HJ 586-2010_English: PDF (HJ586-2010)
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Water quality. Determination of free chlorine and total chlorine. Spectrophotometric method using N, N-diethyl-1, 4-phenylenediamine
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HJ 586-2010
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Standards related to: HJ 586-2010
| Standard ID | HJ 586-2010 (HJ586-2010) | | Description (Translated English) | Water quality. Determination of free chlorine and total chlorine. Spectrophotometric method using N, N-diethyl-1, 4-phenylenediamine | | Sector / Industry | Environmental Protection Industry Standard | | Classification of Chinese Standard | Z16 | | Classification of International Standard | 13.060.01 | | Word Count Estimation | 16,161 | | Date of Issue | 2010-09-20 | | Date of Implementation | 2010-12-01 | | Older Standard (superseded by this standard) | GB/T 11898-1989 | | Quoted Standard | GB/T 5750.10; GB/T 5750.11 | | Drafting Organization | Dalian Municipal Environmental Monitoring Center | | Administrative Organization | Ministry of Environment Protection | | Regulation (derived from) | Department of Environmental Protection Notice No. 68 of 2010 | | Summary | This standard specifies the determination of free chlorine and total chlorine spectrophotometry. This standard applies to surface water, industrial waste, medical waste, sewage, water and sewage water for regeneration of the landscape of free chlorine and total chlorine. This standard does not apply to determination of turbidity or color higher than the water samples. | HJ 586-2010
Water quality.Determination of free chlorine and total chlorine.Spectrophotometric method using N, N-diethyl-1, 4-phenylenediamine
National Environmental Protection Standard of the People's Republic
Replace GB 11898-89
Determination of free chlorine and total chlorine in water
N,N-diethyl-1,4-phenylenediamine spectrophotometry
Water quality-Determination of free chlorine and total chlorine-
Spectrophotonetric method using N,N-diethyl-1,4-phenylenediamine
Released on.2010-09-20
2010-12-01 Implementation
Ministry of Environmental Protection released
Ministry of Environmental Protection
announcement
No. 68 of.2010
In order to implement the "Environmental Protection Law of the People's Republic of China", protect the environment, and protect human health, we now approve the "environmental air benzene series"
Five standards, such as solid adsorption/thermal desorption-gas chromatography, are considered as national environmental protection standards and are released.
The standard name and number are as follows.
I. Determination of Benzene in Ambient Air Solid Adsorption/Thermal Desorption-Gas Chromatography (HJ 583-2010);
2. Determination of Benzene in Ambient Air Activated Carbon Adsorption/Carbon Disulfide Desorption - Gas Chromatography (HJ 584-2010);
3. Determination of free chlorine and total chlorine in water, N,N-diethyl-1,4-phenylenediamine titration method (HJ 585-2010);
V. "Determination of water quality atrazine by high performance liquid chromatography" (HJ 587-2010).
The above standards have been implemented since December 1,.2010 and published by the China Environmental Science Press. The standard content can be found on the website of the Ministry of Environmental Protection.
From the date of implementation of the above standards, the following four national environmental protection standards approved and issued by the former National Environmental Protection Agency shall be abolished.
The name and number are as follows.
I. Determination of Air Quality, Toluene, Xylene and Styrene by Gas Chromatography (GB/T 14677-93);
2. Determination of Air Quality Styrene by Gas Chromatography (GB/T 14670-93);
3. Determination of free chlorine and total chlorine in water. N,N-diethyl-1,4-phenylenediamine titration method (GB 11897-89);
4. Determination of free chlorine and total chlorine in water quality N,N-Diethyl-1,4-phenylenediamine spectrophotometric method (GB 11898-89).
Special announcement.
September 20,.2010
Content
Foreword..iv
1 Scope..1
2 Normative references..1
3 Terms and Definitions.1
4 principle of the method..2
5 interference and elimination. 2
6 reagents and materials. 2
7 instruments and equipment.4
8 samples.4
9 Analysis steps..4
10 Results calculation and representation 5
11 Precision and Accuracy 6
12 Quality Assurance and Quality Control.6
13 Notes 6
Appendix A (Normative) Determination of free chlorine and total chlorine in water - Determination of N,N-diethyl-1,4-phenylenediamine.
