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Teledyne API – Model T700 Dynamic Dilution Calibrator
4.2.3. GENERATE GPT: PERFORMING A GAS PHASE TITRATION
CALIBRATION
4.2.3.1. GPT Theory
4.2.3.2. Choosing an Input Concentration for the NO
06873B DCN6388
The principle of GPT is based on the rapid gas phase reaction between NO and O
which produces quantities of NO
NO
O
3
It has been empirically determined that under controlled circumstances the NO-O
reaction is very efficient (<1% residual O
from the mixing of NO and O
following conditions are met:
The amount of O
used in the mixture is known.
3
The amount of NO used in the mixture is AT LEAST 10% greater than the amount
O
in the mixture.
3
The volume of the mixing chamber is known.
The NO and O
flow rates (from which the time the two gases are in the mixing
3
chamber) are low enough to give a residence time of the reactants in the mixing
chamber of >2.75 ppm min.
Given the above conditions, the amount of NO
to (at a 1:1 ratio) to the amount of O
Since the O
flow rate of the T700's O
3
0.105 LPM) and the GPT chamber's volume is known, once the TOTAL GAS FLOW
requirements, the source concentration of NO, and the target concentration for the O
generator are entered into the calibrator's software. The T700 adjusts the NO flow rate
and diluent (zero air) flow rate to create the appropriate NO
It is important to ensure that there is enough NO in the GPT chamber to use up all of the
O
. Excess O
will react with the resulting NO
3
3
undetectable by most NO
The EPA requires that the NO content of a GPT mixture be at least 10% higher than the
O
content. Since there is no negative effect to having too much NO in the GPT
3
chamber, Teledyne API recommends that the NO concentration be chosen to be some
value higher (as much as twice as high) as the highest intended target NO
kept constant.
As long as the flow rate is also kept constant three of the four conditions listed in
Section 4.2.3.1 above are therefore constant and the NO
reliably varied by simply changing the O
EXAMPLE:
Calibration values of NO
The NO gas input concentration should be no lower than 495 ppb and can be
as high as 900 ppb.
Overview of Operating Modes and Basic Operation
as shown by the following equation:
2
NO
O
h
2
2
), therefore the concentration of NO
3
can be precisely predicted and controlled as long as the
3
2
added.
3
generator is a set fixed value (typically about
3
analyzers, this will result in false low readings.
x
concentration.
3
from 200 ppb to 450 ppb will be needed.
2
(
)
light
being output by the T700 will be equal
concentration at the output.
2
to produce NO
. Since NO
2
3
output can be easily and
2
,
3
Equation 4-4
3
resulting
2
3
is
3
value and
2
109
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