Chromatography facilitates separation of distinct molecules within a mixture based on their respective chemical properties, and how those properties interact with the substrate coating the chromatographic column. This separation can happen “on-line,” during the measurement itself, or prior to measurements to isolate a pure compound. Gas and liquid chromatography have distinct advantages, based on the molecules of interest. For example, aqueously soluble molecules are more easily separated with liquid chromatography, while volatile, nonpolar molecules like propane or ethane are separated with gas chromatography.