Sharp JX-9400 Informations techniques Page 156

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Item 5 is important mainly if the concentration is relatively high (for example,
0.1 per cent or higher). For this reason and to achieve also items 3, 4 and 7,
items 1 and 2 are essential.
Table 7.2 shows properties of tracers that have been used, together with
appropriate detection methods. Note that the mass spectrometer (MS) can
Table 7.2 Properties of the gases most frequently used as tracers
Tracer name Chemical
formula
Molecular
weight
Density/air
@NTP
MAC
[ppm]
MDCy
[]
Analyser
(besides
MS)
Helium He 4 0.14 >6 10
6
Neon Ne 20 0.69 >20 10
12
Carbon dioxide CO
2
44 1.53 5000 3 10
6
IR
Nitrous oxide N
2
O 44 1.53 25 50 10
9
IR
Sulphur hexafluoride SF
6
146 5.10 1000 0:1 10
12
ECD (IR)
Freon R11 CFCl
3
137 4.74 1000 1 10
12
ECD (IR)
Freon R12 CF
2
Cl
2
120 4.17 1000 50 10
9
ECD (IR)
Freon R13 CF
3
Cl 104 3.60 1000 50 10
9
ECD (IR)
Freon R22 CHF
2
Cl 86 2.99 1000 20 10
9
ECD (IR)
Freon R111 CCl
3
–CCl
2
F 220 7.60 1000 ECD (IR)
Freon R112 CCl
2
F–CCl
2
F 203 7.03 1000 50 10
9
ECD (IR)
Freon R113 CCl
2
F–CClF
2
187 5.90 1000 50 10
9
ECD (IR)
Freon R114 CClF
2
CClF
2
171 5.90 1000 50 10
9
ECD (IR)
Freon R115 CClF
2
CF
3
154 5.31 1000 ECD (IR)
Halon 1211 CF
2
BrCl 165 5.53 ? 0:5 10
9
ECD (IR)
Halon 1301 CF
3
Br 149 4.99 ? 10 10
12
ECD (IR)
Perfreons
Liquid @NTP
PB C
6
F
6
186 (6.4) ECD
Perfreobenzene
PMB CF
3
C
6
F
5
236 (8.1) ECD
Perfluoromethylbenzene
PMCH CF
3
C
6
F
11
350 (12.1) 10
14
ECD
Perfluoro-methyl-cyclohexane
PDCH CF
3
CF
3
C
6
F
10
400 (13.8) 10
14
ECD
Perfluoro-dimethyl-cyclohexane
PMCP CF
3
C
5
F
9
300 (10.3) 10
14
ECD
Perfluoro-methyl-cyclopentane
PDCB CF
3
CF
3
C
4
F
6
300 (10.3) 10
14
ECD
Perfluoro-dimethyl-cyclobutane
Note:
MAC ¼maximum acceptable concentration for health safety; yMDC ¼minimum
detectable concentration using the best available analyser. The useful concentration is about 100
times larger; IR: Infrared absorption spectrograph or photo-acoustic detector; ECD: Gas
chromatography and electron capture detector.
Common Methods and Techniques 135
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