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6.0
PURIFICATION REACTORS
6.1
AADCO Instruments offers four basic types of purification reactors, designated "A",
"B", "C", and "D".
6.2
The "A" PURIFICATION REACTOR produces air of purity outlined in Section 8.0
and with an oxygen concentration of 20.8% ± 0.3%. In addition, the C0
concentration will be that of the ambient environment of the user's locale (~350-
ppm). This purification reactor should be specified if the operator wishes to avoid
calibration disparities where it is essential that the C0
and the sample be the same; e.g., use of the flame photometric detector or NDIR.
The "A" model is the most universal purification reactor and is usually supplied
when advised of this application. It is the reactor to be employed for air monitoring.
6.3
The "B" PURIFICATION REACTOR is factory set to produce air with the same
purity as the "A" model but with an oxygen concentration of 37.0% ± 0.5%, at
specified conditions. By in-house experimentation, this concentration has been
found to produce a greatly increased response for most commercial flame
ionization detectors over that response experienced with cylinder air. This has
since been field proven and has become the purification reactor of choice when
high sensitivity FID is required. It has also been found to decrease the noise level
of the flame photometric detector when used in conjunction in a chromatography
mode. Use of this purification reactor will eliminate both the oxygen and air
cylinders when operating this detector for that application.
6.4
It should be noted that output flows less than 50% of the rated output should be
avoided with any model pure air generator which contains a "B" reactor. This is the
lower threshold for maintaining the oxygen output at 37%. Flows below this level
will produce an oxygen enrichment greater than 37% oxygen. This higher oxygen
level causes the flame to become too hot with a consequent increase in noise. This
increased noise can be nullified, without loss of sensitivity, by decreasing the
hydrogen flow slightly.
6.5
Those chromatographers actively using flame ionization detectors with pure air
generators having "B" reactors experience a response from three to ten times
greater than the response of the same detector with cylinder air, particularly if
nitrogen is used as the carrier gas. The magnitude of this increased response will
depend upon the particular detector. The substitution of nitrogen for helium carrier
gas will also improve resolution within the GC column. The more dense the carrier
gas the better the resolution.
level for both the "zero" air
2
2
12
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