GB/T 15435-1995 Determination of nitrogen dioxide in ambient air - Saltzman method
Some standard content:
National Standard of the People's Republic of China
Determination of nitrogen dioxide in ambient air
Saltzman method
Ambient air--Determination of nitrogendioxideSaltzman method
1 Subject content and scope of application
1.1 Subject content
This standard specifies the spectrophotometric method for determining nitrogen dioxide in ambient air. 1.2 Scope of application
GB/T15435--1995
When the sampling volume is 4 to 24L, this standard is applicable to the determination of nitrogen dioxide in the air with a concentration range of 0.015 to 2.0mg/m3. 2 Reference Standards
GB5275 Preparation of Mixed Gas for Gas Analysis Calibration Permeation Method 3 Terminology
Saltzman Experimental Coefficient (f): The ratio of the amount of azo dye equivalent to nitrite generated by the absorption liquid in the gas sampling process of the nitrogen dioxide calibration mixed gas prepared by the permeation method to the total amount of nitrogen dioxide passing through the sampling system. This coefficient is the average value of repeated experiments. The determination method is shown in Appendix B. 4 Principle
Nitrogen dioxide in the air undergoes a diazotization reaction with p-aminobenzenesulfonic acid in the absorption liquid, and then reacts with N-(1-amino)ethylenediamine hydrochloride to generate a pink azo dye. The absorbance is measured at a wavelength between 540 and 545 nm. 5 Reagents
Unless otherwise specified, analytical reagents that meet national standards and distilled water without nitrite or water of equivalent purity are used during analysis. If necessary, a small amount of potassium permanganate and barium hydroxide can be added to the all-glass distiller for redistillation. Test method for water purity: Measure according to 8.1.1. The absorbance of the absorption solution shall not exceed 0.005. 5.1 N-(1-naphthyl)ethylenediamine hydrochloride stock solution: Weigh 0.50g N-(1-naphthyl)ethylenediamine hydrochloride [CiH, NH(CH2), NH2·2HCII in a 500mL volumetric flask, dissolve and dilute to the mark with water. This solution is stored in a sealed brown reagent bottle and refrigerated in a refrigerator. It can be stable for three months.
5.2 Color development solution: Weigh 5.0g p-nitrobenzenesulfonic acid [NH.CH.SO.H, dissolve in about 200mL hot water, cool the solution to room temperature, transfer all of it to a 1000mL volumetric flask, add 50mL glacial acetic acid and 50.0ml. N-(1-yl)ethylenediamine hydrochloride stock solution (5.1), and dilute to the mark with water. This solution is stored in a sealed brown bottle in a dark place below 25°C and can be stable for three months. 5.3 Absorption solution: When using, mix the color developing solution (5.2) and water in a ratio of 4+1 (V/V) to obtain the absorption solution. This solution is stored in a sealed brown bottle in a dark place below 25°C and is stable for three months. If it turns light red, it should be re-prepared. Approved by the State Environmental Protection Agency on March 25, 1995, and implemented on August 1, 1995
GB/T 15435---1995
5.4 Nitrite standard stock solution: 250mgNOz/L. Accurately weigh 0.3750g sodium nitrite (NaNO2, high-grade pure, placed in a desiccator for 24h in advance), transfer it to a 1000mL volumetric flask, and dilute it to the mark with water. This solution is stored in a sealed bottle in a dark place and is stable for three months.
5.5 Nitrite standard working solution: 2.50mgNOz/L. Dilute with nitrite standard stock solution (5.4). Prepare immediately before use. 5.6 Calibration gas mixture: When in use, prepare zero gas and at least four concentrations of nitrogen dioxide calibration gas mixtures that can cover the desired measurement range according to the permeation method specified in GB5275.
