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HJ 962-2018: Soil - Determination of pH - Potentiometry
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Soil - Determination of pH - Potentiometry
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HJ 962-2018
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Basic data | Standard ID | HJ 962-2018 (HJ962-2018) | | Description (Translated English) | Soil - Determination of pH - Potentiometry | | Sector / Industry | Environmental Protection Industry Standard | | Classification of Chinese Standard | Z18 | | Word Count Estimation | 8,844 | | Date of Issue | 2018-07-29 | | Date of Implementation | 2019-01-01 | | Regulation (derived from) | Ministry of Ecology and Environment Announcement No. 27 of 2018 | | Issuing agency(ies) | Ministry of Ecology and Environment | HJ 962-2018: Soil - Determination of pH - Potentiometry---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Soil - Determination of pH - Potentiometry
National Environmental Protection Standard of the People's Republic
Soil pH measurement potential method
Published on.2018-07-29
2019-01-01 Implementation
Ministry of Ecology and Environment released
i directory
Foreword.ii
1 Scope..1
2 Normative references..1
3 method principle..1
4 Reagents and materials.1
5 instruments and equipment. 2
6 samples. 2
7 Analysis steps..2
8 results indicate ..3
9 precision 3
10 Quality Assurance and Quality Control.3
11 Notes 3
Appendix A (informative) different pH standard buffer solution (25 ° C) 4
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
6.1 Sample collection and preservation
Soil samples were collected and stored in accordance with the relevant regulations of HJ/T 166.
6.2 Preparation of samples
Preparation of soil samples in accordance with HJ/T 166, including air drying, shrinkage, comminution and sieving of samples
(5.4). When the prepared sample is not immediately measured, it should be sealed and stored to protect it from atmospheric ammonia and acid gases.
Avoid the effects of sun exposure, high temperature and humidity.
6.3 Preparation of samples
Weigh 10.0 g of soil sample into a 50 ml tall beaker or other suitable container and add 25 ml of water (4.1).
After sealing the container with a sealing film or plastic wrap, stir vigorously for 2 min with a magnetic stirrer (5.3) or with a horizontal shaker (5.3)
Vibrate vigorously for 2 min. After standing for 30 min, the measurement was completed within 1 h.
7 Analysis steps
7.1 Calibration
The pH meter is calibrated using at least two pH standard buffer solutions. First use pH 6.86 (25 ° C) standard buffer solution
(4.7), then use standard buffer solution (4.6) of pH 4.01 (25 °C) or standard buffer solution of pH 9.18 (25 °C) (4.8)
calibration. The calibration steps are as follows.
a) Place the beaker containing the standard buffer solution and the built-in stirrer on the magnetic stirrer (5.3) to turn on the magnetic stirring.
Device.
b) control the temperature of the standard buffer solution at (25 ± 1) ° C, measure the temperature of the standard buffer solution with a thermometer, and
The temperature compensation knob of the 3 pH meter is adjusted to this temperature. For instruments with automatic temperature compensation, this step can be omitted.
c) Insert the electrode into the standard buffer solution. After the reading is stable, adjust the instrument value to the pH of the standard buffer solution.
The values are the same. Repeat steps a and b to calibrate the pH meter with another standard buffer solution. The instrument indicates the standard buffer solution.
The difference in pH should be ≤ 0.02 pH units. Otherwise it should be recalibrated.
Note. Two standard buffer solutions for calibrating pH, the pH of one of the standard buffer solutions should not differ from the pH of the soil by more than 2
One pH unit. If it is out of range, other pH standard buffer solutions can be selected, see Appendix A.
7.2 Determination
The temperature of the control sample (6.3) is (25 ± 1) ° C, and the difference from the temperature of the standard buffer solution should not exceed 2 ° C. will
Insert the electrode into the suspension of the sample. The electrode probe is immersed in the vertical depth of the suspension at 1/3~2/3, and the sample is gently shaken.
After the reading has stabilized, record the pH. Immediately after each sample is measured, rinse the electrode with water and use filter paper to remove the external water from the electrode.
Drain and measure the next sample.
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
< 2.00 or 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
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