Gas Chromatography is a technique which divides a gas Mixture to ascertain the presence and concentration of gases and impurities in a sample. Applied properly, GC can measure down to ppb levels, which makes it ideal for use in high purity processes. In GC, gas mixture components are separated by means of a gas Sample, with an inert carrier gas, into a flow-through round tube called a column. The different gas components are separated because of their interaction with the column material, which trigger different molecules in the sample to elute at different times. These particular retention times are detected by a sensor in the column exit, as the individual molecular properties of each gas make it travel through and exit at another time. The comparison of retention times enables users to qualitatively Identify gas types from the sequence in which they elute from the column.

If conditions are continuous, a specific gas chromatography will elute with the exact same retention period, allowing specific gas types to be deduced from the region of the peak. Additionally, the relative quantity of each gas concentration may also be measured by the sensor as every gas elutes from the column. The conditions by which GC works for a given program are Invariably different and require individual optimisation. Nearly all GC analysers are therefore present in the factory, with program specific valve timings, temperature and flow settings and peak detection parameters. A gas chromatograph uses two kinds of columns. Packed columns measure one and a half to ten meters in length. They also have an inner diameter measuring two to four millimetres.

The narrow tube is normally made from glass and a number of others are made from stainless steel material. The columns are packed with divider, solid and inert support material. The internals are coated with liquid stationary phase or strong. The coating materials determine the sort of samples or materials will be consumed strongly. Several columns are constructed up to separate various kinds of sample compounds. Capillary columns kind is the other kind of columns which are made of smaller diameter and with lengths step at about twenty five to sixty meters. The inner walls are coated with active substances and use polyimide to coat the externals. All of these are flexible that enable a column to be converted into a coil.