User`s guide

Method Development
214
If you have enabled this option, then you must enter a Standard
Inject time on the Timing tab. The standard addition valve is
activated for the duration of the standard injection time to allow
introduction of a volume of standard onto the sampling/desorption
end of the tube. After the end of the standard injection time, the
valve is closed and the ATD/TD will proceed with desorption of the
tube.
The internal standard should be a light gas or gas mixture, which is
typically not present in the sample. Deuterated compounds are ideal
surrogates.
The pressure (and temperature) of the sample loop should be
identical from run to run in order to transfer the same mass in each
case. In practice this means that you should have the exit of the loop
at or as close to atmospheric pressure as possible to ensure
repeatability.
The pressure must be adequate to reach the required setpoint.
Inlet Split and Outlet Split Options—Two split points are provided
in the TD: one before and one after the cold trap. By using either,
one, or both together, it is possible to set split ratios ranging from
zero to 100,000:1, enabling the ATD/TD to handle sample
concentrations ranging from part-per-trillion (ppt) to high percentage
levels.
The split point on the inlet to the cold trap also facilitates thermal
desorption analysis of samples with a high moisture content, by
reducing the amount of water entering the cold trap.
If you enable the inlet and/or the outlet split options, you must set the
split flow rates using the Adjust Split option on the Tools menu or
the features on the Pneumatics tab.
Operation of the multiple splitter is covered in detail in Setting
Sample Split Ratios on page 228.
Heated Purge—Normally the sample is purged of residual air at
ambient temperature. If you enabled the heated purge option, the
tube will be heated as it is purged. This option can be used to remove
moisture and low boiling extraction solvents from the sample tube.
The temperature must be set so that moisture is removed from the