HJ 1147-2020Determination of pH value of water quality Electrode method (English PDF)

5.6.2 Standard buffer solution II. c(Na2HPO4)=0.025 mol/L, c(KH2PO4)=0.025 mol/L, pH=6.86

(25°C).

Weigh 3.53 g of anhydrous disodium hydrogen phosphate (5.3) and 3.39 g of potassium dihydrogen phosphate (5.4) and dissolve in water (5.1), Transfer to a 1 L volumetric flask and dilute to the mark. You can also buy a commercially available qualified standard buffer solution and use it according to the instructions.

5.6.3 Standard buffer solution III. c (Na2B4O7) = 0.01 mol/L, pH = 9.18 (25°C).

Weigh 3.80 g of sodium tetraborate (5.5), dissolve it in water (5.1), transfer to a 1 L volumetric flask, and dilute to the mark.

Sealed and stored in a polyethylene bottle. You can also buy a commercially available qualified standard buffer solution and use it according to the instructions.

Note 1.The above pH standard buffer solution can be stored for 2 to 3 months under refrigeration below 4°C. When turbidity, mold or precipitation is found, Cannot continue to use.

Note 2.When the pH value of the tested sample is too high or too low, other standard buffer solutions with similar pH values can be selected. Refer to Appendix A for details.

5.7 pH extensive test paper.

8.1 Preparation before measurement

Activate and maintain the electrode (6.3) according to the instruction manual, and confirm that the instrument is working normally. On-site measurement should understand on-site environmental conditions and the source and nature of the samples, preliminary judgments whether there are strong acid, high electrolyte, low electrolyte, high Interference with fluoride, etc., and prepare accordingly.

8.2 Instrument calibration

8.2.1 Calibration solution

Use pH extensive test paper (5.7) to roughly measure the pH value of the sample, and choose two suitable calibrations according to the pH value of the sample Use standard buffer solution (5.6). The difference in pH between the two standard buffer solutions is about 3 pH units. The sample pH value should be as low as possible Between the two standard buffer solutions pH value range, if it exceeds the range, the sample pH value is at least one of the standard buffer solutions the difference in pH value does not exceed 2 pH units.

8.2.2 Temperature compensation

Manual temperature compensation instrument, adjust the temperature of the standard buffer solution to be consistent with the actual temperature of the sample, use the temperature the meter (6.4) measures and records the temperature. During calibration, set the temperature compensation knob of the acid meter (6.2) to this temperature. With for the instrument with automatic temperature compensation, it is not necessary to keep the standard buffer solution and the sample at the same temperature, follow the instrument instructions operating. See Appendix B for common temperature compensation methods.

Note. The instrument with automatic temperature compensation function must be used for on-site measurement.

8.2.3 Calibration method

Use two-point calibration method, select the calibration mode according to the instrument manual, first use neutral (or weak acid, weak base) standard buffer Solution, and then calibrated with acidic or alkaline standard buffer solution. Refer to the attached table for the pH value of various standard buffer solutions at different temperatures A.2.

a) Immerse the electrode (6.3) in the first standard buffer solution and stir slowly horizontally to avoid air bubbles. Wait until the reading is stable.

After setting, adjust the display value of the instrument to be consistent with the pH value of the standard buffer solution.

b) Rinse the electrode (6.3) with distilled water and absorb the moisture on the electrode surface with the edge of the filter paper, and immerse the electrode (6.3) in the second in a standard buffer solution, stir slowly and horizontally to avoid air bubbles. After the reading is stable, adjust the value of the instrument Consistent with the pH value of the standard buffer solution.

c) Repeat a) operation, after the reading is stable, the difference between the displayed value of the instrument and the pH value of the standard buffer solution should be <=0.05 pH unit, otherwise repeat steps a) and b) until qualified.

Note 1.Multi-point calibration method can also be used. Follow the instrument manual. When measuring actual samples, it is necessary to use similar pH values (not large Verification of certified reference samples or reference materials at 3 pH units.

Note 2.The reading of the pH meter within 1 min changes less than 0.05 pH units to be regarded as stable.

48.3 Sample determination

Rinse the electrode with distilled water and use the edge of the filter paper to absorb the moisture on the surface of the electrode. Take an appropriate amount according to the instrument used during on-site measurement Sample or direct measurement; in the laboratory, pour the sample into the beaker (6.5) along the wall of the cup, and immediately dip the electrode into the sample.

Stir slowly and horizontally to avoid air bubbles. After the reading is stable, write down the pH value. The instrument with automatic reading function can directly Read the data. Rinse the electrode with distilled water after each sample is measured.

