Gas Chromatography Detectors - The Katharometer Detector > Page 32

A filament carrying a current is situated in a tubular cavity through which flows the column eluent. Under equilibrium conditions, the heat generated in the filament is equal to the heat lost and consequently the filament assumes a constant temperature. The heat lost from the filament will depend on both the thermal conductivity of the gas and its specific heat. Both these parameters will change in the presence of a different gas or solute vapor and as a result the temperature of the filament changes, causing a change in potential across the filament. This potential change is amplified and either fed to a suitablerecorder or passed to an appropriate data acquisition system.As the detector filament is in thermal equilibrium with its surroundings and the device actually responds to the heat lost from the filament, the detector is extremely flow and pressure sensitive. Consequently, all katharometer detectors must be carefully thermostatted and must be fitted with reference cells to help compensate for changes in pressure or flow rate.



Figure 13. The Off-Line Katharometer Sensor