Inficon Transpector XPR 3+, Operating Manual, Page: 78 / 130

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Transpector XPR 3+ Operating Manual
4.1.3.3 Fragmentation Factors
The fragmentation factor is the fraction of the total ion current contributed by ions
of the chosen mass. Only peaks contributing at least one percent to the total ion
current are included in the list. The sum of the factors for all the peaks in a mass
spectrum cannot exceed 1.00. The sum can be less than 1.00 if only some of the
peaks are listed (either there are many peaks, or some of the ions produced lie
outside the mass range of the particular instrument used).
The data presented earlier in Table 4-4 on page 4-11 , Typical fragmentation factors
for the major peaks of some common substances , is compiled from more than one
source and is for illustrative purposes only. For maximum accuracy in determining
partial pressures, the fragmentation factors for the substances of interest should be
measured with the same instrument, and the same adjustments, as the samples to
be analyzed.
4.1.3.4 High Pressure Effects
As described in Section 3.7, High Pressure Effects, on page 3-11 , when
approaching the high pressure limit of operation the ion current does not increase
linearly with pressure because of ion losses that are pressure dependent. The
degree of ion loss depends on the nature of the ion in question and the nature of
the total gas environment in the sensor. If conditions are sufficiently defined, i.e. the
type of major gases and the interaction with the ion of interest, it is possible to
compensate mathematically for the non-linear behavior at the high pressure end of
the range. Transpector XPR 3+ permits the user to make such a compensation
using the total pressure sensed by the ion source and an empirically determined
factor for specific gases. Even when the exact factor is not known, the
compensated results are typically more nearly accurate than the raw data.