Determination of 8 sulfur-containing organic compounds, including methyl mercaptan, in exhaust gas from fixed pollution sources using gas bag sampling pre concentration/gas chromatography-mass spectrometry method

Warning: The standard substances used in the experiment are volatile toxic chemicals and should be used under ventilated conditions. When operating, protective equipment should be worn according to regulations to avoid inhalation.

1 Scope of application

This standard specifies the gas bag sampling pre concentration/gas chromatography-mass spectrometry method for determining eight sulfur-containing organic compounds, including methyl mercaptan, in exhaust gas from fixed pollution sources. This standard is applicable to the determination of eight sulfur-containing organic compounds, including methyl mercaptan, ethyl mercaptan, methyl sulfide, methyl ethyl sulfide, carbon disulfide, ethyl sulfide, dimethyl disulfide, and thiophene, in exhaust gases from fixed pollution sources. When the sampling volume is 50.0 ml, the detection limit of sulfur-containing organic compounds determined by this standard is 0.005 mg/m3~0.011 mg/m3, and the lower limit of determination is 0.020 mg/m3~0.044 mg/m3, as detailed in Appendix A.

2 Normative References

This standard references the following documents or their clauses. The valid version of any referenced document without a date is applicable to this standard. GB/T 16157 Sampling methods for particulate matter and gaseous pollutants in exhaust gas from fixed sources HJ 732 Sampling method for volatile organic compounds in exhaust gas from fixed sources HJ 759 Determination of volatile organic compounds in ambient air Can sampling/gas chromatography-mass spectrometry HJ/T 397 Technical specifications for monitoring fixed source exhaust gas

3 Methods and Principles

Collect fixed pollution source exhaust gas with an air bag, concentrate it in a cold trap, perform thermal analysis, and then enter gas chromatography separation for detection using a mass spectrometer detector. Qualitative analysis by comparing with standard substance mass spectrometry and retention time, and quantitative analysis by internal standard method.

4 Interference and Elimination

When high concentrations of other types of volatile organic compounds affect the quantification of sulfur-containing organic compounds, analysis can be carried out by reducing the sample size, diluting the sample, or using a highly selective detector for sulfur-containing compounds.

5 Reagents and Materials

5.1 Standard gas: The concentration of methyl mercaptan, ethyl mercaptan, methyl sulfide, methyl ethyl sulfide, carbon disulfide, ethyl sulfide, dimethyl disulfide, and thiophene 2 ranges from 1.5 μ mol/mol to 2.5 μ mol/mol. High pressure steel cylinders should be stored with a pressure not less than 1.0 MPa, and the storage period should refer to the relevant instructions on the standard gas certificate.

5.2 Standard gas: Use a gas diluter (6.7) to dilute the standard gas (5.1) with nitrogen (5.8) to 15 nmol/mol~25 nmol/mol, and store it in a 6 L tank (6.6) for immediate use.

5.3 Internal standard gas: concentration of 1 μ mol/mol. The internal standard is 1,4-difluorobenzene, stored in high-pressure steel cylinders with a pressure not less than 1.0 MPa. The storage period is specified in the relevant instructions of the standard gas certificate. On the premise of meeting the method requirements and not interfering with the target compound, other substances can also be used as internal standards.

5.4 Internal standard gas: Use a gas diluter (6.7) to dilute the internal standard gas (5.3) with nitrogen (5.8) to a concentration of 100 nmol/mol, and store it in a 6 L tank (6.6) for 20 days.

5.5 4-bromofluorobenzene standard gas: with a concentration of 1 μ mol/mol, stored in high-pressure steel cylinders with a pressure not less than 1.0 MPa. Please refer to the relevant instructions on the standard gas certificate.

5.6 Standard gas for 4-bromofluorobenzene: Use a gas diluter (6.7) to dilute the standard gas for 4-bromofluorobenzene (5.5) with nitrogen (5.8) to a concentration of 100 nmol/mol, and store it in a 6 L tank (6.6) for 20 days.

5.7 Helium: ≥ 99.999%.

5.8 Nitrogen: ≥ 99.999%.

5.9 Liquid nitrogen.

6 Instruments and equipment

6.1 Sampling device: The requirements for the airbag sampling device shall comply with the relevant provisions of HJ 732.

6.2 Gas chromatography-mass spectrometer: The gas phase part has an electronic flow controller, the column temperature box has a programmed heating function, and can be equipped with a column temperature box cooling device. The mass spectrometry section has a 70 eV electron impact (EI) ion source, with functions such as full scan/selective ion scan, automatic/manual tuning, and spectral library retrieval.

6.3 Capillary chromatography column: 60 m × 0.32 mm × 1.04 µ m (dimethyl polysiloxane fixative), or other equivalent capillary chromatography column.

6.4 Gas Cold Trap Concentrator: It has the function of automatic quantitative sampling and automatic addition of standard gas and internal standard, and the reproducibility of sampling is within ± 5%. It should have a three-stage cold trap that can introduce liquid nitrogen for low cooling to -180 ℃, with a heating rate of over 300 ℃/min, to complete three-stage capture and remove interference such as H2O and CO2. The internal pipelines of the concentrator and the connecting pipelines with the gas chromatography-mass spectrometer are made of inert materials and can be heated within the range of 50 ℃~150 ℃.

6.5 Concentrator automatic sampler: It can perform automatic injection of gas bags and tanks, and the internal pipelines are made of inert materials and have pipeline heating function.

6.6 Tank: Stainless steel tank with inert inner wall treatment, with a capacity of 6 L for storing standard gas, a capacity of 0.45 L or other small volume tanks. The pressure resistance value of the tank is greater than 241 kPa.

6.7 Gas Dilution Device: Equipped with pressure dilution function for the tank, the dilution ratio can reach 1000 times.

6.8 Tank cleaning device: capable of evacuating the tank to a vacuum (<10 Pa), with heating, humidification, and pressure cleaning functions.

6.9 Airbag: A fluoropolymer airbag with a minimum volume of 1L.

6.10 Vacuum pressure gauge: Accuracy requirement ≤ 7 kPa, pressure range: -101 kPa~202 kPa.

6.11 Airtight injection needle: 10 ml, with detachable side hole needle and circular hole needle.

6.12 Anode and cathode rapid gas path connector: used to connect the tank (6.6) in series with the gas bag (6.9).