Appendix B (Normative) Determination of three forms of combined chlorine in the form of monochloramine, dichloramine and nitrogen trichloride 10
Iv
Foreword
To protect the environment and protect the human body in order to implement the Environmental Protection Law of the People's Republic of China and the Law of the People's Republic of China on Water Pollution Prevention and Control
This standard is developed for the determination of free chlorine and total chlorine in water.
This standard specifies the determination of free water in landscape water for the determination of surface water, industrial wastewater, medical wastewater, domestic sewage, water and sewage.
N,N-Diethyl-1,4-phenylenediamine spectrophotometry and on-site determination of chlorine and total chlorine.
This standard is for the determination of free chlorine and total chlorine in water. N,N-Diethyl-1,4-phenylenediamine spectrophotometry (GB 11898-89)
Revision.
This standard was first published in 1989. The original standard was drafted. Anhui Environmental Monitoring Center, China Academy of Preventive Medicine Environmental Health
Health Monitoring Institute and Anhui Wuhu Environmental Monitoring Center Station. This is the first revision. The main contents of the revision are as follows.
- Revised the scope of application of the method;
-- Increased the preservation method of the sample and modified the amount of buffer solution added;
- Adjusted the measurement wavelength;
-- Increased the low concentration calibration curve and reduced the detection limit of the method for determining free chlorine and total chlorine in surface water;
-- Added precautionary clauses;
-- Added on-site measurement methods for free chlorine and total chlorine.
From the date of implementation of this standard, the national environmental protection standard “Water” approved and issued by the former National Environmental Protection Agency on December 25, 1989
Determination of free chlorine and total chlorine N,N-diethyl-1,4-phenylenediamine spectrophotometry (GB 11898-89) abolished.
Appendix A and Appendix B of this standard are normative appendices.
This standard was formulated by the Science and Technology Standards Department of the Ministry of Environmental Protection.
This standard is mainly drafted by. Dalian Environmental Monitoring Center.
This standard is verified by. Liaoning Provincial Environmental Monitoring Experimental Center, Anshan Environmental Monitoring Center, Yingkou Environmental Monitoring Center, Shenyang City
Environmental Monitoring Center and Jinzhou Environmental Monitoring Center.
This standard was approved by the Ministry of Environmental Protection on September 20,.2010.
This standard has been implemented since December 1,.2010.
This standard is explained by the Ministry of Environmental Protection.
Determination of free chlorine and total chlorine in water
N,N-diethyl-1,4-phenylenediamine spectrophotometry
Warning. Mercury salt is a highly toxic chemical. Wear protective equipment as required to avoid contact with skin and clothing. Waste after inspection
The liquid should be properly and safely handled.
1 Scope of application
This standard specifies the spectrophotometric method for the determination of free chlorine and total chlorine in water.
This standard applies to free chlorine in landscape water reclaimed from surface water, industrial wastewater, medical wastewater, domestic sewage, intermediate water and sewage.
Determination of total chlorine. This standard does not apply to the determination of turbid or high chroma water samples.
For high concentration samples, using a 10 mm cuvette, the detection limit (in terms of Cl2) of this method is 0.03 mg/L, the measurement range (to
The Cl2 count is 0.12 to 1.50 mg/L. For low concentration samples, using a 50 mm cuvette, the detection limit of this method (in terms of Cl2) is
0.004 mg/L, the measurement range (in terms of Cl2) is 0.016 to 0.20 mg/L.
For samples with free chlorine or total chlorine concentration above the upper limit of the method, the sample can be measured after appropriate dilution.
On-site determination of free chlorine and total chlorine in water was carried out in accordance with Appendix A.
2 Normative references
The contents of this standard refer to the terms in the following documents. For undated references, the valid version applies to this standard.
GB/T 5750.10 Standard Test Method for Drinking Water Standards for disinfection by-products
GB/T 5750.11 Standard Test Method for Drinking Water Standards
3 Terms and definitions
The following terms and definitions apply to this standard.
3.1
Free chlorine free chlorine
Refers to chlorine in the form of hypochlorous acid, hypochlorite ions and dissolved elemental chlorine.
3.2
Chlorine combined chlorine
Refers to chlorine in the form of chloramines and organic chloramines.
3.3
Total chlorine total chlorine
Refers to chlorine in the form of "free chlorine" or "chlorinated chlorine", or both.
3.4
Chloramine chloramines
A derivative in which one, two or three hydrogen atoms of ammonia are replaced by chlorine atoms as determined by the method (eg monochloramine, dichloramine, nitrogen trichloride)
And chlorinated derivatives of organic nitrogen compounds.
