Gaseous Pollutants - Gas Chromatography (GC)

Figure: Schematic gas chromatography

Gas chromatography (GC)
Gas chromatography (GC) coupled with a flame ionization detector (FID) is employed for qualitative identification and quantitative determination of volatile organic compounds (VOCs) in air pollution monitoring. The gas chromatograph, or GC, consists of a column, oven and detector. In the gas chromatograph, a sample goes to the column, separates into individual compounds and proceeds through the hydrogen flame ionization detector. The flame in a flame ionization detector is produced by the combustion of hydrogen and air. When a sample is introduced, hydrocarbons are combusted and ionized, releasing electrons. A collector with a polarizing voltage located near the flame attracts the free electrons, producing a current that is proportional to the amount of hydrocarbons in the sample. The signal from the flame ionization detector is then amplified and output to a display or external device.

Gas Chromatography-mass Spectrometry
Gas chromatography-mass spectrometry (GC-MS) instruments have also been used for identification of volatile organic compounds. Mass spectrometers use the difference in mass-to-charge ratio (m/z) of ionized atoms or molecules to separate them from each other. Mass spectrometry is useful for quantification of atoms or molecules and also for determining chemical and structural information about molecules. Molecules have distinctive fragmentation patterns that provide information to identify structural components.