VICI TCD2 - Manual (Page 19)

15
Installation
Initial Power-Up
Since the TCD is a concentration-dependent detector, the lower the flow
rate through the detector, the higher the sensitivity. Column diameter will
determine the optimum column flow rate.
The microvolume TCD is designed for the lower flow rates typical for capillary
columns, and achieves best sensitivity at rates below 10 ml/min. Since the
filaments are maintained at constant temperature, the detector can be
operated at extremely low flow rates (less than 0.5 ml/min) without damage
to the filaments.
A - B referenced mode
Flow Rate Settings
1. Measure the column flow at the detector’s Channel A out. The optimum
flow rate is in the range of 4 - 20 mL/min, with the actual rate dependent
on the type of column used.
2. Measure the reference gas flow at Channel B out. It should be as close as
possible to the GC column flow. Use a fixed flow restrictor or a good
quality flow controller to match the the carrier gas and reference gas flows.
3. Once the flows have been established, make sure the filament switch and
the main power switch are in the OFF position, and plug the power cord
into an AC main outlet.
Initial Conditioning
4. Turn on the control module main power switch and set the detector
temperature to 220°C.
5. Turn on the filament power switch and set both filament temperature knobs
at 8.0.
6. Condition the detector by allowing it to bake at these settings for at least
12 hours.
Temperature Settings
7. After the initial bakeout period, set the detector temperature at 100°C or at
the column temperature plus 30°, whichever is higher.
8. Set the filament temperatures at least 50° and as much as 100° higher
than the detector temperature. Refer to Figure 3 on page 5, which
outlines the relationship between the filament temperature knob settings
and the actual filament temperature.
Detector sensitivity increases as the temperature differential between the
detector and the filaments increases, but filament life decreases as its
temperature increases. Thus, the detector temperature should be set as
low as possible, determined by the boiling point of the highest boiling
component of the sample.
9. Once all temperatures are set, allow plenty of time for the system to
equilibrate, evidenced by a stable baseline. Typical equilibration time for
going from a cold start-up to 130°C detector temperature is approximately
five hours. Detector temperature changes take much longer to equilibrate
than do filament temperature changes.