Standard Test Method for Sanitary Test 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.
This standard applies to the determination of the concentration of chloroform and carbon tetrachloride in the atmosphere of residential areas. It is also applicable to the determination of chloroform and carbon tetrachloride in the air of public places.
2 Principle
After chloroform and carbon tetrachloride are completely separated from the coexisting program control substance in the column, they are measured by an electron capture detector, characterized by retention time, and quantified by peak height.
3 reagents and materials
3.1 Trichloromethane: chromatographically pure.
Carbon tetrachloride: chromatographically pure.
1.1-Dichloroethane, trichloroethylene, tetrachloroethylene, dichloromethane: all 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 an electron capture detector.
4.2 Column: Glass column with a length of 2m and an inner diameter of 3mm, with SE-30 stationary phase.
4.3 Gas bag: plastic aluminum foil composite film gas bag, volume 400mL.
4.4 Syringes: 100 mL, 50 mL, 1 mL, 1 μL, 10 μL, 100 μL.
4.5 Oven: 0 ~ 200 ° C.
The above equipment is pre-cleaned, and the gas chromatograph should be injected without halogenated hydrocarbon peaks.
5 sampling
Use a syringe to drive the air into the gas bag, make it full, and then let it go. Repeat this three times, after the Zui is full, seal the inlet with a silicone rubber pad. Write a label, indicating the time and place.
6 Analysis steps
6.1 Chromatographic conditions often vary depending on the experimental conditions. Therefore, the chromatographic conditions for the analysis of chloroform and carbon tetrachloride should be based on the type and performance of the gas chromatograph used (see Appendix A).
6.2 Drawing of standard curves and determination of correction factors
6.2.1 Preparation of standard gases
a 0.34 μL (d 20 ° C / 4 ° C 1.47) chloroform was injected into a 100 mL syringe filled with a small aluminum foil filled with nitrogen, placed in an oven (70 ~ 80 ° C), mixed and balanced for 10 min, placed at room temperature stable After that, the standard gas concentration was 5 μg/mL.
b. 0.31 μL (d 20 ° C / 4 ° C 1.62) carbon tetrachloride was injected into a 100 mL syringe in the same manner with a standard gas concentration of 5 μg/mL.
6.2.2 Drawing of the standard curve
Take 4 nitrogen-filled 100mL syringes, add chloroform standard gas 0, 40, 80, 120μL (concentration is 0, 2, 4, 6μg / L) and carbon tetrachloride standard gas 0, 10, 30, 50 μL (concentration of 0, 0.5, 1.5, 2.5 μg/L). The above-mentioned respective concentrations of standard gas were repeatedly measured, and 10 μL was taken into a gas chromatograph to record the retention time, and a standard curve was prepared by using the average peak height or peak area and the concentration of chloroform and carbon tetrachloride.
6.2.3 Determination of correction factors
At the same time of sample analysis, take the chloroform and carbon tetrachloride standard gases close to the sample, and determine the retention time and average peak according to the operation of 6.2.2. Calculate the correction factor according to formula (1):
¦ =c0/h0 ....................................(1)
Where: ¦ ─ correction factor;
C0──standard gas concentration, μg/m3;
H0 - average peak height, mm.
6.3 Sample determination
Use a micro-injector to enter the sample gas 10 μL and operate according to item 6.2.2 to characterize the retention time. At the same time, the air without the halogenated hydrocarbon peak is taken as a blank. The peak height was measured, and the peak height and the difference were subtracted from the peak height of the sample, and the contents of chloroform and carbon tetrachloride were detected on the standard curve.
7 Calculation of results
7.1 Convert the sampling volume to the sampling volume in the standard state according to equation (2):
V=Vt×T/(T+t)×P/P0..............................(2)
Where: V——the sampling volume in the standard state, L;
Vt——sample volume, which is obtained by multiplying the sample flow by the sampling time, L;
T──Absolute temperature under standard conditions, 273K;
T——the temperature of the sampling point at the time of sampling, °C;
P0——Atmospheric pressure under standard conditions, 101.3 kPa;
P——Atmospheric pressure at the sampling point during sampling, kPa.
7.2 Calculation of the concentration of chloroform and carbon tetrachloride in air:
7.2.1 The standard curve is calculated according to formula (3):
c=a/V............................................. ..(3)
Where: c—the 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 equation (4):
c=(h-h0)¦ /V.....................................(4 )
Where: ¦ ─ the correction factor measured by item 6.2.2, μg/mm.
Other symbols are the same as above.
8 Method characteristics
8.1 Detection limit
When the injection volume was 10 μL, the detection limit of chloroform was 0.15 mg/m3; the carbon tetrachloride was 0.03 μg/m3.
8.2 Precision
When the concentration of chloroform is 4 mg/m3 to 30 mg/m3, the coefficient of variation of the repeated determination of the four laboratories is 6.0%.
2.0%.
When the concentration of carbon tetrachloride was from 0.5 mg/m3 to 2.0 mg/m3, the coefficient of variation of the eight replicates in four laboratories was 5.8% to 1.2%.
8.3 Accuracy
When the concentration of chloroform is from 4 mg/m3 to 30 mg/m3, the average recovery is from 92.8% to 100.1%.
When the concentration of carbon tetrachloride is from 0.5 mg/m3 to 2.0 mg/m3, the average recovery is from 99.4% to 99.8%.
8.4 Measurement range
When the injection amount is 10 μL, the detection range of chloroform is 0.15 mg/m3 to 30 mg/m3, and the detection range of carbon tetrachloride is 0.03 mg/m3 to 4 mg/m3.
8.5 Interference and elimination
Due to the use of gas chromatography separation technology, chloroform and carbon tetrachloride are completely separated from the coexisting materials such as trichloroethylene, methylene chloride, 1.1-dichloroethane, tetrachloroethylene, etc., and do not interfere with the measurement.
Appendix A
Chromatographic conditions and chromatograms
(reference piece)
A1 chromatographic conditions
Chromatography temperature: 50 ° C;
Detection chamber temperature: 300 ° C;
Gasification chamber temperature: 300 ° C;
Carrier gas (N2) flow rate: 30 mL/min.
A2
0-air; 1-dichloromethane; 2-trichloromethane; 3-dichloroethane;
4-carbon tetrachloride; 5-trichloroethylene; 6-tetrachloroethylene
Additional information:
This standard was proposed by the Health 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 was drafted by Liaoning Provincial Health and Epidemic Prevention Station, Liaoning Food Hygiene Supervision and Inspection Institute, Liaoyang City Health and Epidemic Prevention Station, and Shenyang Municipal Epidemic Prevention Station.
The main drafters of this standard: Wu Xiaofang, Yang Ming, Lian Wei, Shen Baili, Wang Meizhen, Jiang Shuqiu, Wu Bailu, Yuan Xuefen.
This standard is interpreted by the Environmental Health Monitoring Institute of the Chinese Academy of Preventive Medicine, which is entrusted by the Ministry of Health.
|