The composition of free chlorine and total chlorine is shown in Table 1.
Table 1 Nouns and their composition
Noun composition
Free chlorine (free residual chlorine)
Active free chlorine elemental chlorine, hypochlorous acid
Potential free chlorine hypochlorite
Total chlorine (total residual chlorine) elemental chlorine, hypochlorous acid, hypochlorite, chloramine
4 Principle of the method
4.1 Determination of free chlorine
At pH 6.2-6.5, free chlorine reacts directly with N,N-diethyl-1,4-phenylenediamine (DPD) to form a red complex.
The absorbance was measured at a wavelength of 515 nm.
Since the free chlorine standard solution is unstable and difficult to obtain, this standard uses a iodine molecule or [I3]− instead of free chlorine as a calibration curve. Potassium iodate
Benchmarking, under acidic conditions, reacts with potassium iodide as follows. IO3− 5I− 6H =3I2 3H2O, I2 I−=[I3]−, the resulting iodine molecule or
[I3] − A color reaction with DPD, the ratio of the amount of iodine molecules to the amount of chlorine molecules is 1.1.
4.2 Determination of total chlorine
At pH 6.2-6.5, elemental chlorine, hypochlorous acid, hypochlorite and chloramine react with DPD in the presence of excess potassium iodide.
A red compound was formed and its absorbance was measured at a wavelength of 515 nm to determine total chlorine.
5 interference and elimination
5.1 Interference from other chlorine compounds
Chlorine dioxide interferes with the determination of free chlorine and total chlorine, and chlorite interferes with the determination of total chlorine. Chlorine dioxide and chlorite
It can be corrected by measuring its concentration. For the determination method, see GB/T 5750.11 and GB/T 5750.10.
High concentrations of monochloramine interfere with the determination of free chlorine. Can be added by adding sodium arsenite solution (6.13) or thioacetamide solution
(6.13) Elimination of interference with monochloramine, determination of monochloramine in accordance with Appendix B.
5.2 Interference between manganese oxide and hexavalent chromium
Manganese oxide and hexavalent chromium can interfere with the determination. The interference can be eliminated by measuring the concentration of manganese oxide and hexavalent chromium.
9.2.
5.3 Interference of other oxides
This method interferes in the presence of the following oxidizing agents. bromine, iodine, bromoamine, iodine, ozone, hydrogen peroxide, chromate, oxidation
Manganese, hexavalent chromium, nitrite, copper ions (Cu2) and iron ions (Fe3). Among them Cu2 (< 8 mg/L) and Fe3 (< 20 mg/L)
Interference can be masked by Na2-EDTA in buffer solution and DPD solution, other oxides interfere with sodium arsenite solution (6.13) or
The thioacetamide solution (6.13) was eliminated. The chromate interference can be eliminated by the addition of cesium chloride.
6 reagents and materials
Unless otherwise stated, analytically pure reagents that meet national standards were used for the analysis.
6.1 Experimental water. It is deionized water or double distilled water containing no chlorine and reducing substances. The experimental water needs to pass the inspection before it can be used.
Test method. Add 100 ml of water to be tested and 1.0 g of potassium iodide (6.3) to the first 250 ml Erlenmeyer flask and mix. After 1 min,
Add 5.0 ml of phosphate buffer solution (6.11) and 5.0 ml of DPD solution (6.12); then add to the second 250 ml Erlenmeyer flask.
100 ml of water to be tested and 2 drops of sodium hypochlorite solution (6.4). After 2 min, add 5.0 ml phosphate buffer solution (6.11) and 5.0 ml DPD
Solution (6.12).
The first bottle does not show color, and the second bottle should be pink. Otherwise, the experimental water should be dechlorinated by treatment with activated carbon column and pressed.
The steps are checked for quality and can be used until qualified.
6.2 Concentrated sulfuric acid. ρ = 1.84 g/ml.
6.3 Potassium iodide (KI). crystal.
6.4 sodium hypochlorite solution. ρ (Cl2) ≈ 0.1 g/L
It is diluted by a concentrated solution of sodium hypochlorite (trade name, Antifumin).
6.5 sulfuric acid solution. c(H2SO4)=1.0 mol/L
In 800 ml water (6.1), carefully add 54.0 ml of concentrated sulfuric acid (6.2) with constant stirring. After cooling, transfer the solution to 1 000 ml.
