5–30
Transpector CPM Operating Manual
The analyzer factor, A
b
, depends on the transmission and detection characteristics
of the analyzer, the EM gain (if the analyzer is so equipped), and the basic
sensitivity. (See equation [7].)
[7]
The transmission factor of the mass filter at mass (b) is (TF
b
). The transmission
factor is the fraction of ions at mass (b) which pass through the mass filter, relative
to nitrogen ions at mass 28. Nominally, the transmission factor is equal to 28
divided by the mass of the ion (b).
The detection factor (DF
ab
) is equal to 1 for a Faraday Cup detector. For an EM,
the detection factor is a function of the mass of the ion and its chemical nature, and
is measured relative to that of a reference gas, typically nitrogen. In general, as the
mass ion increases, the EM detection factor decreases.
The gain of the EM (G) measured at mass 28 for nitrogen, is the EM output current
divided by the Faraday mode output current, under otherwise identical conditions.
The multiplier gain is a strong function of the high voltage applied.
The sensitivity of the instrument (S) is the Faraday mode ion current from a given
pressure of pure nitrogen measured at mass 28, and is typically expressed in
A/Torr.
cyclohexane C
6
H
12
6.4 propane C
3
H
8
3.7
deuterium D
2
0.35 silver perchlorate AgClO
4
3.6
dichlorodifluormethane CCl
2
F
2
2.7 stannic iodide Snl
4
6.7
dichloromethane CH
2
Cl
2
7.8 sulfur dioxide SO
2
2.1
dintrobenzene C
6
H
4
(NO
2
)
2
7.8 sulfur hexafluoride SF
6
2.3
ethane C
2
H
6
2.6 toluene C
6
H
5
CH
3
6.8
ethanol C
2
H
5
OH 3.6 trinitrobenzene C
6
H
3
(NO
2
)
3
9.0
ethylene oxide (CH
2
)
2
O 2.5 water H
2
O1.0
helium He 0.14 xenon Xe 3.0
hexane C
6
H
14
6.6 xylene C
6
H
4
(CH
3
)
2
7.8
hydrogen H
2
0.44
Table 5-9 Ionization Probabilities For Some Common Substances (continued)
Substance Formula Relative
Ionization
Gauge
Sensitivity
Substance Formula Relative
Ionization
Gauge
Sensitivity
A
a
1
TF
b
DF
ab
G S
---------------------------------------------------
=
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