User`s guide

Method Development
215
tube, but not so high that the sample starts to come off the tube. If
sample starts to be desorbed it will be lost to vent during tube purge.
If you enable this option, you must also enter a suitable purge
temperature to the appropriate field on the Preferences tab. The
default setting is 50°C.
Heated purge takes place during dry purging. The minimum
temperature is 50°C. The tube oven will extend to contact the tube
during the purge phase, then retract to heat to the primary desorb
temperature, when it will again extend. No flow occurs during the
temperature transition phase.
Operating Modes—The ATD/TD can operate in one of five modes
of operation. Your application will determine the operating mode. A
basic overview of each mode is provided in Operating Modes on
page 107. A detailed description of each mode that includes flow
diagrams is provided in Chapter 8.
High Temperature Operation
The Valcon T (P/N M041-0077) rotor is intended for high
temperature operation. It is extremely inert and is intended for
operation between 150 and 300 °C. At temperatures below 150°C
there is a tendency for the seal material to stick to the valve body,
making the valve difficult to turn and causing the rotor to crack, in
extreme cases.
NOTE: The Valcon T rotor is composed of a polyimide/PTFE/
carbon composite. This material is susceptible to attack
from steam, ammonia, hydrazines (anhydrous liquids or
vapor), primary and secondary amines, and solutions
having a pH of 10 or more. Chemical reagents which act as
powerful oxidizing agents (nitric acid, nitrogen tetroxide,
etc.) must also be avoided.
1
Another consideration for high temperature operation is the o-rings
contained in the fixed seal of the tube handling system. Your
instrument is shipped with Viton o-rings (P/N L1003006 for.009 size
or L1003006 for.011 size). The Viton o-rings are intended to be used
at temperatures up to 225°C. Beyond this temperature they will
1. http://www.vici.com/ref/mat_rotr.htm#valtf