Instruction 0011-9026
Page 16
As a rule of thumb, background gases/vapors may be present in con centrations up to
1/2% by volume (5000 ppm) before they present a signi
fi
cant interference problem to
the CO
2
or O
2
FYRITE (20/21% ranges).
An exception exists with the action of ammonia on Oxygen FYRITE Fluid. Ammonia
neutralizes the acidic solution of chromous chloride, and therefore use of the O
2
FY-
RITE with even trace amounts of ammonia in the backgrounds is not advised unless
suitable
fi
lters are used.
Inert gases, even in concentrations approaching 100% by volume, do not interfere with
either the CO
2
or O
2
FYRITE. In general, interferences can be of a chemical (chemical
reaction initiated) or a mechanical nature, with resultant error, but are also given up
by the solution when the sample no longer contains the interfering substance. They
can therefore be compensated for by saturating the FYRITE solution with samples
containing the mechanical interferant as long as the background stays reasonably
constant. Usually 3 or 4 tests are suf
fi
cient to saturate FYRITE solution with the
mechanical interferant in question.
TYPICAL
TYPE
OF
APPROXIMATE
INTERFERENCE INTERFERENCE EFFECT
(CO
2
FYRITE)
All
Acid
Gases
Chemical 1:1
(SO
2
, H
2
S, Hydro-
cynanic
Acid,
Cyanogen,
etc.).
TYPICAL
TYPE
OF
APPROXIMATE
INTERFERENCE
INTERFERENCE
EFFECT
(O
2
FYRITE)
Acetone Chemical 1:1
Acetylene
Chemical 1:1
and
other
unsaturated
hydrocarbons
CO
2
Mechanical,
20%
CO
2
Can be zeroed out up
background
can
be
to
approximately
30%
zeroed
out
in
3
to
4
CO
2
background.
tests
if
background
remains
constant.
Ammonia
Chemical Ammonia
neutralizes
O
2
FYRITE solution
and
instrument
use
on
this
background
is
not
advised
unless
suit-
able
fi
lters are used.
Nitrous Oxide (N
2
O) Mechanical
-
-
-
