Inficon Transpector MPH Operating Manual page 74

The proportionality constant, K
detected and on the characteristics of Transpector MPH. The substance
dependent part is called the material factor, M
called the analyzer factor, A
the original
PP =
a
The material factor, M
substance, the fragmentation pattern for a reference gas (usually nitrogen), and the
ease with which the substance can be ionized relative to the same reference gas.
The relationship involved is shown in
M
ab
FF is the fragmentation factor for substance a at mass b. It is equal to the fraction
ab
of the total current of all ions from substance a which have a mass b. XF
ionization probability of substance a, relative to nitrogen (i.e., XF
the ratio of total ion current (for all masses) from substance a to the total ion current
from nitrogen, both measured at the same true partial pressure. Both fragmentation
factors and ionization probabilities depend strongly on the energy of the ionizing
electrons. If the correct values of these factors are not known for the exact
conditions of the particular analyzer being used, they can be approximated using
published values for other conditions with, generally, only a small loss in accuracy.
Fragmentation factors can be calculated from fragmentation patterns given in the
general references cited in
of Mass Spectral Data from ASTM, EPA/NIH Mass Spectral Data Base by Heller
and Milne, and an extensive library of spectra available from the National Institute
of Standards and Technology.
Table 4-4
substances.
NOTE: Actual fragmentation factors vary significantly depending especially on the
4 - 9
b
equation [1] can therefore, be rewritten as follows:
   
M A I
ab b ab
, depends on the fragmentation pattern for the particular
ab
1
= ---------------------------- -

FF XF
ab a
Chapter
lists the fragmentation factors (FF) for the major peaks for selected
ionizer, electron energy, and mass filter turning. For best accuracy,
measure fragmentation factors with the same instrument used for the
analysis, under the same tuning conditions
, depends on the nature of the substance being
ab
. The instrument dependent part is
ab
, and depends primarily on the ion mass, b. Therefore,
equation [3]:
8. Other valuable references include the Index
Transpector MPH Operating Manual
a
=1). That is, it is
N
[2]
[3]
is the