Gas-Liquid Chromatography (GLC) is a separation technique in which gas (usually inert gas, such as helium or nonreactive gas, such as nitrogen), is used as a mobile phase (Figure 1) , and liquid as a stationary phase. Basis of separation is difference in partition coefficient of volatilized compounds between liquid and gas phases when the desired compound is carried through the column by a carrier gas.
Typical application of GLC includes testing purity of a substance, prepare new compounds from mixture (preparative chromatography), identifying and separating different components of a mixture. It is also known as Vapor-Phase Chromatography (VPC), or Gas-Liquid Partition Chromatography (GLPC).
GLC is based upon partitioning of compounds between stationary liquid and mobile gas phase. Due to its high sensitivity, reproducibility, and speed of resolution, it is widely used for several qualitative and quantitative analyses.
The gaseous compounds being analyzed interact with the walls of column, which is coated with different kinds of stationary phases. This causes each compound to elute at different time (retention time), and then retention times are compared. This makes GLC analytically very useful. As compound leaves the column, they pass through a detector, which is linked to chart recorder via amplifier. Chart recorder records the peaks (Figure 3).
A flow diagram representing the steps involved in the process of gas-liquid chromatography is shown below (Figure 4).
Applications of Gas-Liquid Chromatography
Gas liquid chromatography has a very wide field of application in the separation and analysis of multi component mixtures such as essential oils, hydrocarbons and solvents. It is one of the primary analytical techniques, which was used in forensic laboratory.
- GLC is combined with mass spectroscopy (GC/MS) for drug detection, fire investigation, environmental analysis, explosives investigation, and identification of unknown samples.
- GC/MS is also used in airport security to detect unwanted substances. Non derivatized sugars and sugar alcohols are successfully analyzed by GC/MS using atmospheric pressure chemical ionization (APCI) in negative ion mode.
- GC is widely used by forensic scientists for an analysis of body fluids for the presence of illegal substances, testing of fiber and blood from a crime scene, and to detect residue from explosives.