is the method of separating and analyzing the components of a chemical mixture; commonly used in the analysis of many types of petroleum products. The test sample is introduced into the chromatograph by means of an injection port, which leads to a column inside an oven. In gas chromatography the sample is volatilized and carried into the column by pressurized inert gas. The sample components are absorbed into a liquid (called the stationary phase) present inside the column. Regulating the oven temperature causes the sample components to reach the detector at the column outlet in order of respective boiling points. Each component is identified on the basis of its retention time in the column. The data are shown on a chromatogram in the form of peaks, whose heights represent the concentration of the respective components. In liquid chromatography (also called high-pressure normal phase liquid chromatography) the sample is carried through the column by an inert liquid and passes through a packing of tiny spheres coated with a stationary phase. The time required for specific components to emerge from the column is directly proportional to their degree of solubility in the stationary phase. Each component is identified on the basis of its retention time in the column.

Also see clay/silica gel analysis, ferrography, infrared analysis, mass spectrometer, particle count, spectrographic analysis.