Gas Chromatographs separate volatile compounds by carrying a vaporized sample through a coated column with an inert gas, where each compound elutes at a characteristic time before reaching the detector. Column ovens run from 4 to 450 degrees C, with cryogenic cooling to minus 80 degrees C on selected models, and programmed ramps of 0.1 to 80 degrees C per minute across up to 20 steps. Flame ionization detection reaches 3 x 10^-12 g/s for hydrocarbons, and GC-MS and ion chromatography systems cover identification and ionic analysis. Typical uses include residual solvents in pharmaceuticals, VOCs and pesticides in water, forensic toxicology and petrochemicals.