Gas chromatography–mass spectrometry (GC-MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. It is actually two techniques that are combined to form a single method for analyzing mixtures of organic chemicals. Gas chromatography separates the components of a mixture, and mass spectrometry characterizes each of the components individually. The combination of the two techniques allows for both qualitative and quantitative evaluations of a sample containing a number of organic compounds. The uses for GC-MS are numerous, including chemical, geological, environmental, and forensic research.