A Gas Chromatograph is a chemical analysis instrument for separating chemicals in a complex sample.
A gas chromatograph uses a flow-through narrow tube known as the column, through which different chemical constituents of a sample pass in a gas stream (carrier gas, mobile phase) at different rates depending on their various chemical and physical properties and their interaction with a specific column filling, called the stationary phase.
As the chemicals exit the end of the column, they are detected and identified electronically.
The function of the stationary phase in the column is to separate different components, causing each one to exit the column at a different time (retention time).
Other parameters that can be used to alter the order or time of retention are the carrier gas flow rate, column length and the temperature.