GB/T 11742-1989 Standard method for the examination of hydrogen sulfide in the atmosphere of residential areas - Methylene blue spectrophotometric method
Some standard content:
National Standard of the People's Republic of China
Hygienic examination of hydrogen sulfide in air of residential areas
Standard method for hygienic examination ofhydrogen sulfide in air of residential areas -Methylene blue spectrophotometric method1 Subject content and scope of application
GB 11742-89
This standard specifies the determination of hydrogen sulfide concentration in air of residential areas by methylene blue spectrophotometric method. This standard is applicable to the determination of hydrogen sulfide concentration in air of residential areas, and also to the determination of hydrogen sulfide concentration in air vapor in indoor and public places.
1.1 Sensitivity
10mL of absorption liquid containing 1μg hydrogen sulfide should have an absorbance of 0.155±0.010. 1.2 Lower limit of detection
The lower limit of detection is 0.15μg/10mL. If the sampling volume is 30L, the minimum detection concentration is 0.005mg/m2. 1.3 Measurement range
The measurement range is 0.15~4μg hydrogen sulfide in 10mL sample solution. If the sampling volume is 30L, the measurable concentration range is 0.005~0.13mg/m2. If the hydrogen sulfide concentration is greater than 0.13mg/m2, the sampling volume should be appropriately reduced, or part of the sample solution should be taken for analysis.
1.4 Interference and elimination
Since hydrogen sulfide is easily oxidized under light, it should be protected from light during sampling and before sample analysis. The sampling time should not exceed 1h, and color analysis should be performed within 6h after sampling. The SO2 concentration in the air is less than 1mg/m3, and the NOz concentration is less than 0.6mg/m3, which will not interfere with the determination. 2 Principle
Hydrogen sulfide in the air is absorbed by the alkaline cadmium hydroxide suspension to form cadmium sulfide precipitation. Adding polyvinyl alcohol ammonium phosphate to the absorption solution can reduce the photodecomposition of cadmium sulfide. Then, in sulfuric acid solution, hydrogen sulfide reacts with p-aminodimethylaniline solution and ferric chloride solution to generate methylene blue. According to the color depth, colorimetric quantification is performed. 3 Reagents and materials
The purity of the reagents used in this method is analytically pure, and the water used is double distilled water, that is, a small amount of barium hydroxide and potassium permanganate are added to the first distilled water and then distilled.
3.1 Absorption solution: Weigh 4.3g of barium sulfate (3CdSO·8HO), 0.3g of sodium hydroxide and 10g of polyvinyl alcohol ammonium phosphate and dissolve them in water respectively. When using, mix the three solutions, shake vigorously until completely miscible, and then dilute with water to 1L. This solution is a fish-colored suspension. Shake vigorously before use and measure it. It can be stored in the refrigerator for one week. 3.2 p-Aminodimethylaniline solution:
3.2.1 Stock solution: Measure 50mL of concentrated sulfuric acid and slowly add it into 30mL of water. After cooling, weigh 12g of p-hydrogen dimethylaniline hydrochloride (N,N-dimethyl-p-phenylenediamine dihydrochloride, (CH,)2NC.H,·2HCIJ and dissolve it in sulfuric acid solution. Place it in a refrigerator and it can be stored for 1 year. Approved by the Ministry of Health of the People's Republic of China on September 21, 1989 156
Implemented on July 1, 1990
GB 11742—89
3.2.2 Working solution: Measure 2.5mL of the stock solution and dilute it to 100mL with 1+1 sulfuric acid solution. 3.3 Ferric chloride solution: Weigh 100g of ferric chloride (FeCl3*6H2O) and dissolve it in water, dilute to 100mL. If there is precipitation, it needs to be filtered before use.
