Standard method for hygienic inspection of chloroform and carbon tetrachloride in the atmosphere
Standard method for hygienic inspection of chloroform and carbon tetrachloride in the atmosphere (gas chromatography) 1 Subject content and scope of application This standard specifies the method for determining the concentration of chloroform and carbon tetrachloride in the atmosphere of residential areas by gas chromatography.
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This standard applies to the determination of the concentration of chloroform and carbon tetrachloride in the atmosphere of residential areas. It is also suitable for the determination of chloroform and carbon tetrachloride in the air of public places.
2 Principles Chloroform and carbon tetrachloride are completely separated from the coexistence program control substances in the chromatographic column, and then measured by an electron capture detector to be qualitative by retention time and quantified by peak height.
3 Reagents and materials
3.1 Chloroform: chromatographically pure.
Carbon tetrachloride: chromatographically pure.
1.1-Dichloroethane, trichloroethylene, tetrachloroethylene, dichloromethane: all are analytically pure.
3.2 Stationary phase: 5% SE-30 Chromosorb WAW-DMSC MHSH 60 ～ 80.
4 Instruments and equipment
4.1 Gas chromatograph: equipped with electron capture detector.
4.2 Chromatographic column: A glass column with a length of 2m and an internal diameter of 3mm, which contains a SE-30 stationary phase.
4.3 Gas recovery bag: plastic aluminum foil composite film gas recovery bag with a volume of 400mL.
4.4 Syringe: 100mL, 50mL, 1mL, 1μL, 10μL, 100μL.
4.5 Oven: 0 ～ 200 ℃.
The above equipment is pre-cleaned and injected into the gas chromatograph should be free of halogenated hydrocarbon peaks.
5 Use a syringe to sample the on-site air into the gas bag to make it full, and then let go. Repeat this for three times, and seal the inlet with a silicone rubber pad after it is full. Write a label indicating the time and place.
6 Analysis steps
6.1 Chromatographic analysis conditions are often different due to different experimental conditions, so the best chromatographic conditions for the analysis of chloroform and carbon tetrachloride should be formulated according to the type and performance of the gas chromatograph used (see Appendix A).
6.2 Drawing of standard curve and determination of correction factors
6.2.1 Preparation of standard gas
a. Take 0.34μL (d 20 ℃ / 4 ℃ 1.47) of chloroform into a 100mL syringe filled with nitrogen and a small aluminum foil, put it in an oven (70 ～ 80 ℃), mix and balance for 10min, and keep it stable After that, the standard gas concentration was 5 μg / mL.
b. Take 0.31μL (d 20 ℃ / 4 ℃ 1.62) carbon tetrachloride into the 100mL syringe by the same method, the standard gas concentration is 5μg / mL.
6.2.2 Draw standard curve Take 4 100mL syringes filled with nitrogen, add chloroform standard gas 0, 40, 80, 120μL (concentration is 0, 2, 4, 6μg / L) and carbon tetrachloride standard Gases 0, 10, 30, 50 μL (concentration 0, 0.5, 1.5, 2.5 μg / L). Repeat the measurement of the above standard gas at each concentration, take 10 μL into the gas chromatographic measurement, record the retention time qualitatively, and draw the standard curve with the average peak height or peak area and the concentration of chloroform and carbon tetrachloride.
6.2.3 Determination of the correction factor During the sample analysis, take chloroform and carbon tetrachloride standard gases that are close to the content in the sample, measure the retention time and average peak value according to 6.2.2 operation, and calculate according to formula (1) Correction factor:
¦ = c0 / h0 .................................... (1)
In the formula: ¦ ─ correction factor;
c0──standard gas concentration, μg / m3;
h0──average peak height, mm.
6.3 Use a microsyringe to inject 10 μL of sample gas into the sample for measurement. Follow the operation in 6.2.2 to determine the retention time. At the same time, the air without halogenated hydrocarbon peak is taken as a blank. Measure the peak height, subtract the blank peak height and the difference from the sample peak height, and find out the content of chloroform and carbon tetrachloride on the standard curve.
