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Tuesday, September 24, 2019

Factors affecting the resolution in gas chromatography



GC is a chromatographic technique of separation in which the gas (e.g. Nitrogen, Helium) used as a mobile phase. Gas chromatography is one of the most accepted techniques for separating and analyzing analytes, because of its high accuracy, reproducibility, resolution, speed, and low range of detection. GC can be useful for the separation of any volatile compound, hence it GC useful in the separation of many organic and inorganic compounds.
The factors that affect the resolution in the GC is mentioned here.
The temperature of the column:
The extremely high temperature of the column is the result in low RT and poor separation of the analytes, as all components are mainly in the gas phase. However, the analytes require interaction with the stationary phase to be separated.
Vapor pressure
The compounds boiling point is often associated with its polarity. If the boiling point of the compound is low, the higher the vapor pressure and the retention time are shorter since the compound will use more time in the gas phase.
The concentration and volume of the sample solution:
Generally, the peaks have an asymmetric shape. If the concentration and the volume of the sample solution are too high, there is a tailing in the peaks, which is the reason for poor separation. The detectors used in the GC are extremely sensitive and they don’t need much material to give a detectable signal. E.g. Flame Ionization Detector (FID), Mass Spectrometer (MS), Electrolytic Conductivity Detector (ELCD), Flame Photometric Detector (FPD), Photoionization Detector (PID) etc.
The flow rate of carrier gas:
A higher flow rate shortens the retention time, but a poor the separation will also be observed. Since the molecules have little or no time to interact with the stationary phase and are simply pushed through the column by the carrier gas.
The polarity of the stationary phase on the column and polarity of components:
If the polarity of the compound and the stationary phase are the same, the component's RT will increase since the strong interaction with the stationary phase. As a result, polar molecules have a longer retention time when using a polar stationary phase and shorter retention times when using non-polar polar stationary phase.
The length of the column used:
If you use a longer length of the column, then the retention time of the component will increase in proportion to the column length and a significant peak broadening will be seen. Generally, separation improves when long columns are used in the analysis.

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