3.4 Mixed color developing solution: When using, mix 1mL of p-aminodimethylaniline working solution and 1 drop (0.04mL) of ferric chloride solution. This mixed solution should be prepared before use. If precipitation is generated, it should be discarded. 3.5 Diammonium hydrogen phosphate solution Solution: Weigh 40g of diammonium hydrogen phosphate [(NH,)2HPO4] and dissolve it in water, and dilute to 100mL. 3.6 0.0 100N sodium thiosulfate standard solution: Accurately pipette 100mL of 0.1000N sodium thiosulfate standard solution and dilute to 1L with freshly boiled and cooled water. For preparation and concentration calibration methods, see Appendix A (Supplement). 3.7 0.10N iodine solution: Weigh 40g of potassium iodide and dissolve it in 25mL of water, then weigh 12.7g of iodine and dissolve it in potassium iodide solution and dilute to 1L with water. Transfer to a brown bottle and store in a dark place. 3.8 0.0 1N iodine solution: Accurately pipette 1 00mL 0.10N iodine solution in a 1L brown volumetric flask, weigh another 18g potassium iodide and dissolve it in a small amount of water, transfer it to the volumetric flask, and dilute it to the scale with water. 3.9 0.5% starch solution: weigh 0.5g soluble starch, add 5mL water to make a paste, then add 100mL boiling water and boil for 2-3 minutes until the solution is transparent, cool, and prepare it before use. 3.10 1+1 hydrochloric acid solution: mix 50mL concentrated hydrochloric acid with 50mL water. 3.11 Standard solution: Take sodium sulfide crystals (Na2S·9H20), wash the surface with a small amount of water, and dry it with filter paper. Weigh 0.71g sulfur Sodium sulfide crystals, dissolve in freshly boiled and cooled water, and then dilute to 1L. Use the following iodine titration method to calibrate the concentration. After calibration, immediately dilute with freshly boiled and cooled water to 1.00mL of 5μg hydrogen sulfide standard solution. Since sodium sulfide is extremely unstable in aqueous solution, a standard curve should be made immediately after dilution. The standard solution must be freshly prepared each time, calibrated now, and used now. Calibration method: Accurately pipette 20.00mL of 0.01N iodine standard solution into a 250mL iodine volumetric bottle. Add 90mL of water, add 1mL of 1+1 hydrochloric acid solution, accurately add 10.00mL of sodium sulfide solution, mix well, and place in the dark for 3min. Then titrate with 0.0100N sodium thiosulfate standard solution until light yellow, add 1mL of newly prepared 0.5% starch solution to turn blue, rinse the inner wall of the bottle with a small amount of water, and continue titrating until the blue color just disappears (due to the generation of sulfur, the solution is slightly mixed. At this time, pay special attention to the color mutation at the titration end point). Record the volume of sodium thiosulfate standard solution used. At the same time, take another 10mL of water for blank titration. The titration steps are exactly the same. Record the volume of sodium thiosulfate standard solution used for blank titration. Repeat the sample titration and blank titration twice. The volume error of sodium thiosulfate used in the two titrations should not exceed 0.05mL. The concentration of hydrogen sulfide is calculated using formula (1). V2-Vi
Where: °C-concentration of hydrogen sulfide, mg/mL, XN× 17
V2-—volume of sodium thiosulfate used in blank titration, mLV, —volume of sodium thiosulfate used in sample titration, mL, N—equivalent concentration of sodium thiosulfate standard solution; 17-—equivalent amount of hydrogen sulfide.
3.12 Hydrogen sulfide permeation tube: Purchase a permeation tube calibrated by the national metrology department using the weighing method. The permeability range is 0.02~0.5μg/min and the uncertainty is 2%.
4 Instruments and equipment
4.1 Large bubble absorption tube: with 10mL scale line and equipped with black light-proof cover. 4.2 Air sampler: flow range 0.2～2L/min, stable flow. When in use, use soap film flowmeter to calibrate the flow of the sampling series before and after sampling, and the flow error should be less than 5%. 4.3 Stoppered colorimetric tube; 10mL.