6 Instruments
6.1 Sampling probe: borosilicate glass, stainless steel, polytetrafluoroethylene or silicone tube, inner diameter of about 6mm, as short as possible, no longer than 2m in any case, equipped with a downward air inlet. 6.2 Absorption bottle: porous glass plate absorption bottle containing 10mL, 25mL or 50mL absorption liquid, with a liquid column of not less than 80mm. Check the glass plate resistance of the absorption bottle, the uniformity of bubble dispersion and the sampling efficiency according to Appendix A. The following figure shows two more suitable porous glass plate absorption bottles. 50mL
Schematic diagram of porous glass plate absorption bottle
6.3 Air sampler:
6.3.1 Portable air sampler: flow range 0～1L/min. When the gas flow rate is 0.4L/min, the error is less than ±5%.6.3.2 Constant temperature automatic continuous sampler: When the gas flow rate is 0.2L/min, the error is less than ±5%. It can keep the absorption liquid temperature at 20±4℃.
6.4 Spectrophotometer.
6.5 Silicone tube: inner diameter is about 6mm.
7 Sample
7.1 Short-time sampling (within 1h): Take a porous glass plate absorption bottle, fill it with 10.0mL absorption liquid (5.3), mark the absorption liquid level position, and collect 6～24L of gas at a flow rate of 0.4L/min. 7.2 Long-term sampling (within 24h): Use a large porous glass plate absorption bottle, filled with 25.0mL or 50.0mL absorption liquid, the liquid column is not less than 80mm, mark the position of the absorption liquid surface, keep the absorption liquid temperature at 204℃, and collect 288L of gas at a flow rate of 0.2L/min from 9:00 to 9:00 the next day.
Avoid sunlight during sampling, transportation and storage of samples. When the temperature exceeds 25℃, cooling measures should be taken for long-term transportation and storage of samples. 7.3 Interference and elimination
GB/T 15435-1995
When the ozone concentration in the air exceeds 0.25mg/m2, the absorption liquid will appear slightly red, which will have negative interference with the determination of nitrogen dioxide. When sampling, connect a 15-20cm long silicone tube in series at the inlet of the absorption bottle to reduce the ozone concentration to a level that does not interfere with the determination of nitrogen dioxide. 8 Analysis stepswww.bzxz.net
8.1 Drawing of calibration curve
8.1.1 Drawing of standard curve with nitrite standard solution Take 6 10mL stoppered colorimetric tubes and prepare standard color series according to Table 1: Table 1 Nitrite standard color series
Standard working solution (5.5), mL
Water, mL
Color developing solution (5.2), mL
NO, concentration, μg/mL
Mix each tube and place it in a dark place for 20 minutes (when the room temperature is below 20℃, the color development time should be appropriately extended. For example, when the room temperature is 15℃, the color development time is 40 minutes). Use 10mm colorimetric blood and water as reference to measure the absorbance at a wavelength between 540 and 545nm. After deducting the absorbance of the blank test (zero concentration), the corresponding NOz concentration (μg/mL) is calculated using the least squares method to calculate the regression equation of the standard curve. 8.1.2 Plotting the working curve with nitrogen dioxide standard gas According to the method specified in GB5275, prepare zero gas and nitrogen dioxide standard mixed gas of at least four concentrations that can cover the concentration range to be measured. Sample gas according to the sampling operation conditions (see Chapter 7). The sampling volume should be close to the volume of air samples expected to be collected on site. Measure the absorbance according to 8.1.1. Take the ratio of the nitrogen dioxide content (μg) in the standard mixed gas passing through the sampling system to the volume of the absorption liquid in the sampling bottle (mL) as the horizontal axis; take the difference between the absorbance of the sample solution at each concentration point (A) and the absorbance of the sample solution at the zero concentration point (A.) as the vertical axis, and plot the working curve.
