Gas and volatiles analysis in ECCD
Permanent gases are defined as compounds that have a gaseous form at atmospheric pressure and room temperature. In contrast, volatile organic compounds (VOCs) are organic chemical compounds in liquid or in some cases solid state that evaporate (sublimate) easily at room temperature. This behavior is caused by high vapor pressure resulting from low boiling (or sublimation) point. Diverse definitions of the term VOC are in use. The European Union reflects the best the chemical properties of these compounds by defining VOC as "any organic compound having an initial boiling point less than or equal to 250 °C measured at a standard atmospheric pressure of 101.3 kPa”.
Both permanent gases and VOCs are part of the environment and are also often products or side products of chemical reactions. VOCs are formed in a wide range of activities and manufacturing processes such as printing, surface cleaning, vehicle coating, dry cleaning, and manufacture of footwear and pharmaceutical products. Other important sources of VOCs are indoor coatings like decorative paints and varnishes or materials used in car interiors. Permanent gasses can be present as free gas in the environment, can be dissolved in liquids, or adsorbed in the pores of solid material. They form a great majority of the air pollutants. Both gases and volatiles can have an unpleasant smell and can be harmful to human health, even when there is no smell detected.
All the factors mentioned above make the analysis and detection of gasses and volatiles important but challenging. ECCD has a broad range of sampling and detection techniques available and holds the expertise for the analysis of gases/volatiles and their mixtures in bulk concentration or in trace amounts.
The great majority of analytical techniques consist of sample introduction, the analysis itself and the detection part. An appropriate sample introduction technique is the core of each analytical method but is especially important in gas analysis. A gaseous compound of interest can be present in different forms and places requiring suitable sampling techniques. E.g. gas samples from the environment and production facilities are usually taken with the help of a pump and stored in metal cylinders or gas sampling bags. Bulk gas concentrations are then the best analyzed using porous layer open tubular (PLOT) gas chromatography columns and detected by a thermal conductivity detector. The technique of choice to analyze traces of volatiles in an inert matrix such as air or nitrogen is selected ion flow tube mass spectrometry (SIFT-MS) but this technique will not work when the matrix is ionizable. In that case PLOT column in combination with the helium ionization detector (HID) is more likely to provide the answer for permanent gases and headspace gas chromatography with appropriate detection for VOCs. The most used detectors are flame ionization (FID), thermal conductivity (TCD), mass spectrometry (MS), or electron capture (ECD) detector. The gaseous/volatile analyte can also be trapped and pre-concentrated on a sorbent and analyzed on a thermal desorption unit connected to a gas chromatograph.
Inner and outer air pollution is a growing problem where the development of materials able to efficiently remove these pollutants can contribute to a solution. A suitable test chamber and fast analytical technique are the key elements in the characterization of such materials. In ECCD we have extensive experience in designing set-ups and providing data crucial in the evaluation of the material performance. There are glass flow chambers available with volumes from 1 to 4 L which can be connected to fast GC or SIFT-MS depending on the purpose of the test. Fully automated microchambers with 100 mL volume enable parallel testing of up to four materials and can be used in combination with GC or SIFT-MS. Permeability testing of e.g. materials used for personal protection equipment or packaging can be performed too with the use of a permeation accessory.
Another possibility to analyze the composition of permanent gases is Fourier transform infrared spectroscopy (FTIR) with the use of a special gas cell. This technique can analyze simultaneously a wide variety of gases except diatomic or noble gases such as O2, N2, H2, He, or Ar.
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