4.4 Spectrophotometer: use 20mm colorimetric III, measure absorbance at wavelength 665nm. 4.5 Permeation tube gas distribution device: the temperature of the permeation tube constant temperature bath should be controlled within ±0.1C, and the gas flow error in the gas distribution system should be less than 2% (refer to GB5275 "Preparation of mixed gas for gas analysis standard"). 157
5 Sampling
GB11742-89
Use a large bubble absorption tube filled with 10mL absorption liquid to collect 30L of air sample at a flow rate of 0.5-1.5L/min in the dark. According to the concentration of hydrogen sulfide on site, select the sampling flow rate so that the maximum sampling time does not exceed 1h. The sampled sample should also be placed in a dark place and color developed within 6h, or add color developing liquid on site, bring back to the laboratory, and perform colorimetric determination on the same day. Record the temperature and atmospheric pressure during sampling. 6 Analysis steps
6.1 Drawing of standard curve
6.1.1 Use standard solution to draw standard curve: Prepare standard series tubes according to the table below, add absorption solution first, then add standard solution, and immediately invert to mix. Hydrogen sulfide standard series
Absorption solution, mL
Standard solution, mL
Hydrogen sulfide content, ug
Immediately add 1mL of mixed color solution to each tube, cover and invert, slowly mix evenly, and place for 30 minutes. Add 1 drop of disodium hydrogen phosphate solution and shake well to exclude the color of Fe3+. Use a 20mm colorimetric dish and water as a reference to measure the absorbance of each tube at a wavelength of 665nm. Use hydrogen sulfide content (μg) as the horizontal axis and absorbance as the vertical axis to draw a standard curve, and calculate the slope of the regression line. The inverse of the slope is used as the calculation factor Bs (μg/absorbance) for sample determination. 6.1.2 Use standard gas to draw standard curve: Place hydrogen sulfide permeation tubes with known permeability at a constant temperature for more than 24 hours at the temperature of the calibrated permeability. Use pure nitrogen at a small flow rate (about 250mL/min) to take out the hydrogen sulfide gas that has permeated, and mix and dilute it with pure air. Adjust the air flow rate to obtain hydrogen sulfide standard gas of different concentrations. Use formula (2) to calculate the concentration of hydrogen sulfide standard gas. F1+F2
Where: ℃
Concentration of hydrogen sulfide standard gas under standard conditions, mg/m3, permeability of hydrogen sulfide permeation tube, μg/min, nitrogen flow rate under standard conditions, L/min,
(2)
Dilution air flow rate under standard conditions, L/min. F,
For example, if the permeability is 0.05μg/min, the nitrogen flow rate is 0.25L/min, and the air flow rate is 4.75L/min, then the hydrogen sulfide concentration is 0.01mg/m2. In this way, within the measurable concentration range (0.005-0.13 mg/m3), at least four concentration points of hydrogen sulfide standard gas are prepared, and zero concentration gas is used as reagent blank for determination. For standard gas at various concentration points, a certain volume of standard gas is collected according to the conventional sampling operating conditions (see Chapter 5). The sampling volume should be close to the volume of the air sample expected to be collected on site (e.g. sampling flow rate 1.0 L/min, gas volume 30 L). Then, the sample solution at each concentration point is filled with water to the volume of the absorption liquid before sampling, and the color is developed according to the operating steps of drawing a standard curve with a standard solution (see 6.1.1), and the absorbance of the sample solution at each concentration point is measured. With the concentration of hydrogen sulfide standard gas (mg/m3) as the horizontal axis and the absorbance as the vertical axis, a standard curve is drawn, and the slope of the regression line is calculated. The reciprocal of the slope is used as the calculation factor B [mg/(m3. Absorbance)] for sample determination. 6.2 Sample determination
After sampling, water is added to the volume of the absorption liquid before sampling. Since the sample solution is unstable, it should be colored within 6 hours according to the operating steps of drawing a standard curve with a standard solution (see 6.1.1) and the absorbance should be measured. At the same time as each batch of samples is measured, 10mL of unsampled absorption solution is used to measure the reagent blank color. If the absorbance of the sample solution exceeds the range of the standard curve, the sample solution can be diluted with the absorption solution before analysis. When calculating the concentration, the dilution multiple of the sample solution should be taken into account. 158
7 Result calculation
GB 11742+89
7.1 Use formula (3) to convert the sampling volume into the sampling volume under standard conditions. px
Vo=Vtx-
Where: V.