7 Result calculation
7.1 Convert the sampling volume to the sampling volume in the standard state according to formula (2):
V = Vt × T / (T + t) × P / P0 .............................. (2)
In the formula: V-sampling volume in the standard state, L;
Vt-sampling volume, which is 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, ℃;
P0──Atmospheric pressure in standard state, 101.3kPa;
P──Atmospheric pressure at the sampling point during sampling, kPa.
7.2 Calculation of the concentration of chloroform and carbon tetrachloride in the air:
7.2.1 The standard curve is calculated according to formula (3):
c = a / V ................................................ .. (3)
In the formula: c──mass concentration of chloroform and carbon tetrachloride in the air, mg / m3;
a──The concentration of chloroform and carbon tetrachloride in the sample, μg;
V-sampling volume under standard conditions, L.
7.2.2 The correction factor can be calculated according to formula (4):
c = (h-h0) ¦ /V......................................(4 )
In the formula: ¦ ──The correction factor measured by 6.2.2, μg / mm.
Other symbols are the same as above.
8 Method characteristics
8.1 Detection limit When the injection volume is 10 μL, the detection limit is 0.15 mg / m3 for chloroform; 0.03 μg / m3 for carbon tetrachloride.
8.2 Precision When the concentration of chloroform is 4mg / m3 ～ 30mg / m3, the coefficient of variation of the eight repeated measurements in the four laboratories is 6.0% ～
2.0%.
When the concentration of carbon tetrachloride is 0.5mg / m3 ～ 2.0mg / m3, the coefficient of variation of 8 repeated measurements in the four laboratories is 5.8% ～ 1.2%.
8.3 Accuracy When the concentration of chloroform is 4mg / m3 ～ 30mg / m3, the average recovery rate is 92.8% ～ 100.1%.
When the concentration of carbon tetrachloride is 0.5mg / m3 ～ 2.0mg / m3, the average recovery is 99.4% ～ 99.8%.
8.4 Measurement range When the injection volume is 10μL, the detection range of chloroform is 0.15mg / m3 ～ 30mg / m3, and the detection range of carbon tetrachloride is 0.03mg / m3 ～ 4mg / m3.
8.5 Interference and elimination Due to the use of gas chromatography separation technology, chloroform, carbon tetrachloride and the coexistence of trichloroethylene, dichloromethane, 1.1-dichloroethane, tetrachloroethylene, etc. are completely separated without interfering with the measurement.
Appendix A
Examples of chromatographic analysis conditions and chromatograms (reference)
A1 Chromatographic analysis conditions Chromatography temperature: 50 ℃;
Detection room temperature: 300 ℃;
Gasification chamber temperature: 300 ℃;
Carrier gas (N2) flow rate: 30mL / min.
A2
0─air; 1─dichloromethane; 2─trichloromethane; 3─dichloroethane;
4─Carbon tetrachloride; 5─Trichloroethylene; 6─Tetrachloroethylene additional instructions:
This standard was proposed by the Health Standards Technical Committee of the Ministry of Health of the People's Republic of China.
This standard is under the jurisdiction of the Chinese Academy of Preventive Medicine.
This standard is drafted by the Liaoning Provincial Sanitation and Epidemic Prevention Station, the Liaoning Provincial Food Sanitation Supervision and Inspection Institute, the Liaoyang Sanitation and Epidemic Prevention Station, and the Shenyang Epidemic Prevention Station.
The main drafters of this standard: Wu Xiaofang, Yang Ming, Lian Wei, Shen Baili, Wang Meihan, Jiang Shuqiu, Wu Bailu, Yuan Xuefen.
This standard is entrusted by the Ministry of Health, the technical focal unit of the Chinese Academy of Preventive Medicine, Environmental Hygiene Monitoring Institute to interpret.
