Hydrocarbon analyzer, Flame ionization and Thermal conductivity detector method


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Gaseous hydrocarbons can be reactive or non-reactive ethylene and methane is the examples for reactive and non-reactive gases respectively. Methane is the major hydrocarbon emitted to the atmosphere by natural activities such as anaerobic decomposition in water and solid.

The poly Aromatic Hydrocarbons (PAH) can be analyzed by collecting them with glass fiber filters. PAH can be extracted from benzene and then it is analyzed by Flame ionization detector.

Flame Ionization Detectors:

FIDs are best for detecting hydrocarbons and other easily flammable components. They are very sensitive to these components, and the response tends to be linear across a wide range of concentrations.

The sensor is the burner in which the regulated flow of sample gas passes through a flame sustained by the regulated flow of fuel gas and air.

Within the flame, the hydrocarbon components of the sample stream undergo a complex ionisation that produces an electron and positive ions. Polarized electrons collect these ions, causing current to flow through the electronic measuring circuitry.

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Current flow is proportional to the rate at which carbon atoms enter the burner. The sample fuel passes through the burner jet and into the flame. The air stream flows around the periphery of the flame. The burner jet and the collector functions as electrodes.

The field causes the charged particle formed during combustion to migrate. The electron goes to burner jet; positive ions go to the collector. Thus a small ionization current flows between the two electrodes. The magnitude of the current depends on the concentration of the carbon atom in the sample.

Thermal conductivity detector (TCD):

The thermal conductivity detector (TCD) is a bulk property detector and a chemical specific detector commonly used in gas-liquid chromatography.

TCD

TCD consists of an electrically heated filament in a temperature-controlled cell. Under normal conditions, there is a stable heat flow from the filament to the detector body. When an analyte elutes and the thermal conductivity of the column effluent is reduced, the filament heats up and changes resistance.

This resistance change is often sensed by a Wheatstone bridge circuit which produces a measurable voltage change. The column effluent flows over one of the resistors while the reference flow is over a second resistor in the four-resistor circuit