-sampling volume under standard conditions, L
V, sampling volume, obtained by multiplying the gas flow rate by the sampling time, L, To-
absolute temperature under standard conditions, 273K,
-atmospheric pressure under standard conditions, 101.3kPa; po-
atmospheric pressure at the time of sampling, kPa,
air temperature at the time of sampling, °C.
7.2 Calculation of hydrogen sulfide concentration in air
7.2.1 When the standard solution is used to prepare the standard curve, the hydrogen sulfide concentration in the air is calculated using formula (4). c
Where:
(A- Ao) ×Bs
Concentration of hydrogen sulfide in air, mg/m3,
Absorbance of sample solution;
Absorbance of reagent blank;
Calculation factor obtained from 6.1.1, μg/absorbance, dilution factor of sample solution during analysis.
When preparing the standard curve with standard gas, the concentration of hydrogen sulfide in air is calculated using formula (5). c=(A-Ao) ×Bg×D
Where: Bg—Calculation factor obtained from 6.1.2, mg/(m2.absorbance), other symbols are the same as formula (4).
8 Precision and accuracy
(3)
(4)
8.1 Reproducibility of the method: When the standard solution is used to prepare the standard curve, the average coefficient of variation of repeated measurements at each concentration point is 6%, and the average slope is within the confidence range of 0.155±0.010 absorbance/μg at a probability of 95%. The coefficient of variation of repeated measurements of the permeability of hydrogen sulfide permeation tubes by this method is 2%.
8.2 Accuracy of the method: The flow error does not exceed 5%. The permeability of hydrogen sulfide permeation tubes determined by this method is 96% on average compared with the value measured by the gravimetric method (the uncertainty of the gravimetric method is 2%). 159
A1 Reagent preparation
GB 11742 ---89
Appendix A
Preparation and concentration calibration method of sodium thiosulfate standard solution (supplement)
A1.10.1000N potassium iodate standard solution: accurately weigh 3.5668g potassium iodate (first grade) dried at 105℃ for 2h, dissolve it in water, transfer it to a 1L volumetric flask, add water to dilute to the scale, and shake well. A1.20.1N sodium thiosulfate standard solution: weigh 25g sodium thiosulfate (NaS2O3·5HO) and dissolve it in freshly boiled and cooled water, add 0.2g sodium carbonate, and dilute to 1L, store in a brown bottle, filter if turbid. After one week, calibrate the concentration. A2 concentration calibration method
Accurately measure 25.00mL 0.1000N potassium iodate standard solution, add 75mL freshly boiled and cooled water, add 3g potassium iodide and 10mL glacial acetic acid to a 250mL iodine volumetric flask. After shaking, place in a dark place for 3min, and titrate the precipitated iodine with 0.1N sodium thiosulfate standard solution until it turns light yellow. Add 1mL 0.5% starch solution, which turns blue. Continue to titrate until the blue color just fades away, which is the end point. Record the volume of sodium thiosulfate solution used. Repeat the titration twice, and the error of the volume of sodium thiosulfate solution used should not exceed 0.05mL. The concentration of sodium thiosulfate standard solution is calculated using formula (A1): N=0.1000×25.00
Where: N-
The equivalent concentration of sodium thiosulfate standard solution, V-The volume of sodium thiosulfate solution used for titration, mL. Additional Notes:
This standard was proposed by the Health Supervision Department of the Ministry of Health. This standard was drafted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine and the Wuhan Municipal Health and Epidemic Prevention Station. The main drafters of this standard were Cui Jiusi and Wang Hanping. This standard was interpreted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health. 1600L/min, gas volume 30L). Then, the sample solution at each concentration point is supplemented with water to the volume of the absorption solution before sampling, and the color is developed according to the operating steps of drawing a standard curve with a standard solution (see 6.1.1), and the absorbance of the sample solution at each concentration point is measured. With the concentration of hydrogen sulfide standard gas (mg/m3) as the horizontal axis and the absorbance as the vertical axis, a standard curve is drawn, and the slope of the regression line is calculated. The reciprocal of the slope is used as the calculation factor B [mg/(m3. Absorbance)] for sample determination. 6.2 Sample determination
