The Gas Chromatography/Mass Spectrometry (GC/MS) instrument separates chemical mixtures (the GC component) and identifies the components at a molecular level (the MS component). It is one of the most accurate tools for analyzing environmental samples. The GC works on the principle that a mixture will separate into individual substances when heated. The heated gases are carried through a column with an inert gas (such as helium). As the separated substances emerge from the column opening, they flow into the MS. Mass spectrometry identifies compounds by the mass of the analyte molecule. A ÒlibraryÓ of known mass spectra, covering several thousand compounds, is stored on a computer. Mass spectrometry is considered the only definitive analytical detector.

GC/MS is a technique that can be used to separate volatile organic compounds (VOCs) and pesticides. Portable GC units can be used to detect pollutants in the air, and they are currently used for vapor intrusion investigations. However other uses of GC or MS, combined with other separation and analytical techniques, have been developed for radionuclides, explosive compounds such as Royal Demolition Explosive (RDX) and Trinitrotoluene (TNT), and metals. Some of these are described below. A type of spectrometry can also be used to continuously monitor incinerator emissions, in place of a standard method that collects samples from a gas stream for laboratory analysis. That standard method has a relatively long turn around time, and it does not provide information that catastrophic releases have occurred or that there is a system failure. With real-time, continuous monitoring, all releases are monitored, and if there is a system breakdown, the system can be turned off and/or the nearby community can be notified.