GC Detectors

Shown below is a schematic diagram of a thermal conductivity detector. This is one of a matched pair of cells. The sample cell takes the carrier gas as it elutes from the column. A source of carrier gas that bypasses the column passes through a reference cell.


Shown here is a schematic diagram of a flame ionization detector. The eluent from the column mixes with H2 and is burned in the presence of excess air. Combustion produces a flame containing electrons and the cation CHO+. Applying a potential between the flame tip and the collector results a current that is proportional to the concentration of cations in the flame.


Shown below is a schematic diagram of an electron capture detector. Electrons from the β-emitter move toward the anode, generating a standing current. When an analyte capable of capturing electrons passes through the detector—an analyte containing an electronegative element, such as chlorine, for example—the current decreases. The chromatogram, therefore, shows current measured as a function of time.


Block diagram of GC–MS. A three component mixture (A, B, C) enters the GC. When component A elutes from the column, it enters the MS ion source and ionizes to form the parent ion (A+) and several fragment ions (x+, y+, z+). The ions enter the mass analyzer, which separates them by their mass-to-charge ratio, providing the mass spectrum shown at the detector.


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