After sampling, water is added to the volume of the absorption solution before sampling. Since the sample solution is unstable, it should be colored according to the operating steps of drawing a standard curve with a standard solution within 6 hours (see 6.1.1), and the absorbance should be measured. At the same time as each batch of samples is measured, 10mL of unsampled absorption solution is used to measure the reagent blank color. If the absorbance of the sample solution exceeds the range of the standard curve, the sample solution can be diluted with the absorption solution and then analyzed. When calculating the concentration, the dilution multiple of the sample solution should be taken into account. 158
7 Result calculation
GB 11742+89
7.1 Use formula (3) to convert the sampling volume into the sampling volume under standard conditions. px
Vo=Vtx-
Wherein: V.
-Sampling volume under standard conditions, L
V, sampling volume, obtained by multiplying the gas flow rate by the sampling time, L, To-
Absolute temperature under standard conditions, 273K,
-Atmospheric pressure under standard conditions, 101.3kPa; po-
Atmospheric pressure at the time of sampling, kPa,
Air temperature at the time of sampling, ℃.
7.2 Calculation of hydrogen sulfide concentration in air
7.2.1 When the standard solution is used to prepare the standard curve, the hydrogen sulfide concentration in the air is calculated using formula (4). c
Where:
(A- Ao) ×Bs
Concentration of hydrogen sulfide in air, mg/m3,
Absorbance of sample solution;
Absorbance of reagent blank;
Calculation factor obtained from 6.1.1, μg/absorbance, dilution factor of sample solution during analysis.
When preparing the standard curve with standard gas, the concentration of hydrogen sulfide in air is calculated using formula (5). c=(A-Ao) ×Bg×D
Where: Bg—Calculation factor obtained from 6.1.2, mg/(m2.absorbance), other symbols are the same as formula (4).
8 Precision and accuracy
(3)
(4)
8.1 Reproducibility of the method: When the standard solution is used to prepare the standard curve, the average coefficient of variation of repeated measurements at each concentration point is 6%, and the average slope is within the confidence range of 0.155±0.010 absorbance/μg at a probability of 95%. The coefficient of variation of repeated measurements of the permeability of hydrogen sulfide permeation tubes by this method is 2%.
8.2 Accuracy of the method: The flow error does not exceed 5%. The permeability of hydrogen sulfide permeation tubes determined by this method is 96% on average compared with the value measured by the gravimetric method (the uncertainty of the gravimetric method is 2%). 159
A1 Reagent preparation
GB 11742 ---89
Appendix A
Preparation and concentration calibration method of sodium thiosulfate standard solution (supplement)
A1.10.1000N potassium iodate standard solution: accurately weigh 3.5668g potassium iodate (first grade) dried at 105℃ for 2h, dissolve it in water, transfer it to a 1L volumetric flask, add water to dilute to the scale, and shake well. A1.20.1N sodium thiosulfate standard solution: weigh 25g sodium thiosulfate (NaS2O3·5HO) and dissolve it in freshly boiled and cooled water, add 0.2g sodium carbonate, and dilute to 1L, store in a brown bottle, filter if turbid. After one week, calibrate the concentration. A2 concentration calibration method
