Gas Chromatography

A gas chromatography technique involves a heated inlet, separate column, automated oven and a transfer line to deliver the sample to the mass spectrometry. The compound which I extracted is injected inside the GC heat inlet, from where it is vaporized and transferred via separating column into the detector. The GC then divides the compound while they are in gaseous phase via helium gas and the liquid phase which is inside the separating column. According to the different types of drugs and GCs, many different liquid stationary phases and their separating columns are available. The gas phase substances move inside and outside the stationary phase depending on the structure of their chemicals while they are being carried to the detector. Inside the GC oven, separating column can either be held isothermally or it can be ramped to high temperature. This enables a pure compound to be delivered to the detector. Conventional detectors in GC include FID – Flame Ionization Detectors, TCD – Thermal Conductivity Detectors, ECD, NPD and MS.

Many separating columns for MS are glass made or metal quartz made capillary columns which vary from 20 to 200 meters with diameters of 50 to 500 micrometers. The column’s inner wall has the liquid stationary phase coated to it which varies from 0.18 to 0.53 mm. many kinds of stationary phases are available in the markets such as hydrophobic, hydrophilic, non polar or polar. The type of stationary phase utilized depends on the chemical composition of the compound that is to be detected. Capillary columns can utilize flow rates which are lower such as 1 to 4 mL/min which are good for MS systems as they can run quite efficiently in high vacuum. Flow rate which exceeds the vacuum capacity of MS system, which is greater than 2 mL/min for diffusion pump or more than 4 mL/min when using a turbo pump, can increase the noise and reduce the test’s sensitivity.

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