User`s guide

Method Development
213
The Options Tab
The Options tab provides further method options for your
application.
Number of Injections—This parameter specifies the number of
desorptions per sample tube. For example, If you enter 99 the first
selected tube will be loaded and will continue to go through
desorption cycle until you press Stop.
NOTE: However, if a value of 99 is entered for any of the methods
in a sequence, the sequence will stop after that method is
run and 99 injections have occurred.
If you take two consecutive samples from the same tube, the peak
area obtained for the second sample may be smaller than the area
obtained in the first analysis. If you continue taking successive
samples from the tube, the total amount of the analyte present will
further decline, eventually becoming totally exhausted. Thus, the
sum of the amounts of the analyte removed in the individual
extractions will be equal to the total amount of analyte present in the
original sample. The advantage is that by extracting the whole
amount of the analyte, any effect of the sample matrix is eliminated
and quantitative determination of the total amount present depends
only on the relationship (i.e. on the response factor value), just as in
any quantitative measurement by GC.
In practice, you will not carry out the extractions indefinitely: from a
limited number of consecutive extractions the peak area
corresponding to the total amount of analyte present is obtained by
extrapolation, based on mathematical relationships.
1
Standard Injection—If your ATD/TD is equipped with the optional
Internal Standard Addition accessory (P/N M041-3335) you can
enable or disable the option from this tab. A gaseous internal
standard can automatically be introduced onto every sample tube
prior to desorption. The standard is added after the tube is purged,
and is added to the sample collection end of the tube.
1. Bruno Kolb and Leslie S. Ettre, Static Headspace Gas
Chromatography, Theory and Practice, (New York, 1997), p. 40-41