In the volumetric flask, add water (6.1) to the mark and mix.
6.6 sodium hydroxide solution. c (NaOH) = 2.0 mol/L
Weigh 80.0 g of sodium hydroxide, dissolve in 800 ml of water (6.1), transfer the solution to a 1 000 ml volumetric flask, add water (6.1)
Go to the marking line and mix.
6.7 sodium hydroxide solution. c (NaOH) = 1.0 mol/L
Weigh 40.0 g of sodium hydroxide, dissolve in 500 ml of water (6.1), transfer the solution to a 1 000 ml volumetric flask, add water (6.1)
Go to the marking line and mix.
6.8 Potassium iodate standard stock solution. ρ(KIO3)=1.006 g/L
Weigh the superior grade pure potassium iodate (previously dried at 120 ~ 140 ° C for 2 h) 1.006 g, dissolved in water (6.1), transferred to 1 000 ml
Volumetric flask, add water (6.1) to the marking line and mix.
6.9 Potassium iodate standard use solution I. ρ(KIO3)=10.06 mg/L
Pipette 10.00 ml of potassium iodate standard stock solution (6.8) into a 1 000 ml brown volumetric flask, add about 1 g of potassium iodide (6.3), add water (6.1)
Go to the marking line and mix. Available now. The 1.00 ml standard solution contains 10.06 μg of KIO3, which is equivalent to 0.141 μmol (10.0 μg) of Cl2.
6.10 Potassium iodate standard use solution II. ρ (KIO3) = 1.006 mg/L
Pipette 10.00 ml of potassium iodate standard solution I (6.9) into a 100 ml brown volumetric flask, add water (6.1) to the mark, and mix. Pro
Use the match now. The 1.00 ml standard solution contains 1.006 μg of KIO3, which is equivalent to 0.014 μmol (1.0 μg) of Cl2.
6.11 Phosphate buffer solution. pH=6.5
Weigh 24.0 g of anhydrous sodium hydrogen phosphate (Na2HPO4) or 60.5 g of disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), and
46.0 g potassium dihydrogen phosphate (KH2PO4), dissolved in water, and added 100 ml of 8.0 g/L disodium EDTA dihydrate
(C10H14N2O8Na2·2H2O) solution or 0.8 g EDTA disodium solid, transfer to a 1 000 ml volumetric flask, add water (6.1) to the mark,
Mix well. If necessary, 0.020 g of mercuric chloride can be added to prevent mold propagation and interference with traces of iodide in the reagents on free chlorine testing.
6.12 N,N-diethyl-1,4-phenylenediamine sulfate (DPD) solution. ρ[NH2-C6H4-N(C2H5)2·H2SO4]=1.1 g/L
2.0 ml of sulfuric acid (6.2) and 25 ml of 8.0 g/L dihydrate EDTA disodium solution or 0.2 g EDTA disodium solid, plus
Mix into 250 ml of water (6.1) to make a mixed solution. Add 1.1 g of anhydrous DPD sulfate or 1.5 g of pentahydrate to the above mixed solution
In the solution, transfer to a 1 000 ml brown volumetric flask, add water (6.1) to the mark and mix. The solution was placed in a brown reagent bottle and stored at 4 °C.
If the solution changes color after standing for a long time, it should be reconstituted.
Note. DPD sulphate can also be replaced by 1.1 g DPD oxalate or 1.0 g DPD hydrochloride.
6.13 Sodium arsenite solution or thioacetamide solution. ρ(NaAsO2)=2.0 g/L, ρ(CH3CSNH2)=2.5 g/L.
7 Instruments and equipment
7.1 Visible spectrophotometer. with 10 mm and 50 mm cuvettes.
7.2 Balance. The accuracy is 0.1 g and 0.1 mg, respectively.
7.3 Common instruments and equipment used in general laboratories.
Note. The glassware in the experiment should be soaked in sodium hypochlorite solution (6.4) for 1 h, then rinsed thoroughly with water (6.1).
8 samples
8.1 Sample Collection
Free chlorine and total chlorine are unstable, samples should be measured on site as far as possible, and the on-site measurement method is shown in Appendix A. If the sample cannot be measured on site, it is required
Add the fixative to the sample. A sample volume of 1% NaOH solution (6.6) can be pre-filled into a brown glass bottle to collect the water sample.