Accurately measure 25.00mL 0.1000N potassium iodate standard solution, add 75mL freshly boiled and cooled water, add 3g potassium iodide and 10mL glacial acetic acid to a 250mL iodine volumetric flask. After shaking, place in a dark place for 3min, and titrate the precipitated iodine with 0.1N sodium thiosulfate standard solution until it turns light yellow. Add 1mL 0.5% starch solution, which turns blue. Continue to titrate until the blue color just fades away, which is the end point. Record the volume of sodium thiosulfate solution used. Repeat the titration twice, and the error of the volume of sodium thiosulfate solution used should not exceed 0.05mL. The concentration of sodium thiosulfate standard solution is calculated using formula (A1): N=0.1000×25.00
Where: N-
The equivalent concentration of sodium thiosulfate standard solution, V-The volume of sodium thiosulfate solution used for titration, mL. Additional Notes:
This standard was proposed by the Health Supervision Department of the Ministry of Health. This standard was drafted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine and the Wuhan Municipal Health and Epidemic Prevention Station. The main drafters of this standard were Cui Jiusi and Wang Hanping. This standard was interpreted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health. 1600L/min, gas volume 30L). Then, the sample solution at each concentration point is supplemented with water to the volume of the absorption solution before sampling, and the color is developed according to the operating steps of drawing a standard curve with a standard solution (see 6.1.1), and the absorbance of the sample solution at each concentration point is measured. With the concentration of hydrogen sulfide standard gas (mg/m3) as the horizontal axis and the absorbance as the vertical axis, a standard curve is drawn, and the slope of the regression line is calculated. The reciprocal of the slope is used as the calculation factor B [mg/(m3. Absorbance)] for sample determination. 6.2 Sample determination
After sampling, water is added to the volume of the absorption solution before sampling. Since the sample solution is unstable, it should be colored according to the operating steps of drawing a standard curve with a standard solution within 6 hours (see 6.1.1), and the absorbance should be measured. At the same time as each batch of samples is measured, 10mL of unsampled absorption solution is used to measure the reagent blank color. If the absorbance of the sample solution exceeds the range of the standard curve, the sample solution can be diluted with the absorption solution and then analyzed. When calculating the concentration, the dilution multiple of the sample solution should be taken into account. 158
7 Result calculation
GB 11742+89
7.1 Use formula (3) to convert the sampling volume into the sampling volume under standard conditions. px
Vo=Vtx-bzxZ.net
Wherein: V.
-Sampling volume under standard conditions, L
V, sampling volume, obtained by multiplying the gas flow rate by the sampling time, L, To-
Absolute temperature under standard conditions, 273K,
-Atmospheric pressure under standard conditions, 101.3kPa; po-
Atmospheric pressure at the time of sampling, kPa,
Air temperature at the time of sampling, ℃.
7.2 Calculation of hydrogen sulfide concentration in air
7.2.1 When the standard solution is used to prepare the standard curve, the hydrogen sulfide concentration in the air is calculated using formula (4). c
Where:
(A- Ao) ×Bs
Concentration of hydrogen sulfide in air, mg/m3,
Absorbance of sample solution;
Absorbance of reagent blank;
Calculation factor obtained from 6.1.1, μg/absorbance, dilution factor of sample solution during analysis.
When preparing the standard curve with standard gas, the concentration of hydrogen sulfide in air is calculated using formula (5). c=(A-Ao) ×Bg×D
Where: Bg—Calculation factor obtained from 6.1.2, mg/(m2.absorbance), other symbols are the same as formula (4).
8 Precision and accuracy
(3)
(4)
8.1 Reproducibility of the method: When the standard solution is used to prepare the standard curve, the average coefficient of variation of repeated measurements at each concentration point is 6%, and the average slope is within the confidence range of 0.155±0.010 absorbance/μg at a probability of 95%. The coefficient of variation of repeated measurements of the permeability of hydrogen sulfide permeation tubes by this method is 2%.
