What is Gas Chromatography?
Gas chromatography (GC) is a powerful analytical technique for the separation and identification of volatile compounds (often organic molecules or gases) present in a gaseous or volatile liquid sample, to determine their presence or absence or quantities. It operates on the fundamental principle of differential mobility, taking advantage of the different affinities of different compounds for stationary and mobile phases. By exploiting these differences, GC is able to separate and quantify complex mixtures with exceptional precision and accuracy.
How Does Gas Chromatography Work?
The working mechanisms of gas chromatography are complex and fascinating. The process begins with the injection of the sample into the GC system. As the sample is carried through the column by the mobile phase (called the carrier gas), the compounds interact differently with the stationary phase. Those compounds with greater affinity migrate more slowly and remain in the column for longer. Conversely, compounds with weaker affinities elute more quickly and remain in the column for a shorter period of time. As a result, compounds take different times to reach the column outlet, so that the mixture is separated into components, and the detector measures the amount of each compound.
Components of a Gas Chromatography System
The configuration of the GC system is very simple. A GC system consists of three main components: a sampling unit, which heats a liquid sample and vaporizes it; a chromatography column, which separates each compound; and a detector, which detects the compound and outputs its concentration as an electrical signal. At the heart of a GC system is the column. This long, thin coil contains a stationary phase, a material with a specific affinity for different compounds.
| Components |
Description |
| Carrier gas supply |
It allows the mobile phase to flow continuously through the column. As the mobile phase transports solutes through the column, it is often referred to as the carrier gas. Ultrapure helium, hydrogen, or nitrogen is used as the carrier gas. |
| Injector |
It is a device that introduces a gaseous or liquid sample into the column head. Liquid samples are usually injected using a microliter syringe, while gases are injected via a gas-tight syringe or gas valve. |
| Column
|
Chromatographic columns are often considered to be the heart of a GC system. A packed or capillary column with a liquid or solid stationary phase is used. |
| Column oven |
The column oven houses the column. The oven is an air thermostat to provide a constant (isothermal) or defined (programmed) increase of the column temperature. The column oven is always equipped with a ventilator to guarantee strong air circulation, because air has poor heat conductivity. |
| Detector |
The detector is a device to record the solutes upon leaving the column. An electric signal is produced, in most cases amplified, and sent to the data system. |
| Data processor |
It is used to register, store, and analyze the data produced. |
Fig. 1 Scheme of a typical GC system (gas chromatograph) (Dettmer-Wilde, K.; Engewald, W.).
Types of Gas Chromatography
Gas chromatography encompasses a variety of variants, some prominent types of GC include:
- Gas-Liquid Chromatography (GLC): In GLC, the stationary phase is a liquid immobilized on an inert solid support. This technique is particularly effective for separating volatile organic compounds.
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Gas-Solid Chromatography (GSC): GSC employs a solid stationary phase, such as a porous solid or a packed bed of particles. It is commonly used for the analysis of inorganic gases and light hydrocarbons.
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Capillary Gas Chromatography (CGC): CGC employs a capillary column, which is significantly narrower in diameter compared to conventional GC columns. This variant offers enhanced separation efficiency and sensitivity.
Gas chromatography is used in a range of industries for its ability to separate, analyze and quantify volatile compounds with exceptional precision and sensitivity. Some notable applications of GC include environmental monitoring, forensic science, petrochemical analysis, pharmaceutical analysis, cosmetics and fragrance industry, and food safety. In short, gas chromatography provides powerful analytical tools for scientific research, industrial production and environmental protection, and promotes the development and progress of various industries.
Reference
- Dettmer-Wilde, K.; Engewald, W. Practical gas chromatography. A Comprehensive Reference. Springer, 2014: 902.
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