Fill the sample bottle and immediately cap it tightly and seal it to prevent the water sample from coming into contact with the air. If the sample is acidic, increase the amount of NaOH solution added.
Make sure the pH of the water sample is greater than 12.
8.2 Sample storage
The water samples were transported in a freezer, stored in a laboratory at 4 ° C, protected from light, and measured within 5 days.
9 Analysis steps
9.1 Drawing of the calibration curve
9.1.1 Calibration curve drawing of high concentration samples
Take 0.00, 1.00, 2.00, 3.00, 5.00, 10.0, and 15.0 ml of potassium iodate standard solution I (6.9) to 100 ml.
In the measuring flask, add an appropriate amount (about 50 ml) of water (6.1). 1.0 ml of sulfuric acid solution (6.5) was added to each volumetric flask. After 1 min, to each capacity
Add 1 ml of NaOH solution (6.7) to the bottle and dilute to the mark with water (6.1). The chlorine concentration ρ(Cl2) in each volumetric flask is 0.00, respectively.
0.10, 0.20, 0.30, 0.50, 1.00, and 1.50 mg/L.
Add 15.0 ml of phosphate buffer solution (6.11) and 5.0 ml of DPD solution (6.12) to each other in a 250 ml Erlenmeyer flask for 1 min.
The above standard series solution was added to the Erlenmeyer flask, and after mixing, the absorbance of each solution was measured with a 10 mm cuvette at a wavelength of 515 nm.
Colorimetric analysis was completed in 60 min.
The absorbance value is corrected to zero on the ordinate, and the corresponding chlorine concentration ρ(Cl2) is plotted on the abscissa to draw a calibration curve.
9.1.2 Calibration curve drawing of low concentration samples
Take 0.00, 2.00, 4.00, 8.00, 12.0, 16.0 and 20.0 ml of potassium iodate standard use solution II (6.10) in 100 ml capacity respectively.
In the measuring flask, add an appropriate amount (about 50 ml) of water (6.1). 1.0 ml of sulfuric acid solution (6.5) was added to each volumetric flask. After 1 min, to each capacity
Add 1 ml of NaOH solution (6.7) to the bottle and dilute to the mark with water (6.1). The chlorine concentration ρ(Cl2) in each volumetric flask is 0.00, respectively.
0.02, 0.04, 0.08, 0.12, 0.16 and 0.20 mg/L.
Add 15.0 ml of phosphate buffer solution (6.11) and 1.0 ml DPD solution (6.12) to each other in a 250 ml Erlenmeyer flask for 1 min.
Add the above standard series solution into the Erlenmeyer flask, mix it, and measure the solution with a 50 mm cuvette at a wavelength of 515 nm.
Absorbance, colorimetric analysis was completed in 60 min.
The absorbance value is corrected to zero on the ordinate, and the corresponding chlorine concentration ρ(Cl2) is plotted on the abscissa to draw a calibration curve.
9.2 Determination of free chlorine
In a 250 ml Erlenmeyer flask, add 15.0 ml phosphate buffer solution (6.11), 5.0 ml DPD solution (6.12) and 100 ml.
The water sample (or diluted water sample) was measured for absorbance under the same conditions as the calibration curve. Calculate the quality with the absorbance value after blank correction
The concentration is ρ1.
For samples containing manganese oxide and hexavalent chromium, the interference can be eliminated by measuring the content of both. Take 100 ml sample in 250 ml conical flask
Add 1.0 ml of sodium arsenite solution (6.13) or thioacetamide solution (6.13) and mix. Add 15.0 ml phosphate buffer solution
(6.11) and 5.0 ml DPD solution (6.12), the absorbance was measured, and the mass concentration ρ3 was recorded, which was equivalent to the interference of manganese oxide and hexavalent chromium. If
The water sample should be diluted, and the manganese oxide and hexavalent chromium interference of the diluted sample should be determined.
Note. When measuring the free chlorine in low concentration samples, 1.0 ml DPD solution (6.12) should be added.
9.3 Determination of total chlorine
In a 250 ml Erlenmeyer flask, add 15.0 ml phosphate buffer solution (6.11), 5.0 ml DPD solution (6.12), 100 ml.
Mix the water sample (or diluted water sample) with 1.0 g potassium iodide (6.3). The absorbance was measured under the same conditions as in the drawing of the calibration curve. use
The absorbance value after the blank correction calculates the mass concentration ρ2.
