Determination of volatile organic compounds

- Jul 07, 2020-

In order to implement the "Environmental Protection Law of the People's Republic of China", protect the ecological environment, protect human health, improve the management level of the ecological environment, and regulate the monitoring of the ecological environment, the Ministry of Ecology and Environment decided to develop the "Determination of Volatile Organic Compounds in Ambient Air" by portable gas chromatography-mass spectrometry National Environmental Protection Standards. At present, the standard preparation unit has completed the draft for consultation. In accordance with the requirements of the Administrative Provisions on the Preparation and Revision of National Environmental Protection Standards(Guohuangui Technology [2017] No. 1), we are now seeking comments on the standards (draft for soliciting comments). Please study carefully and submit written comments on June 30, 2020 A few days ago, the opinions were sent back to the Ministry of Ecology and Environment by letter or e-mail. Those who did not respond within the time limit will be treated as no comments.

Excerpts from the content of the standard:

 

This standard specifies portable gas chromatography-mass spectrometry for the determination of volatile organic compounds in ambient air.

 

This standard is applicable to the determination of 52 kinds of volatile organic compounds such as toluene in ambient air and unorganized emission monitoring points of pollution sources. Other volatile organic compounds can also be determined by this standard if they pass the method suitability verification.

 

Normative references: "HJ/T 55 Technical Guidelines for the Monitoring of Unorganized Emissions of Air Pollutants", "HJ 194 Technical Specifications for Manual Monitoring of Ambient Air Quality", and "HJ 604 Determination of Total Hydrocarbons, Methane and Non-Methane Hydrocarbons in Ambient Air" Direct Injection-Gas Chromatography", "HJ 759 Determination of Volatile Organic Compounds in Ambient Air Canister Sampling/Gas Chromatography-Mass Spectrometry", "HJ 759 Determination of Volatile Organic Compounds in Ambient Air Canister Sampling/Gas Chromatography-Mass Spectrometry", " HJ 589 Technical Specifications for Emergency Monitoring of Environmental Emergencies.

 

Method principle

 

After adsorption and thermal desorption, the ambient air sample is separated into gas chromatography and detected by a mass spectrometer.

 

For 52 target compounds, qualitative by comparison with the standard substance mass spectrum and retention time, quantification by internal standard method; for 52 target compounds, preliminary qualitative by comparison with the standard substance mass spectrum, according to their response value and internal standard response The ratio of values to estimate its concentration.

 

Instruments and equipment

 

Portable gas chromatography-mass spectrometer: sampling module with temperature control function, adsorption thermal desorption module, gas chromatography module (with program heating function), and quadrupole or ion trap mass spectrometry module, with automatic addition of internal standard function. The mass spectrometer module has a 70 eV electron bombardment (EI) ion source, with full scan/selective ion scan, automatic/manual tuning, library search, and quantitative analysis.

 

Capillary column: 15 m×0.25 mm, 1.0 µm film thickness (100% dimethyl polysiloxane solid phase) or other equivalent capillary column as required.

 

Gas dilution instrument: The maximum dilution factor is not less than 100 times.

 

Sampling tank: stainless steel tank with inert treatment on the inner wall, pressure resistance value> 241 kPa, which should meet the relevant requirements of HJ 759.

 

Airbags: Fluoropolymer film airbags should meet the relevant requirements of HJ 732.

 

Vacuum pressure gauge: The maximum allowable error should not exceed 1 kPa (0.14 psi), and the pressure range: -101 kPa~202 kPa. 7.7 Connector: used to connect the sampling tank (7.4) to the air bag (7.5).

Reference conditions for adsorption thermal desorption module

 

Heating equilibrium temperature 50 °C; heating equilibrium time 10 min; sampling needle temperature 60 °C; transfer line temperature 60 °C; measuring ring volume is 200 μl or 400 μl.

 

Adsorption tube sampling flow rate: 100 ml/min; injection volume: 5 ml to 600 ml; adsorption tube desorption temperature: 300 °C; adsorption tube pre-desorption time: 0.1 min; adsorption tube desorption time: 0.5 min.

 

Reference conditions for gas chromatography

 

Column flow rate (constant flow mode): 1.0 ml/min or 0.2 ml/min; programmed temperature: 60 °C for 3 min, 18 °C/min to 130 °C, and then 30 °C/min to 200 °C, hold at 200 C for 1 min.

 

Reference conditions for mass spectrometry Ion source: EI; ionization energy: 70 eV; scan method: full scan; scan range: 41 amu ~300 amu; other parameters can be set with reference to the instrument instruction manual, or select ion scan mode.