Often, the columns are capillary tubes that are coated with a silicone based oil that absorbs the chemicals within the gas passing through. Chemicals within the sample will be absorbed by the column at different rates and are eluted at different temperatures, therefore different compounds within the sample can be separated. Unlike other types of chromatography, GC columns are typically very long, a 100 meters or more. There are many different types of detectors for a GC instruments.
Flame ionizing detectors (FID) are most commonly used. FIDs use hydrogen to create a flame at the end of the chromatography column between two electrodes. The flame breaks any up any organic compounds and hydrocarbons through a process call pyrolysis. Carbon atoms forms cations which can be detected by the electrodes. Thermal conductivity detectors (TCD) are also common and are non-destructive so they are usually incorporated before an FID. TCDs work by determining the conductivity of gas passing electricity to a tungsten -rhenium filament.
The carrier gas typically has high thermal conductivity but during elution the molecules within the sample often are less conductive which can be measured as a voltage drop at the filament. Mass spectrometer detector are also common.
0 kommentar(er)