9 Results presentation the measurement result keeps one decimal place, and the temperature of the sample is indicated. When the measurement result exceeds the measurement range (0~

14) When it is reported as "strong acid, out of measuring range" or "strong base, out of measuring range".

10 Precision and accuracy

10.1 Precision

The six laboratories tested drinking water source water, landscape surface water, and landscape water with pH values of 8.2, 7.5, 8.3, 8.6, 2.1, and 10.2, respectively.

The unified samples of groundwater, domestic sewage and two kinds of industrial wastewater were subjected to 6 repeated determinations. the range in the laboratory was all 0.1;

The range between laboratories is 0.1~0.2.

10.2 Accuracy

The six laboratories have tested 3 uniform certified standards with pH values of 4.13±0.04, 7.33±0.06 and 9.09±0.07, respectively the sample was tested for 6 times. the error ranges were -0.04~0.02, -0.05~0.04 and -0.05~0; the final error the values are -0.02±0.06, -0.03±0.08 and -0.04±0.04, respectively.

11 Quality Assurance and Quality Control

11.1 The instrument should be calibrated before the determination of each batch of samples. When the pH value of the sample changes significantly or the monitoring site changes New calibration.

11.2 For every 20 consecutive samples or batches (<=20 samples/batch), 1 certified standard sample or standard should be analyzed Quality, the measurement result should be within the guaranteed value range, otherwise it should be re-calibrated and re-measure the batch of samples.

11.3 Every 20 samples or every batch (<=20 samples/batch) should analyze 1 parallel sample. When the pH value is between 6-9 the allowable difference is ±0.1 pH units; when the pH value is less than or equal to 6 or the pH value is >=9, the allowable difference is ±0.2 pH units.

The measurement result is the first measurement value.

12 Waste treatment

The waste generated during the experiment should be collected separately, properly kept, and entrusted to a qualified unit for disposal according to law.

513 Note

13.1 The pH meter (6.2) should be used and maintained according to the instrument manual.

13.2 The electrode (6.3) should be used and maintained according to the instructions.

13.3 In order to reduce the dissolution of acid and alkaline gases in the air, or the volatilization of corresponding substances in the sample, the sampling should not be opened before the determination.

Sample bottle (6.1).

13.4 When measuring strongly alkaline samples with a pH value greater than 10, a polyethylene beaker (6.5) should be used.

13.5 The used standard buffer solution is not allowed to be poured back into the original bottle.

13.6 If there are special needs, the number of significant digits of the result can be determined according to the needs and the accuracy of the instrument.

13.7 If you choose higher-precision instruments and equipment, you need to use a higher-precision standard buffer solution.

The accuracy should meet the requirements of the instrument, see Appendix A for details.

6 Appendix A

(Informative appendix) Standard buffer solution A.1 Composition of standard buffer solution There are 6 kinds of standard buffer solutions, and their composition and the quality of standard substances required to prepare 1 L solution are listed in Table A.1.

Table A.1 Composition of standard buffer solution

A.2 Preparation and storage of standard buffer solution A.2.1 Experimental water. newly prepared distilled water to remove carbon dioxide.

Pour water into the flask, boil for 10 minutes, cover and let it cool. Temporarily use the current system.

A.2.2 Potassium tetraoxalate (KH3C4O8·2H2O).

Dry for 4 h at 51°C~57°C, store in a desiccator for later use.

A.2.3 Potassium hydrogen tartrate (KH5C4O6).

A.2.4 Potassium hydrogen phthalate (C8H5KO4).

Dry for 2 h at 110°C~120°C, and store in a desiccator for later use.

A.2.5 Anhydrous disodium hydrogen phosphate (Na2HPO4).

Dry for 2 h at 110°C~120°C, and store in a desiccator for later use.

A.2.6 Potassium dihydrogen phosphate (KH2PO4).

Dry for 2 h at 110°C~120°C, and store in a desiccator for later use.

A.2.7 Sodium tetraborate (Na2B4O7·10H2O).

Place it in a desiccator with saturated sodium bromide (or sodium chloride and sucrose) solution (room temperature) for 48 hours to make sodium tetraborate

7 The crystal remains stable.

A.2.8 Calcium hydroxide [Ca(OH)2].

A.2.9 Standard buffer solution B1.c (KH3C4O8·2H2O)=0.05 mol/L, pH=1.680 (25°C).