8.2 Sample determination
After sampling, place it for 20 minutes (when the temperature is low, appropriately extend the color development time. For example, at 15℃, the color development time is 40 minutes), fill the volume of the absorption liquid in the sampling bottle to the mark with water, mix well, and measure the absorbance of the sample and the absorbance of the blank test sample according to 8.1.1. If the absorbance of the sample exceeds the upper limit of the calibration curve, it should be diluted with blank test solution and then its absorbance should be measured. The absorbance of the sample should be measured as soon as possible after sampling. If it cannot be analyzed in time, the sample should be stored in a low temperature dark place. The sample can be stable for 8 hours when stored in a dark place at 30℃; it can be stable for 24 hours when stored in a dark place at 20℃; it can be stable for at least three days when refrigerated at 0-4℃. 8.3 Blank test
The absorption solution prepared in the same batch as the absorption solution used for sampling. 9 Expression of results
9.1 When the standard curve is drawn with the nitrite standard solution, the concentration of nitrogen dioxide in the air Cno, (mg/m2) is calculated using formula (1): CNO
Where: A——absorbance of sample solution; A.——absorbance of blank test solution; 6-
(AA.-a) × V × D
bxfxV.
The slope of the standard curve measured according to 8.1.1, absorbance·mL/μg; a--The intercept of the standard curve measured according to 8.1.1; V
The volume of the absorption liquid used for sampling, mL;
（1）
GB/T 15435--1995
-Converted to standard state (273K, 101.3kPa), L; V.
D dilution factor of the sample;
-Saltzman experimental coefficient, 0.88 (when the concentration of nitrogen dioxide in the air is higher than 0.720mg/m, the f value is 0.77). f
9.2 When the working curve is drawn with nitrogen dioxide standard gas, the concentration of nitrogen dioxide in the air Cno. (mg/m2) is calculated by formula (2): CNo,
CxV×D
Where: C——NO2 concentration found on the working curve measured in 8.1.2, μg/mL; V—volume of absorption liquid for sampling, mL;
V. Converted to the sampling volume under standard conditions (273K, 101.3kPa), L; D-—dilution factor of the sample.
10 Density and accuracy
Precision and accuracy of nitrite standard solution 10.1
Table 2 Precision and accuracy data
NO, concentration
μg/mL
0. 715±0. 03
0.358±0.01
0.072±0.00
Analysis results
Precision, μg/mL
·（2）
Accuracy
(m -C) /C
The precision and accuracy data were determined in 1993 by six laboratories on samples of three concentration levels, with six repeated measurements and a probability level of 95%.
10.2 Determination of precision and accuracy of NO2 standard gas Five laboratories measured NO2 standard gas with a concentration range of 0.056~～0.480mg/m2, and the repeatability coefficient of variation was less than 10%, and the relative error was less than ±8%.
A1 Inspection of glass plate resistance and micropore uniformity
GB/T 15435—1995
Appendix A
Inspection of absorption bottle
(Supplement)
Before using a new porous glass plate absorption bottle, soak it in (1+1) HC1 for more than 24 hours and wash it with clean water. Before using each absorption bottle or after using it for a period of time, the glass plate resistance should be measured to check the uniformity of bubble dispersion after passing through the glass plate. Absorption bottles with resistance that does not meet the requirements and uneven bubble dispersion should not be used.
When sampling at a flow rate of 0.4L/min for a porous glass plate absorption bottle containing 10mL of absorption liquid, the resistance of the glass plate is 4~5kPa, and the bubbles passing through the glass plate should be evenly dispersed.
When sampling at a flow rate of 0.2L/min for a large porous glass plate absorption bottle containing 50mL of absorption liquid, the resistance of the glass plate is 5~6kPa. The bubbles passing through the glass plate should be evenly dispersed.
