2008, Volume 11, Issue 21+22
The Analysis of Volatile Organic Compounds in Gaseous and/or Solid Samples
1 National R&D Institute of Cryogenics and Isotopic Technologies – ICSI Rm. Valcea
2 National R&D Institute for Cryogenics and Isotopic Technologies, Ramnicu Valcea
Many Volatile Organic Compounds (VOCs) present health hazards and/or behave as precursors to ozone formation in ambient air. Therefore, it is important to screen for their presence and determine their concentration. Many industrial and waste treatment plants must monitor the air in and around their facilities to avoid excess emissions and to ensure that legal limits are not exceeded. The concentration of volatile organic compounds has increased with the multiplication of stationary and mobile emission sources.
The volatile organic compounds include a large number of substances, from which some are toxic for humans and harmful to the environment (benzene, 1,3-butadiene, solvents, evaporations from foams, adhesives, floor coverings, elastomers, plastic or molding materials etc.) and some are part of atmospheric cycles – ozone precursors (ethane, ethylene, xylenes, trimethylbenzenes etc.). VOCs are a complex mixture of substances that are present in the ambient air in concentrations of 100 ppt – 10 ppb. Because of that, the determination of VOCs needs sample preconcentration and a good resolution of the analyzer.
One of the techniques used in the determination of volatile and semi-volatile organic compounds in gaseous and solid samples is the thermal desorbtion coupled with a GC/MS (gas-chromatograph/mass spectrometer). This technique requires (in the case of a gaseous sample) collecting the target compounds on solid adsorbents, while the solid samples can be analyzed directly. An advantage of this technique is the possibility of increasing the volume of sample gas that will lead to the detection of a smaller concentration of contaminants.
Usually, one cubic liter of gas is analyzed, that is passed over a solid adsorbent, using an automated sampling pump that controls the transferred volume of gas. The organic compounds are evaporated by rapid heating of the solid adsorbent, followed by the insertion in the cryo trap (-100°C) and the injection in the gas-chromatograph after rapid heating of the cryo trap to 250°C.
Tag search -