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Functional Overview of the ta7000R Gas Purity Monitor
To achieve the specified performance, the ta7000R Monitor performs the pri-
mary functions described below.
Component
Carrier Gas Purification
Sample Introduction and
Component Separation
Reduction Gas Detector
1-2 | ta7000R Gas Purity Monitor
Function
A catalytic combustor is included as an integral component of
the Carrier gas flow path. Reactive impurities are reduced to a
level of less than 100 PPT.
Samples are introduced into the instrument via air actuated
gas sampling valves. Components of interest are separated in a
1/8-inch Column(s) inside a heated column oven.
Species eluting from the Reduction Gas Detector (RGD) column
set pass immediately into the heated bed of mercuric oxide
(HgO) and the photometric detector. Within the HgO bed, the
general reaction occurs:
X + HgO (solid) => XO + Hg (vapor)
Where X is any appropriate reducing gas. The resulting mer-
cury vapor is quantified by means of an ultraviolet photometer
located immediately downstream of the mercuric oxide bed. The
relative ease of measuring mercury vapor at low concentrations
lends the technique its inherent sensitivity.
For carbon monoxide and hydrogen, the equilibrium reactions
are as follows:
CO + HgO (solid) => CO
H
+ HgO (solid) => H
2
The hydrogen reaction undergoes approximately 20 % conver-
sion to mercury vapor in relation to carbon monoxide. Under
continuous operation, the effective life of the mercuric oxide
bed is approximately two years. Contamination of Carrier gases
with reactive compounds such as sulfides, chlorides, and aro-
matics will irreversibly impair reactivity and will necessitate bed
replacement. Care should be taken to bypass the instrument if
these compounds are present in the Sample gas stream.
High concentrations of hydrogen and carbon monoxide will use
up the active sites in the reaction bed faster than lower level
concentrations.
+ Hg (vapor)
2
O + Hg (vapor)
2
PN T900-013, Rev A
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