Gas Chromatography - GC Detectors > The Katherometer Detector > Page 45
The Katherometer Detector
The katherometer detector (sometimes spelt catherometer and often referred to as the thermal conductivity detector or hot wire detector) is relatively insensitive but has survived largely as a result of its catholic response and, in particular, its response to the permanent gases. Consequently, it is often the detector of choice for gas analysis and environmental testing. Its frequent use in these special types of application, somewhat surprisingly, has made it the fourth most commonly used GC detector. A filament carrying a current is situated in the column eluent and, under equilibrium conditions, the heat generated in the filament is equal to the heat lost by conduction and convection and consequently the filament assumes a constant temperature. At the equilibrium temperature, the resistance of the filament and thus the potential across it is also constant.
Figure 29. The Katherometer Detector ("In-Line Cell")
The heat lost from the filament will depend on the thermal conductivity of the gas and its specific heat and both these parameters will change in the presence of a foreign gas or solute vapor. The presence of a different gas entering the detector causes the equilibrium temperature to change, producing a change in potential across the filament. This potential change is amplified and fed to a suitable recorder. A diagram of the katherometer is shown in figure 29.