Analysis of Volatile Organic Compounds in the Air

Volatile organic compounds (VOCs) are the precursors of photochemical smog, which can be divided into hydrocarbon, halogenated hydrocarbon and VOCs containing oxygen. In addition to participating in the photochemical reaction in the atmosphere to form ozone, volatile organic compounds can be further oxidized, affecting the oxidation of the atmosphere and eventually forming secondary organic aerosols, resulting in the deterioration of visibility, which is an important pollutant in the formation of complex atmospheric pollution. In addition, VOCs are easily absorbed by human skin and mucosa, causing acute damage to human health. Some of the substances are also carcinogenic, teratogenic and mutagenic.

VOCs in the outdoor environment mainly come from industrial waste gas from fuel burning and transportation, automobile exhaust gas and photochemical pollution, etc. Indoor smoke mainly results from combustion products such as coal and natural gas, smoking, heating and cooking, construction and decoration materials, furniture, household appliances, cleaning agents and human body emissions, etc.

Analysis of VOCs in air generally includes sample pretreatment and qualitative and quantitative detection.

Pretreatment Methods

Due to the complex composition in the air, air samples need to be pretreated before the detection of volatile organic compounds in the air. At present, common sample pretreatment methods include solid adsorption/carbon disulfide analysis, SUMMA tank sampling /freeze preconcentration and adsorption tube sampling-thermal desorption, etc. Solid adsorption/carbon disulfide analysis needs solvent parse, causing environmental pollution and a great harm to human body. Therefore, air samples are usually pretreated by SUMMA tank sampling/freeze preconcentration and adsorption tube sampling - thermal desorption, with the advantages of no solvent pollution, simple operation, rapid analysis, high sensitivity, high accuracy and so on.

Qualitative & Quantitative Analysis

Currently, common analytical methods include gas chromatography-mass spectrometry (GC-MS), Proton-Transfer-Reaction Time-of-Flight Mass spectrometry (PTR-TOF-MS), etc.

GC-MS is the most commonly used high-sensitivity method for the detection of volatile and semi-volatile organics, so people always use GC-MS for VOCs detection. It can be used for both quantitative and qualitative analysis and can meet the requirements of trace organics analysis. GC has high separation efficiency and is able to obtain abundant information about chemical structure from trace samples. It can not only separate organics with complex and multi-component traces, but also further enhance the ability of mass spectrometry identification. However, the component loss and cross contamination in the sample during the transfer process may lead to the deviation of test results. Felix Anyakudo, etc. developed an automated headspace GC-MS method for the analysis of full range VOCs, characterized by clean analysis with minimal interference.

PTR-TOF-MS represents an innovative technique for VOCs detection to couple a high-resolution time-of-flight mass spectrometer (TOF-MS) with a PTR ion source. It has the advantages of wide quality range, fast response speed, high resolution and high sensitivity. Moreover, this tool is able to detect molecules with limits of detection (LOD) lower than parts-per-trillion by volume (pptv) range, thereby providing quantitative and qualitative information on the VOCs involved during production, processing and use of any product within its production chain. C. Taiti, etc. used PTR-TOF-MS tool to analysis the characterize of the VOCs which release from 14 different species samples. These studies have shown the great potential and the rapidity of the PTR-TOF-MS to become a commercial standard tool for monitoring VOCs emitted.

References

• Felix Anyakudo, Erwin Adams, Ann Van Schepdael. (2018) ‘Analysis of volatile organic compounds in fuel oil by headspace GC-MS’, International Journal of Environmental Analytical Chemistry, 98(4):323-337.

• Jinling Tian, Jianwei Tan, Naitao Hu, Tingjie Liu, Yulong Wang, Hao Zhong, Jin Cheng, Xuemin Zhang. (2018) ‘Characteristics analysis for total volatile organic compounds emissions of methanol-diesel fuel’, Journal of The Energy Institute, 91(4):527-533.

• C. Taiti, C. Costa, W. Guidi Nissim, S. Bibbiani, E. Azzarello, E. Masi, C. Pandolfi, F. Pallottino, P. Menesatti, S. Mancuso. (2017) ’Assessing VOC emission by different wood cores using the PTR-TOF-MS technology’, Wood Science and Technology, 51:273-295.

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