original_query: What is gas chromatography-mass spectrometry (GC-MS) and how does it work?
query: What is gas chromatography-mass spectrometry (GC-MS) and how does it work?
answer: Gas chromatography-mass spectrometry (GC-MS) is an analytical method combining gas chromatography and mass spectrometry to identify substances in a sample.  Gas chromatography separates the molecules in a mixture based on their different affinities for a stationary phase in a column. The separated molecules then enter a mass spectrometer, which ionizes them, fragments them, and detects the fragments based on their mass-to-charge ratio. Combining the separation and detection allows for highly accurate identification of substances.