deviation between laboratories was 2.8%, the repeatability limit was 0.11, and the reproducibility limit was 0.46.

10 Quality Assurance and Quality Control

At least 10% of parallel samples should be determined for each batch of samples. At least 10 sets of parallel pairs should be determined for each batch of less than 10 samples.

kind. The allowable difference between the two parallel determinations is 0.3 pH units.

11 Precautions

11.1 The pH meter should be used and maintained in accordance with the instrument manual.

11.2 Electrodes should be used and maintained in accordance with the electrode instructions.

11.3 Temperature has a certain influence on the determination of soil pH. When measuring, the temperature should be controlled as required.

11.4 During the measurement, insert the electrode into the suspension of the sample, taking care to remove air bubbles from the electrode surface.

4 Appendix A

(informative appendix) Different pH standard buffer solution (25 ° C) Standard buffer Solution standard material name Molecular formula Standard solution concentration (mol·kg-1) Prepare 1 L standard solution Quality of quasi-substance (g) pH 1.68 Potassium tetraethanoate KH3(C2O4)2·2H2O 0.05 12.61 pH 3.56 Potassium hydrogen tartrate KHC4H4O6 25 ° C saturation is about 0.034 >7 pH 4.01 Potassium hydrogen phthalate KHC8H4O4 0.05 10.12 pH 6.86 Disodium hydrogen phosphate Na2HPO4 0.025 3.533 Potassium dihydrogen phosphate KH2PO4 0.025 3.387 pH 7.41 Disodium hydrogen phosphate Na2HPO4 0.03043 4.303 Potassium dihydrogen phosphate KH2PO4 0.008695 1.179 pH 9.18 sodium tetraborate Na2B4O7·10H2O 0.01 3.80 pH 12.46 Calcium hydroxide Ca(OH)2 25 ° C saturation is about 0.020 > 2