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Tuesday, May 21, 2019

Factors affecting retention time in gas chromatography

The GC is a potent analytical technique of separation of volatile components, separation of the analytes depends on the interaction strengths of each compound with the stationary phase. Each component is separated from the column having a specific retention time (RT), the Retention time of a compound depends on several factors such as conditions of the analysis, temperature, and type of column used, dimensions of the column, and degradation of the sample, etc. Here are mentioned some factors affecting the retention time in GC.
The volatility of the component:
Compared to non-volatile components, the volatile component travels rapidly through the GC column. The volatility is related to the size and boiling point of molecules. This means that smaller size molecules have short RT as compared to the larger molecules.
The polarity of the component:
The polarity of compounds is associated with the polarity of the stationary phase. When the stationary phase and the polarity of the compound are parallel, the RT increases. This happens as the compound has more interaction with a stationary phase.  The amount of sample injected:
The amount of the sample does not affect retention time. If the sample is injected in high quantity, then the peak shows a tailing rather than asymmetrical shape.
The amount of stationary phase:
The Retention factor (k value) of the analytes is associated with the amount of stationary phase. If the more stationary phase exists, the retention factor is larger and thus the retention time will be more.
The column length:
A longer length of column usually increases the retention times as well as it improves the separation.
The column temperature:
The high temperature of the GC column is the result of low retention time with poor separation.
Flow rate and type of carrier gas:
Hydrogen gas gives a short time of analysis, as compared to other carrier gases (Helium) used in the gas chromatography. A high flow rate can also reduce the retention time of the component.
 

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