For samples containing manganese oxide and hexavalent chromium, the interference can be eliminated by measuring the content. For the determination method, see 9.2.
Note. For the determination of total chlorine in low concentration samples, 1.0 ml DPD solution (6.12) should be added.
9.4 Blank test
The sample was replaced with water (6.1) and measured according to 9.2 and 9.3. Blank samples should be measured in the same batch as the sample.
10 Calculation and representation of results
10.1 Calculation of free chlorine
The mass concentration ρ(Cl2) of free chlorine is calculated according to the formula (1).
2 1 3(Cl ) ( ) fρ ρ ρ= − × (1)
Where. - the mass concentration of free chlorine in the water sample (in terms of Cl2), mg/L; 2 (Cl ) ρ
Ρ1-- mass concentration of free chlorine in the sample (in terms of Cl2), mg/L;
Ρ3--determine the mass concentration of chlorine equivalent to the interference of manganese oxide and hexavalent chromium, mg/L, if manganese oxide and hexavalent chromium are not present,
Ρ3=0 mg/L;
f--Water sample dilution ratio.
10.2 Calculation of total chlorine
The total chlorine concentration ρ(Cl2) is calculated according to the formula (2).
2 2 3(Cl ) ( ) fρ ρ ρ= − × (2)
Where. - the mass concentration of total chlorine in the water sample (in terms of Cl2), mg/L; 2 (Cl ) ρ
Ρ2 - the mass concentration of total chlorine in the sample (in terms of Cl2), mg/L;
Ρ3--determine the mass concentration of chlorine equivalent to the interference of manganese oxide and hexavalent chromium, mg/L, if manganese oxide and hexavalent chromium are not present,
Ρ3=0 mg/L;
f--Water sample dilution ratio.
10.3 Results are expressed
When the measurement result is less than 0.01 mg/L, it is retained to three decimal places; when it is greater than or equal to 0.01 mg/L and less than 10 mg/L,
Leave two decimal places; when it is greater than or equal to 10 mg/L, keep three significant digits.
11 Precision and accuracy
11.1 Precision
Five laboratories tested uniform samples containing potassium iodate at concentrations of 0.15, 0.76, and 1.36 mg/L.
The relative standard deviations in the experimental room were. 8.9% to 11.6%, 2.5% to 3.9%, and 1.3% to 2.2%;
The relative standard deviations between laboratories were. 2.7%, 8.7%, 0.4%;
The repeatability limits were. 0.05 mg/L, 0.07 mg/L, and 0.07 mg/L;
The reproducibility limits were. 0.05 mg/L, 0.07 mg/L, and 0.06 mg/L, respectively.
11.2 Accuracy
Five laboratories used sodium hypochlorite to measure the three actual samples from tap water, medical wastewater and domestic sewage.
The recoveries of spiked standards were. 96.7%~102%, 99.4%~104%, 98.3%~103%;
The final recoveries of the spiked recovery were. 99.2% ± 4.9%, 103% ± 3.8%, and 102% ± 4.0%.
In the same laboratory, the standard solutions containing potassium iodate concentrations of 0.02, 0.04, 0.08, and 0.12 mg/L were measured in parallel six times, as opposed to
The standard deviations were 11.1%, 6.6%, 3.8%, and 2.0%, respectively; the relative errors were 10.0%, 10.0%, 5.0%, and 2.5%, respectively.
12 Quality Assurance and Quality Control
12.1 The correlation coefficient of the calibration curve regression equation should be greater than or equal to 0.999.
12.2 Each batch of samples shall be provided with an intermediate checkpoint. The relative error between the measured value of the intermediate checkpoint and the corresponding point of the calibration curve shall not exceed
15%.
13 Precautions
13.1 When the sample is measured in the field, if the sample is too acidic, too alkaline or the salt concentration is high, increase the amount of phosphate buffer solution added to confirm
The pH of the test sample is between 6.2 and 6.5. When measuring, the sample should avoid glare, shaking and warming.
13.2 If the sample needs to be transported back to the laboratory for analysis, for a very acidic water sample, the amount of fixative NaOH solution should be increased to make the sample
pH>12; if the sample NaOH solution is added in a volume greater than 1% of the sample volume, the sample volume should be corrected; for a very alkaline water sample
(pH>12), no need to add fixative, the amount of phosphate buffer solution...
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