User`s guide

Method Development
210
time but may be required for the analysis of thermally labile
analytes.
Trap High Temperature—The trap is heated to the high
temperature at the selected rate. This is the secondary desorption
temperature. Set the trap high temperature so that even the heaviest
compounds will be moved from the trap onto the GC column.
During the heating and high temperature hold time, you need rapid
sample transfer without sample or sorbent degradation.
An effective way to ensure you have complete tube desorption is to
repeat an analysis of the same tube. Use the same method. If any
compounds are detected on the second run it is likely that the tube
was not completely desorbed during the first run. If this is the case,
you must adjust the primary desorb temperature or time.
NOTE: A trap packed with Chromosorb 102 should not exceed
250°C. A trap packed with charcoal or unsilanized glass
wool can be desorbed at 400°C.
NOTE: The trap temperature should not exceed the maximum
temperature of the adsorbent.
Transfer Line Temperature—The transfer line temperature should
be high enough to prevent condensation. For best reproducibility, set
the transfer line temperatures to 255°C or a value 5-10°C higher than
the temperature of the heated valve temperature. The transfer line
may be heated to between 50 and 300°C.
Heated Valve Temperature—The heated valve is a 4-port rotary
valve and is used to direct the carrier gas flow to the cold trap during
the desorption process, or to isolate the cold trap during tube
conditioning.
The heated valve and its associated pneumatic connections may be
heated to between 150 °C and 300 °C using the standard valve rotor
supplied with the TD.
Timing Tab
In order to minimize analysis times and optimize sample throughput,
the gas flow rates and temperatures are invariably adjusted to speed
up desorption and reduce the primary desorption time. Owing to the