As is the case with all detectors for gas chromatography, thermal control ofa FID is an important requirement. The block enclosing the detector should beheated above the temperature of the column to avoid the condensation of samplecomponents in the transfer lines and jet. In addition, the temperature must beabove 100 oC to prevent water condensation. Since the temperature of the bodyof the detector has a slight effect on the detection mechanism it must be stable.However, it is more important to keep the detector from getting too hot sincesolid surfaces heated by the flame can emit electrons (i.e., thermionic ionization).For example, a large sample or component that can increase the temperature cancause a positive detector response, including samples or components that otherwisewould have given a negligible response (e.g., CO). Under such conditions,water may give a negative peak, as it decreases the temperature of the flame.Overheating the detector can also lead to electrical leakage across insulators,causing instability in the detector output current.《Modern Practice of Gas Chromatography》