User`s guide

Accessories
193
Principle of Operation
The reference gas pre-fills the 0.5-mL loop during the loop load
time. This has been set to 30 seconds, at the factory. The 30 seconds
is the default setting which you can change. After a tube has been
loaded into the desorption position and following the leak test and
tube purge, the internal standard gas valve is switched so that the
loop is in series with the sample tube. Carrier gas transfers the loop
contents to the back of the tube. After the addition of the internal
standard, the tube is desorbed and the analytes and standard are
transferred to the cold trap as usual.
The accessory is equipped with a solenoid valve, which shuts off the
flow of standard gas if instrument power is shut off.
Another operation mode option is available with the Internal
Standard accessory. In this mode an internal standard is loaded into a
tube but not analyzed. This reference method will allow you to load
the tube with the reference standard before using the tube to collect
sample. To select this mode, go to the Status/Options tab and select
from the Mode drop down menu, Load ISTD on Tube.
Operation of the IS Accessory
To use the Internal Standard accessory during a method or sequence
follow this procedure.
1. Open the Status/Options tab and check off the Internal
Standard Inject box. The Internal Standard Addition
accessory will be enabled. See The Options Tab on page
103.
2. Set up the IS Loop Load and IS Tube Load flow rates as
well as the Loop Equil time by following the procedures
listed in the Setting IS Flow Rates section below.
3. At the touch screen go to the Tools menu and select the
Preferences entry, then select the Config tab and the
Internal Standards button. A dialog box will appear with
the Loop Load entry box. Set the amount of time (in
minutes) for the Standard Loop Fill.
10XLoop Volume (mL) / Load Flow (mL/Min) = Time
(Min)