This standard specifies the determination of chlorine concentration in residential atmosphere by methyl orange spectrophotometry. This standard applies to the determination of chlorine concentration in residential atmosphere. GB/T 11736-1989 Standard method for the determination of chlorine in residential atmosphere Methyl orange spectrophotometry GB/T11736-1989 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Standard method for hygienic examination ofchlorine in air of residential areas-Methylorange spectrophotometric method
Standard method for hygienic examination ofchlorine in air of residential areas-Methylorange spectrophotometric method1 Subject content and scope of application
This standard specifies the determination of chlorine concentration in the atmosphere of residential areas by methyl orange spectrophotometric method. This standard is applicable to the determination of chlorine concentration in the atmosphere of residential areas. GB 11736--89
1.1 Sensitivity
The absorbance of 2μg chlorine in the final color development volume of 10mL should be at least 0.12 less than the absorbance of the zero tube. 1.2 Lower limit of detection
The lower limit of detection is 0.4μg. If the sampling volume is 20L, the minimum detection concentration is 0.02mg/m3. 1.3 Determination range
The linear range of this method is 0.4~8.0μg/10mL. If the sampling volume is 20L, the measurable concentration range is 0.02~0.4mg/m2. 1.4 Interference
Hydrochloric acid gas and chloride do not interfere with the determination. Oxidizing and reducing gases in the atmosphere will interfere, such as free bromine and chlorine have the same reaction, producing positive interference. Sulfur dioxide has negative interference in the chlorine absorption solution, nitrogen dioxide produces positive interference, and hydrogen sulfide produces negative interference. Therefore, when measuring on site, special attention should be paid to the influence of these interfering substances. 2 Principle
In an acidic solution, chlorine displaces bromine when it meets potassium bromide, and bromine can oxidize methyl orange and make it fade. Colorimetric quantification is based on the degree of color reduction. bzxz.net
3 Reagents and Materials
All reagents used in this method are analytically pure unless otherwise specified, and all water used is redistilled water or deionized water. 3.1 Absorption solution
3.1.1 Absorption solution: Accurately weigh 0.100g of methyl orange, dissolve in 50-100mL of 40-50℃ water, and cool to room temperature. Add 20mL of 95% ethanol, transfer to a 1L volumetric flask, and add water to the scale. Place in a dark place and it can be stored for half a year. 3.1.2 Absorption stock solution: Measure 50mL of stock solution, add 1g of potassium bromide to a 500mL volumetric flask, and dilute to the scale with water. Using water as a reference, use a 10mm colorimetric IIIl, and adjust with the stock solution and water at a wavelength of 460nm to prepare an absorption stock solution with an absorbance of 0.63. 3.1.3 Absorption working solution: Before sampling, measure 250mL absorption stock solution and 50mL 1+6 sulfuric acid solution, put them in a 500mL volumetric flask, and dilute to the mark with water. Mix well to make absorption working solution. Prepare immediately before use. 3.2 1+6 sulfuric acid solution: Measure 30mL concentrated sulfuric acid and slowly add it to 180mL water. 3.3 Chlorine standard solution
3.3.1 Standard preparation solution: Accurately weigh 1.1776g potassium bromate (super pure) dried at 105C for 2h. Dissolve it with a small amount of water, transfer it to a 500mL volumetric flask, and dilute to the mark with water. Accurately pipette 10.00mL into a 1L volumetric flask, add water to the mark, this solution 1.00mL contains 30μg chlorine. Store in a dark place and it can be stored for half a year. 3.3.2 Standard application solution: When using, dilute the stock solution with water to 1.00mL of standard application solution containing 5μg chlorine. 4 Instruments and equipment
4.1 Porous glass plate absorption tube (see the figure below): Fill with 10mL absorption solution. At a flow rate of 0.5L/min, the filter plate resistance of the absorption tube should be 4-5.3kPa, and the bubbles after passing through the filter plate should be evenly dispersed. O1
Glass filter plate
Porous glass plate absorption tube (thickness 1～1.2mm)4.2Empty sampler: flow range 0.2～1L/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%. 4.3Colorimetric tube with stopper: 10mL.
4.4Spectrophotometer: Use 10mm colorimetric tube to measure absorbance at a wavelength of 505nm. 5Sampling
Use a porous glass plate absorption tube with 10mL absorption liquid inside to collect gas at a flow rate of 0.5L/min. When the color of the absorption liquid fades significantly, stop sampling. If it does not fade, the sampling should be no less than 20L. And record the temperature and atmospheric pressure during sampling. 6 Analysis steps
6.1 Drawing of standard curve
6.1.1 Use 8 10mL stoppered colorimetric tubes to prepare standard colorimetric tubes according to the following table. 505
Standard application solution, mL
Water, ml
Chlorine content, μg
GB1173689
Standard colorimetric tubes
Add 5mL absorption stock solution and 1mL 1+6 sulfuric acid solution to each tube. 3
6.1.2 Gently invert each tube of the standard series to mix. At 35℃, after 20min (low temperature can prolong the color development time and the color can be stable for 50h), use 10mm colorimetric III to measure the absorbance at a wavelength of 505nm with water as reference. Use the difference between the absorbance of the zero standard tube and each tube as the ordinate and the chlorine content (μg) as the abscissa to draw a standard curve, or calculate the slope of the regression line, and use the reciprocal of the slope as the sample determination factor Bs (μg/absorbance). 6.2 Sample determination
After sampling, transfer all the sample solution into the colorimetric tube, wash the absorption tube with a small amount of water, and combine them to make the total volume 10mL. Then operate according to the method in 6.1.2 to determine the absorbance. At the same time, take another unsampled absorption liquid and perform zero tube absorbance determination. Result calculation
7.1 Convert the sampling volume into the sampling volume under standard conditions according to formula (1). V=V+×
-sampling volume under standard conditions, L,
-sampling volume, obtained by multiplying the sampling flow rate by the sampling time, L, T-absolute temperature under standard conditions, 273K,-air temperature at the time of sampling, °C,
po-atmospheric pressure under standard conditions, 101.3kPap
maximum pressure at the time of sampling, kPa.
Air chlorine concentration is calculated according to formula (2).
(Ao - A) × Bs
Wuzhong:-air chlorine concentration, mg/m\;
A-absorbance of standard tube solution;
A-absorbance of crystal tube solution;
Bs-calculation factor obtained from 6.1, μg/absorbance. Precision and accuracy
(2)
When the chlorine content is within the range of 1-8μg/10mL, the average coefficient of variation is 6%. When the chlorine content is within the range of 3-6μg/10mL, the yield of the sample plus standard is 93-110%.
Additional remarks:
This standard was proposed by the Health Supervision Department of the Ministry of Health. GB1173689
This standard was drafted by the Environmental Health Monitoring Station of Shandong Province, the Health and Epidemic Prevention Station of Shexian County, Anhui Province, and the Health and Epidemic Prevention Station of Wuhan City. The main drafters of this standard are Liu Beijin and Chen Jicheng. This standard was issued by the Institute of Environmental Health Monitoring, Chinese Academy of Preventive Medicine, a technical export unit entrusted by the Ministry of Health. 507
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