A2 Determination of sampling efficiency
The sampling efficiency of the absorption bottle should be measured before use and after a period of use. Connect two absorption bottles in series and operate according to Section 7.1 to collect ambient air. When the concentration of NO in the first absorption bottle is about 0.4μg/mL, stop sampling. Measure the absorbance of the samples in the two absorption bottles before and after according to 8.1.1, and calculate the sampling efficiency (E) of the first absorption bottle according to formula (A1): C
Wherein: C, and C2 are the concentrations of NO, in the first and second absorption bottles connected in series, ug/mL. Note: Absorption bottles with sampling efficiency E lower than 0.97 should not be used. Appendix B
Determination of Saltzman Experimental Coefficient
(Supplement)
Prepare zero gas and nitrogen dioxide standard mixed gas of the concentration range to be measured according to the method specified in GB5275. Collect gas samples according to 7.1, and stop sampling when the NOz concentration in the absorption liquid reaches about 0.4ug/mL. Operate according to 8.1.1 and measure the absorbance of the sample. Calculate the Saltzman experimental coefficient (f) according to formula Bl: f= (A_A_a)×y
bx V. × Cno2
Where: A——absorbance of sample solution; A. -absorbance of blank test (zero concentration) sample; b, a～slope (absorbance·mL/μg) and intercept of standard curve measured according to 8.1.1; V-—volume of absorption liquid for sampling, mL;
V. ——sampling volume converted to standard push state (101.3kPa, 273K), L; Cno concentration of NO2 standard mixed gas passing through sampling system, mg/m (101.3kPa, 273K). (B1)
GB/T15435--1995
The size of f value is affected by factors such as NO2 concentration in air, sampling flow rate, absorption bottle type, sampling efficiency, etc. Therefore, when measuring f value, the measuring conditions should be kept consistent with the actual sampling as much as possible. Additional remarks:
This standard is proposed by the Science and Technology Standard Division of the State Environmental Protection Administration. This standard was drafted by Shenyang Environmental Monitoring Center. The main drafters of this standard are Wang Yuping, Chen Tao, Du Pingping, Wang Juan and Liu Congrong. 21.01. Measure the absorbance of the sample. Calculate the Saltzman experimental coefficient (f) according to formula Bl: f = (A_A_a) × y
bx V. × Cno2
Wherein: A——absorbance of sample solution; A. - absorbance of blank test (zero concentration) sample; b, a～slope (absorbance·mL/μg) and intercept of the standard curve measured according to 8.1.1; V-—volume of absorption liquid for sampling, mL;
V. ——sampling volume converted to standard push state (101.3kPa, 273K), L; Cno is the concentration of NO2 standard mixed gas passing through the sampling system, mg/m (101.3kPa, 273K). (B1)
GB/T15435--1995
The f value is affected by factors such as the concentration of NO2 in the air, sampling flow, absorption bottle type, sampling efficiency, etc. Therefore, when measuring the f value, the measurement conditions should be kept consistent with the actual sampling conditions. Additional notes:
This standard was proposed by the Science and Technology Standards Department of the State Environmental Protection Administration. This standard was drafted by the Shenyang Environmental Monitoring Center. The main drafters of this standard are Wang Yuping, Chen Tao, Du Pingping, Wang Juan, and Liu Congrong. 21.01. Measure the absorbance of the sample. Calculate the Saltzman experimental coefficient (f) according to formula Bl: f = (A_A_a) × y
bx V. × Cno2
Wherein: A——absorbance of sample solution; A. - absorbance of blank test (zero concentration) sample; b, a～slope (absorbance·mL/μg) and intercept of the standard curve measured according to 8.1.1; V-—volume of absorption liquid for sampling, mL;
V. ——sampling volume converted to standard push state (101.3kPa, 273K), L; Cno is the concentration of NO2 standard mixed gas passing through the sampling system, mg/m (101.3kPa, 273K). (B1)
GB/T15435--1995
The f value is affected by factors such as the concentration of NO2 in the air, sampling flow, absorption bottle type, sampling efficiency, etc. Therefore, when measuring the f value, the measurement conditions should be kept consistent with the actual sampling conditions. Additional notes:
This standard was proposed by the Science and Technology Standards Department of the State Environmental Protection Administration. This standard was drafted by the Shenyang Environmental Monitoring Center. The main drafters of this standard are Wang Yuping, Chen Tao, Du Pingping, Wang Juan, and Liu Congrong. 21.0
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