Definition of Gas Chromatography
Gas Chromatography (GC) is an analytical technique used to separate, identify, and quantify compounds in a mixture based on their volatility and interaction with a stationary phase.
Basic Components
Injection Port: Where the sample is introduced, usually vaporized into a gaseous state.
Carrier Gas: An inert gas (like helium, hydrogen, or nitrogen) that pushes the sample through the column.
Column: A long, coiled tube where separation occurs. The inside of the column is coated with a stationary phase, which can be a liquid film or a solid support.
Detector: Detects compounds as they elute (come out) from the column. Common detectors include the Flame Ionization Detector (FID) and the Thermal Conductivity Detector (TCD).
Principle
The sample is vaporized and introduced into the GC. As the sample travels through the column, individual compounds interact differently with the stationary phase, leading to varying travel times.
More volatile compounds or those with lesser interaction with the stationary phase will elute faster, while less volatile compounds or those with more interaction will elute slower.
Applications
Widely used in pharmaceuticals, petrochemicals, environmental testing, and food and beverage industries.
Analyzes volatile and semi-volatile compounds with high precision and sensitivity.
Components
Injection Port: Introduces the sample, usually vaporized at a high temperature.
Mobile Phase: An inert gas (e.g., helium, nitrogen, or hydrogen) that carries the vaporized sample compounds through the column.
Column: A coiled tube where separation occurs, either packed with a solid stationary phase or coated with a liquid stationary phase.
Detector: Records the amount of compound exiting the column, providing data to quantify and identify components.
Separation Mechanism
Partitioning: Compounds in the sample partition between the mobile phase (carrier gas) and the stationary phase within the column.
Differential Interactions: Each compound interacts differently with the stationary phase, causing variations in travel speeds.
More Volatile/Less Interaction: Elute faster.
Less Volatile/More Interaction: Elute slower.
Retention Time (RT)
The time taken for a compound to travel from the injection port to the detector.
It's characteristic of a compound under specific GC conditions.
The area under each peak in a chromatogram correlate to the concentration of the compound.
Factors Affecting Separation
Column Temperature:
High temperatures increase elution rates but reduce resolution.
Temperature programming optimizes separation and reduces analysis time.
Carrier Gas Flow Rate:
Affects separation and elution times.
Stationary Phase:
Influences separation based on interactions with analytes.
Column Dimensions:
Length, diameter, and film thickness impact efficiency and retention times.