Gas Chromatography – Gas Chromatography (GC) is a commonly used separation technique in analytical chemistry for organic compounds that can be vaporized without being decomposed or rearranged. The gaseous compounds in the mobile phase which is an inert carrier gas interact with a stationary phase, generally a polymer that coats the wall of a column, to allow the compounds to elute at different times. The column is located in an oven where the temperature of the gas in the column is programmed to control the rate of partitioning of the compounds between mobile and stationary phases. The qualitative identification and quantitative measurement of the compounds are determined as they elute (retention time) onto a selective or non-selective detector specific to the class of organic compounds of interest. Typical detectors that are used in environmental chemistry for the determinative measurement of analytes are Electron Capture Detector (ECD) for organochlorine pesticides and PCBs, and Flame Ionization Detector (FID) for non-halogenated volatile organics.
Gas Chromatography/Mass Spectrometry (GC/MS) – GC/MS utilizes the same separation techniques as described in GC whereby a sample is introduced into the GC system, vaporized and the compounds being retained on the stationary phase. The compounds elute from the column at different times based on their affinity to the stationary phase into the mass spectrometer (MS) where the MS will break down each compound into ionized fragments. These fragments are detected using their mass-to-charge ratio. The most common form of ionization is electron ionization (EI) where the compounds are bombarded with free electrons to fragment them. Commonly used mass spectrometer detectors are quadrupole mass spectrometers and ion trap mass spectrometers.
MATERIALS SCIENCE AND FORENSIC SCIENCES LABORATORY