Weigh 12.61 g of potassium tetraoxalate (A.2.2), dissolve in water (A.2.1), transfer to a 1 L volumetric flask at 25°C and Set the volume to the marking line. You can also buy a commercially available qualified standard buffer solution and use it according to the instructions.

A.2.10 Standard buffer solution B3.KH5C4O6 saturated solution, pH=3.559 (25°C).

Weigh about 7 g of potassium hydrogen tartrate (A.2.3), dissolve it in water (A.2.1), and place it in a ground glass bottle at 22°C~28°C Dilute to 1 L, shake vigorously for 20 minutes to 30 minutes, after the solution is clear, take the clear liquid by decantation method for use. You can also buy the city Qualified standard buffer solutions are sold and used in accordance with the instructions.

A.2.11 Standard buffer solution B4.c (C8H5KO4)=0.05 mol/L, pH=4.003 (25°C).

Weigh 10.12 g of potassium hydrogen phthalate (A.2.4), dissolve in water (A.2.1), and transfer to 1 L volume at 25°C Fill the bottle and dilute to the mark. You can also buy a commercially available qualified standard buffer solution and use it according to the instructions.

A.2.12 Standard buffer solution B6.c(Na2HPO4)=0.025 mol/L, c(KH2PO4)=0.025 mol/L, pH=6.864 (25°C).

Weigh 3.533 g anhydrous disodium hydrogen phosphate (A.2.5) and 3.387 g potassium dihydrogen phosphate (A.2.6), and dissolve in water (A.2.1) Transfer to a 1 L volumetric flask at 25°C and dilute to the mark. You can also buy commercially available qualified standard buffer solutions, according to Instructions for use.

A.2.13 Standard buffer solution B9.c (Na2B4O7) = 0.01 mol/L, pH = 9.182 (25°C).

Weigh 3.80 g of sodium tetraborate (A.2.7), dissolve in water (A.2.1), transfer to a 1 L volumetric flask at 25°C and determine Fill it up to the marking line and seal it in a polyethylene bottle. You can also buy a commercially available qualified standard buffer solution and use it according to the instructions.

A.2.14 Standard buffer solution B12.Ca(OH)2 saturated solution, pH=12.460 (25°C).

Weigh about 2 g of calcium hydroxide (A.2.8), dissolve it in water (A.2.1), and dilute in a polyethylene bottle at 22°C~28°C to 1 L, shake vigorously for 20 min to 30 min. After the solution is clarified, take the clear liquid by decantation method for use. You can also buy commercially available Standard buffer solution, use in accordance with the instructions.

Note 1.B9 and B12 are alkaline solutions and should be sealed and stored in polyethylene bottles. In order to prevent B3 solution from becoming moldy, thymol can be added, the dosage is 1 g per liter of solution. The standard buffer solution can be stored for 2 to 3 months in cold storage below 4°C. Found turbidity, moldy or it cannot continue to be used in the event of precipitation.

Note 2.Refer to GB/T 27501-2011 for the preparation and standard values of the above standard buffer solutions. Other commercially available qualified standard buffer solutions can also be purchased.

A.3 pH values of 6 standard buffer solutions the corresponding pH values of each standard buffer solution at different temperatures are listed in Table A.2.According to the measurement needs and the accuracy of the instrument the purity of the reagent and the accuracy of weighing, the uncertainty of the solution prepared by the reference reagent is 0.005 pH units (k=3), which the uncertainty of the solution prepared by other reagents is 0.01 pH unit (k=3).

9 Appendix B

(Informative appendix) Common temperature compensation methods There are two common temperature compensation methods for acidity meters. manual temperature compensation (MTC mode) and automatic temperature compensation (ATC mode).

Manual temperature compensation (MTC mode). first adjust the temperature of the standard buffer solution to be the same as the actual temperature of the sample Yes, use a thermometer to measure and record the temperature. During calibration, set the temperature compensation knob or button of the acidity meter (7.2) to at the actual temperature of the sample, the pH value of the standard buffer solution is set to the pH value at the actual temperature of the sample (see Table A.2). sample the measurement result (indicated value of the instrument) is the pH value of the sample at the actual temperature.

Automatic temperature compensation (ATC mode). There is no need to adjust the standard buffer solution and the sample to the same temperature. During calibration, the built-in temperature probe can automatically measure the temperature of the standard buffer solution, and the pH value of the standard buffer solution is automatically set to this temperature the pH value at temperature (see Table A.2). When measuring the sample, the actual temperature of the sample is automatically measured and the electrode slope is compensated, the measurement result (indicated value of the instrument) is the pH value of the sample at the actual temperature.