Tcd Troubleshooting; Sensitivity; Baseline Drift; Negative Peaks - Thermo Scientific TRACE GC Ultra Maintenance And Troubleshooting Manual

TCD Troubleshooting

TCD Troubleshooting

Sensitivity

Sensitivity is related to the detector temperature (increasing temperature reduce
sensitivity) and to the flow rate of the carrier, reference and make-up gas. A gain
in sensitivity can be obtained increasing the gap between the temperature of the
block and that of the filaments or increasing the filaments voltage.
Sensitivity is strictly related to the state of the filaments and to their operating
conditions. A significant reduction of the detector sensitivity may be caused by
the contamination of the filaments due to degradation of high molecular weight
compounds inside the cell or to contaminated gases.
Low temperatures of the detector block may cause high boiling compounds
condensate on the filaments reducing sensitivity.

Baseline drift

A small baseline drift normally occurs during a temperature program and does not
indicate a trouble. This effect is due to the decrease of the carrier gas flow rate as
temperature increases.
A baseline that suddenly goes out of scale and a rapid growth of the signal could
indicate that filaments are likely to be burnt and have to be replaced.

Negative peaks

Negative peaks are normally generated by the sample components that have a
thermal conductivity higher than carrier gas. For instance, using nitrogen or argon
as carrier gas, negative peaks are obtained for helium, hydrogen or methane.
To revert the polarity of the detector, refer to the TRACE
Manual for instructions.
Maintenance and Troubleshooting Manual
Maintaining a Thermal Conductivity Detector
TM
GC Ultra Operating
Chapter 16
341