VOC: Volatile Organic Compounds Over Years
Volatile organic compounds, or VOCs (VOC-English) are compounds of carbon and dhydrogane can easily become gaseous in the atmosphere. They may be of anthropogenic origin (refining, evaporation of organic solvents, unburned ...) or natural (emissions by plants).
Indeed, VOCs participate in photochemical reactions in the lower atmosphere, causing the upturn in dozon concentration in the troposphere, an indirect effect on health. The modified cycle Chapman due to radicals generated by the presence exacerbates dozon VOCs into the atmosphere.
Between 1970 and 1990 the tropospheric ozone concentration for EUROPE from 10 ppm to 50 ppm (ppm: parts per million), an increase of more than 2.4% per year in the last 20 years. This is strongly related to lasthme both among young people than among the elderly. Some VOCs are also harmful to plant and animal species. Ozone sources also has an effect on deciduous trees, plants, vegetables and fruits. The climate is also modified by the presence of greenhouse gas emissions. An increase in global temperature of Earth is driven by the increasing presence dozon, which absorbs in linfrarouge 2000 times more than carbon dioxide in the terrestrial radiation. VOCs are adsorbed on different solids (clays and silts) or transferred in water by aeration, thus affecting the quality of drinking water.
VOCs have a direct impact on health. Several standards of quality lair were established in the past to protect humans against the various air pollutants that can harm health. In this battle, lexposition to vapors of benzene was directly associated with leukemia. Then, the carcinogenic effects of 1,3-butadiene have been made.
It is difficult to determine the VOC limits in the air facing the ambient, due to the complexity of the chemistry between these molecules and diseases contracted. Some VOCs have direct effects on the human body such as tetrahydrofuran sattaquant liver and nerves affecting the heart Trichloroethylene and carcinogenic, and glycol ethers of short chain, with a specific toxicity to the spinal bone and testicles, are teratogenic. Limpact particles of dust, photochemical smog and acid aerosols, dazote oxides and sulfur, and carbon monoxide, metals and VOCs has been studied by Bates (1995). However, little information on the effects of long-term is available up to now due to lack of perspective studies.
VOCs and associated molecules are carcinogenic. A recent study confirmed this risk [5] from an epidemiological study that focused on Rhone-Alpes on 37 pollutants (unregulated lair for the quality of ambient and rarely measured). The study has shown that these pollutants tend to diminish as the exposure to formaldehyde may lead to irritation of the eyes, nose and throat, and that some VOCs lexposition (Vinyl chloride monomer, benzene, 1, 3-butadiene, Tetrachloroethylene, acetaldehyde, formaldehyde and 1,2-dichloroethane) increases, a small but statistically detectable way.
Perchloroethylene, used for dry cleaning, is on the list of group 2A carcinogens by IARC.
Three techniques for recovering compounds can be performed: solvent extraction (soxhlet), supercritical fluid (sample and is bringing its supercritical state, between the liquid and gaseous phase) or by thermal desorption cartridges or ladsorbant used.
The VOC sample in storage can be performed for a few days under normal conditions. However, it can not exceed more than three weeks. Sample and is should be kept away from light and refrigeration.
The standardization is done by creating an atmosphere of static or dynamic (constant flow) and by introducing stable compounds and gases in a known volume, so that the concentration of each compound present can be calculated for quantification after analysis. Lazote gas is often used as a solvent in the preparation of standard solutions.
The separation of compounds of guidelines may be ugly at different chromatographic methods available on the market today. The high-performance liquid chromatography (HPLC) is used when gaseous sample and is solvated in a liquid. Universal detectors can be used as promoting the absorption UV-vis, spectroscopy Fourier transform infrared (FTIR) or differential refractometer, which provides a limit of detection (LOD) of 1ng. Secondly, fluorimetry, lelectrochimie, radioactivity and conductivity measurements are used to detect certain compounds more specific, depending on the properties of each face different detectors available.
The gas chromatography (GC) is used to separate the compounds present in the sample and they may be detected by thermal conductivity (TCD), comparison between the conductivity of the carrier gas and that gas, with detection limits of 1 to 10ng. A second mode of detection is universal lionisation flame (FID) with an LD 2 4PG. The detectors capture delectrons (DCE), or for thermionic lazote and phosphorus (NPD) can be coupled to the GC for detection of more specific compounds.
The linking of Mass Spectrometry (MS) to HPLC or GC allows structural identification of compounds, especially if used in MS / MS. Nuclear magnetic resonance (NMR) is limited and not well studied in research, but could be a structural technique didentification.
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