Inficon Transpector MPH, Руководство по эксплуатации

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Transpector MPH Operating Manual
The proportionality constant, K
ab
, depends on the nature of the substance being
detected and on the characteristics of Transpector MPH. The substance
dependent part is called the material factor,
M
ab
. The instrument dependent part is
called the analyzer factor, A
b
, and depends primarily on the ion mass, b . Therefore,
the original equation [1] can therefore, be rewritten as follows:
[2]
The material factor, M
ab
, depends on the fragmentation pattern for the particular
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
equation [3] :
[3]
FF
ab
is the fragmentation factor for substance
a
at mass
b
. It is equal to the fraction
of the total current of all ions from substance
a
which have a mass
b
.
XF
a
is the
ionization probability of substance
a
, relative to nitrogen (i.e.,
XF
N
=1
). That is, it is
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
Chapter 8 . Other valuable references include the Index
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 lists the fragmentation factors ( FF ) for the major peaks for selected
substances.
NOTE: Actual fragmentation factors vary significantly depending especially on the
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
PP
a
M
ab
A
b
  
I
ab

=
M
ab
1
FF
ab
XF
a

----------------------------- =