Thermo Scientific FOCUS GC, Instruction Manual

Page: 177 / 356

Chapter 9
Selecting TCD Operating Parameters Thermal Conductivity Detector (TCD)
Instruction Manual 177
Selecting TCD Operating Parameters
The TCD can be set to operate in constant temperature (CT) and constant voltage
(CV) modes.
WARNING! In case of TCD with the polyimide coated filaments, the maximum operating
temperature is 300 °C for the TCD cell and 320 °C for the filaments.
Using the CT Mode
For samples in concentrations not exceeding 10%, use the following values:
• detector temperature: 10 °C higher than the maximum column oven
temperature reached during the analysis
• filament temperature: 80–100 ºC above the detector temperature.
The CT mode provides the highest sensitivity and is suggested for trace analysis
(ppm). Since the temperature remains constant, this mode considerably increases
the filament life compared to other operating modes.
For samples in concentrations not exceeding 1%, use the following values:
• detector temperature: 10 °C higher than the maximum temperature reached by
the column oven during the analysis, but not higher than 300 ºC
• filament temperature: 120–150 ºC above the detector temperature
Using the CV Mode
For samples in concentrations of a wide percentage range (1–100%), use the
following values:
• detector temperature:10 °C higher than the maximum column oven
temperature reached during the analysis
• filament voltage: 5–7 V
In this operating mode, the detector response is linear up to the maximum
concentrations.