GB/T 11731-1989 Standard method for the sanitary examination of nitrobenzene in the atmosphere of residential areas - Gas chromatography
Some standard content:
National Standard of the People's Republic of China
Standard method for hygienic examinationof nitrobenzene in air of residential areas ---Gas chromatography
1 Subject content and scope of application
This standard specifies the determination of nitrobenzene concentration in air of residential areas by gas chromatography. This standard is applicable to the determination of nitrobenzene concentration in the atmosphere of residential areas. GB 11731—89
1.1 Detection limit
The injection volume is 1μL, and the detection limit is 2×10-5μg. If the sampling volume is 20L, the minimum detection concentration is 0.002mg/m2.1.2 Measurement range
When the sampling volume is 20L, the measurement range is 0.002~0.1mg/m3.1.31 Interference and exclusion
Due to the use of chromatographic separation technology, common coexisting pollutants: nitrochlorobenzene, dinitrobenzene, dinitrobenzene and aniline are not interfered with the determination.
2 Principle
After nitrobenzene in the air is adsorbed by the silica gel tube, it is eluted by the desorption liquid, separated by the chromatographic column, and determined by the electron capture detector. The retention time is used for qualitative analysis and the peak height is used for quantitative analysis.
3 Reagents and Materials
The reagents used in this method are all analytically pure. Benzene must be tested before use to confirm that it does not contain nitrobenzene, otherwise it should be redistilled. Nitrobenzene standard is chromatographic pure.
3.1 Silica gel sampling tube
3.1.1 Silica gel pretreatment: Use 20-50 mesh coarse pore spherical silica gel, soak it in concentrated sulfuric acid overnight, carefully pour off the sulfuric acid, rinse it with tap water until it is transparent, soak and rinse it with distilled water 2-3 times, dry it in an oven, and then bake it at 360℃ in a high-temperature furnace for more than 4 hours. After cooling, place it in a desiccator for use.
3.1.2 Preparation of silica gel tube: Wash and dry a hard glass tube with a length of 20cm, an inner diameter of 6mm, and an outer diameter of 8mm, and fill it with 600mg and 200mg of treated silica gel in sections, separate it with about 15mg of glass wool in the middle, plug the two ends with about 15mg of glass wool respectively, and seal it with a blowtorch. 3.2 Desorption solution: 5% (V/V) methanol-benzene solution, stored in a refrigerator. 3.3 Standard solution: In a 25mL volumetric flask, add about 10mL of benzene, weigh accurately, add a small amount of nitrobenzene and weigh accurately again. The difference between the two weighings is the amount of nitrobenzene. Add benzene to the scale and mix well. Calculate the content of nitrobenzene in each milliliter of solution, divide it into glass bottles and store it. When using, dilute it with desorption solution to a standard solution of four concentration points of 0.05~0.50μg/mL. 4 Instruments and equipment
4.1 Gas chromatograph: with electron capture detector. Approved by the Ministry of Health of the People's Republic of China on September 21, 1989 and implemented on July 1, 1990
4.2 Chromatographic column:
GB 11731-89
2m long, 4mm inner diameter glass column, filled with ChromosorbWAWDMCS (60-80 mesh), coated with 2%OV-17 + 1.5%QF-1.
4.3 Air sampler: flow range 0.2-1Lmin. Stable flow. When in use, use a soap film meter to calibrate the flow of the sampling series before and after sampling. The flow error should be less than 5%. 4.4 Micro-syringe: 1μL, 5μL, the volume scale should be calibrated. 5 Sampling
Open both ends of the silicone tube, and the port diameter should be greater than 0.5 times the inner diameter of the glass tube. Connect the rear end of the silicone tube, i.e. the end with less silicone, vertically to the sampler, collect about 30L of gas at a flow rate of 0.5-1L/min, and immediately put on the plastic cap. Record the temperature and atmospheric pressure of the sampling point. The sample can be stored for one week at room temperature.
6 Analysis steps
Chromatographic analysis conditions
Chromatographic analysis conditions often vary due to different experimental conditions, so the best chromatographic analysis conditions for analyzing nitrobenzene should be formulated according to the model and performance of the gas chromatograph used. The chromatographic analysis conditions listed in Appendix A (reference) are an example. 6.2 Drawing the standard curve and determining the correction factor 6.2.1 Drawing the standard curve: Pipette 1.0μL of the standard solution at four concentration points of 0.05~0.50μg/mL, inject it into the chromatograph, and obtain the chromatographic peaks and retention times of each concentration. Each concentration was measured three times, with the average value of the peak height (mm) as the ordinate and the concentration (μg/mL) as the abscissa. A standard curve was drawn and the slope of the regression line was calculated. The reciprocal of the slope was used as the calculation factor Bs (μg/(mL·mm)) for sample determination.
