A chromatograph is a device that separates and identifies chemical compounds by passing a gas through columns containing beads that selectively retain or control the rate of movement of different chemical compounds. This may be done based on molecular size (gel filtration chromatography), net electric charge (ion exchange chromatography), or binding characteristics (affinity chromatography). Chromatographs are used in the natural gas industry to analyze the components in a gas stream. This information can be used to determine the heating value (ensuring gas meets pipeline quality standards), to determine specific gravity and hydrocarbon dew points, and to identify trace contaminants.
Chromatographs are used in laboratories, in the field with portable systems, and may also be permanently installed on pipeline or distribution systems. They are commonly used at pipeline interconnects and other key custody transfer points as well as at critical points in a gas distribution system. Often, they are connected to the SCADA system to notify operators when the amount of key gas components is outside of tolerances. Chromatographs are also used in liquified natural gas (LNG) and natural gas liquids (NGL) facilities to analyze the chemical makeup of these commodities.