PN T900-014, Rev B
Functional Overview of the ta7000F Gas Purity Monitor
To achieve the specified performance, the ta7000F Monitor performs the pri-
mary functions described below.
Component
Function
Carrier Gas Purification
A Getter Purifier is included as integral component of the car-
rier gas flow path. Impurities are reduced to a level of less than
100 PPT.
Sample Introduction and
Component Separation
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.
Flame Ionization
Detection (FID)
Species eluting from the FID column set pass immediately into
the heated bed of ruthenium oxide (Ru
3
O
4
) and the flame detec-
tor. Within the ruthenium oxide bed, the general reaction occurs:
CO
x
+ (2+X)H
2
=> CH
4
+XH
2
O (vapor)
Where COx is an appropriate carbon-oxygen compound gas. For
carbon dioxide the equilibrium reaction is:
CO
x
+ 4H
2
=> CH
4
+2H
2
O (vapor)
The resulting methane is quantitatively determined by means of
flame ionization immediately downstream of the ruthenium ox-
ide bed. Methane and other simple hydrocarbons pass through
the methanizer unaffected. Within the flame ionization region
hydrocarbons are reduced via a series of reaction steps to CH+
ions and electrons prior to complete combustion into H
2
O and
CO
2
. The resultant electrons are collected to generate a current
signal. Higher hydrocarbons, those containing more than a
single carbon group, generate additional CH+ Ions in proportion
to the carbon number. As a result the theoretical sensitivity of
the flame ionization detector to non-methane hydrocarbons is
at least two times higher than methane.
Contamination of carrier gases with reactive compounds such as
sulfides, chlorides, and aromatics will irreversibly impair reactiv-
ity and will necessitate methanizer replacement. Care should be
taken to bypass the instrument if these compounds are present
in the sample gas stream.
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