6.2.2 Determination of correction factor
When the instrument has poor stability, the correction factor can be obtained by single-point correction. While the sample is being determined, 1.0μL of sample is injected to take zero concentration and a standard solution with a concentration close to that of nitrobenzene in the sample extract, respectively. According to 6.2.1, the chromatographic peak height (mm) and retention time of the zero concentration and the standard are measured. The correction factor is calculated using formula (1). f=
f--correction factor, μg/(mL·mm); where: wwW.bzxz.Net
ho, hs--average peak height of zero concentration and standard solution, mm; c.
6.3 Determination of standard product
-concentration of standard solution, μg/mL.
（1）
Pour the front and back sections of the sampled silicone tube into a stoppered test tube, add 2.0mL of desorption solution to the front section and 1.0mL of desorption solution to the back section. After standing for 30 minutes (shake twice during this period), remove the bubbles on the surface of the silica gel, take 1.0μL of the desorbed sample solution and operate according to 6.2.1 to obtain the half-mean value (mm) of the sample peak height.
When analyzing the sample, use an unsampled silicone tube to perform the reagent narrow white determination according to the sample determination steps. 7 Result calculation
7.1 Convert the sampling volume to the sampling volume under standard conditions according to formula (2). Vo=Vt ×
Where: V is the sampling volume converted to the standard condition, L, V is the sampling volume obtained by multiplying the sampling flow rate by the sampling time, L, T. ——absolute temperature under standard conditions, 273K, t——temperature at the sampling point during sampling, ℃,
GB 11731-89
atmospheric pressure under standard conditions, 101.3kPa, p
——atmospheric pressure at the sampling point during sampling, kPa. 7.2 Standard curve method Use formula (3) to calculate the concentration of nitrobenzene in the air. 7.2.1 Use calculation factor B. Calculation results. c
Where:
hi, ho
(h,-ho)·Bs.
Nitrobenzene concentration in air, mg/m3,
Average peak height of sample desorption solution and reagent blank desorption solution, mm, calculation factor obtained from 6.2.1, μg/(mL·mm)-converted to sampling volume under standard conditions, L, extraction efficiency determined by experiment;
A --sample desorption solution volume, mL1
A,--injection volume, mL.
7.3 Single-point calibration method Calculate the nitrobenzene concentration in air according to formula (4). c=
(hr-ho)·f
V. ·E
CNitrobenzene concentration in air, mg/m2,
Where:
h,,h. ——Average peak height of sample desorption solution and reagent blank desorption solution, mm, f-correction factor obtained by 6.2.2, μg/(mL·mm)V. Converted to sampling volume under standard conditions, L, E-extraction efficiency determined by experiment, 0.94, A-volume of sample desorption solution, mL,
A, injection volume, mL.
Precision and accuracy
·(3)
(4)
When the concentration of standard nitrobenzene added to the sample was 0.05, 0.10, and 0.25μg/mL, the average recovery rate was 94% and the combined coefficient of variation was 3.4%.
Column box temperature: 165℃,
Detection chamber temperature: 220℃,
Vaporization chamber temperature: 220℃,
GB 11731—89
Appendix A
Example of chromatographic conditions for the determination of nitrobenzene by gas chromatography (reference)
Carrier (high-purity nitrogen): 35mL/min,
Recorder: full scale 1mV, paper speed 8mm/min. Additional remarks:
This standard was proposed by the Department of Health Supervision of the Ministry of Health. This standard was drafted by the Nanjing Municipal Health and Epidemic Prevention Station, the Jiangsu Provincial Health and Epidemic Prevention Station, and the Yangzhou Municipal Health and Epidemic Prevention Station. The main drafters of this standard are Huang Fuxin, Cheng Yuhua, Wu Caigang, and Wang Qinyuan. This standard is interpreted by the Institute of Environmental Health Monitoring, Chinese Academy of Preventive Medicine, the technical unit entrusted by the Ministry of Health. 488
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