8.2 Accuracy of the method: The flow error does not exceed 5%. The permeability of hydrogen sulfide permeation tubes determined by this method is 96% on average compared with the value measured by the gravimetric method (the uncertainty of the gravimetric method is 2%). 159
A1 Reagent preparation
GB 11742 ---89
Appendix A
Preparation and concentration calibration method of sodium thiosulfate standard solution (supplement)
A1.10.1000N potassium iodate standard solution: accurately weigh 3.5668g potassium iodate (first grade) dried at 105℃ for 2h, dissolve it in water, transfer it to a 1L volumetric flask, add water to dilute to the scale, and shake well. A1.20.1N sodium thiosulfate standard solution: weigh 25g sodium thiosulfate (NaS2O3·5HO) and dissolve it in freshly boiled and cooled water, add 0.2g sodium carbonate, and dilute to 1L, store in a brown bottle, filter if turbid. After one week, calibrate the concentration. A2 concentration calibration method
Accurately measure 25.00mL 0.1000N potassium iodate standard solution, add 75mL freshly boiled and cooled water, add 3g potassium iodide and 10mL glacial acetic acid to a 250mL iodine volumetric flask. After shaking, place in a dark place for 3min, and titrate the precipitated iodine with 0.1N sodium thiosulfate standard solution until it turns light yellow. Add 1mL 0.5% starch solution, which turns blue. Continue to titrate until the blue color just fades away, which is the end point. Record the volume of sodium thiosulfate solution used. Repeat the titration twice, and the error of the volume of sodium thiosulfate solution used should not exceed 0.05mL. The concentration of sodium thiosulfate standard solution is calculated using formula (A1): N=0.1000×25.00
Where: N-
The equivalent concentration of sodium thiosulfate standard solution, V-The volume of sodium thiosulfate solution used for titration, mL. Additional Notes:
This standard was proposed by the Health Supervision Department of the Ministry of Health. This standard was drafted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine and the Wuhan Municipal Health and Epidemic Prevention Station. The main drafters of this standard were Cui Jiusi and Wang Hanping. This standard was interpreted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health. 1601000N potassium iodate standard solution, add 75mL of freshly boiled and cooled water in a 250mL iodine volumetric flask, then add 3g potassium iodide and 10mL glacial acetic acid. After shaking, place in a dark place for 3min, and titrate the precipitated iodine with 0.1N sodium thiosulfate standard solution until it turns light yellow. Add 1mL of 0.5% starch solution, which turns blue. Continue titrating until the blue just fades away, which is the end point. Record the volume of sodium thiosulfate solution used. Repeat the titration twice, and the error of the volume of sodium thiosulfate solution used should not exceed 0.05mL. The concentration of sodium thiosulfate standard solution is calculated using formula (A1): N=0.1000×25.00
Where: N-
The equivalent concentration of sodium thiosulfate standard solution, V—The volume of sodium thiosulfate solution used for titration, mL. Additional remarks:
This standard is proposed by the Health Supervision Department of the Ministry of Health. This standard was drafted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine and the Wuhan Municipal Health and Epidemic Prevention Station. The main drafters of this standard are Cui Jiusi and Wang Hanping. This standard is interpreted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health.1000N potassium iodate standard solution, add 75mL of freshly boiled and cooled water in a 250mL iodine volumetric flask, then add 3g potassium iodide and 10mL glacial acetic acid. After shaking, place in a dark place for 3min, and titrate the precipitated iodine with 0.1N sodium thiosulfate standard solution until it turns light yellow. Add 1mL of 0.5% starch solution, which turns blue. Continue titrating until the blue just fades away, which is the end point. Record the volume of sodium thiosulfate solution used. Repeat the titration twice, and the error of the volume of sodium thiosulfate solution used should not exceed 0.05mL. The concentration of sodium thiosulfate standard solution is calculated using formula (A1): N=0.1000×25.00
Where: N-
The equivalent concentration of sodium thiosulfate standard solution, V—The volume of sodium thiosulfate solution used for titration, mL. Additional remarks:
This standard is proposed by the Health Supervision Department of the Ministry of Health. This standard was drafted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine and the Wuhan Municipal Health and Epidemic Prevention Station. The main drafters of this standard are Cui Jiusi and Wang Hanping. This standard is interpreted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health.
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