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Teledyne API – Model T700 Dynamic Dilution Calibrator Principles of Operation
275
10.1.1. GAS PHASE TITRATION MIXTURES FOR O3 AND NO2
Because ozone is a very reactive and therefore under normal ambient conditions a short-
lived gas, it cannot be reliably bottled, however, an optional O
3
generator can be
included in the T700 calibrator that allows the instrument to be use to create calibration
mixtures that include O
3
.
This ability to generate O
3
internally also allows the T700 Dynamic Dilution Calibrator
to be used to create calibration mixture containing NO
2
using a gas phase titration
process (GPT) by precisely mixing bottled NO of a known concentration with O
3
of a
known n concentration and diluent gas (zero air).
The principle of GPT is based on the rapid gas phase reaction between NO and O
3
that
produces quantities of NO
2
as according to the following equation:
Equation 10-3
)(
223
lighthONOONO
Under controlled circumstances, the NO-O
3
reaction is very efficient (<1% residual O
3
),
therefore the concentration of NO
2
resulting from the mixing of NO and O
3
can be
accurately predicted and controlled as long as the following conditions are met:
The amount of O
3
used in the mixture is known.
The amount of NO used in the mixture is AT LEAST 10% greater than the amount
O
3
in the mixture.
The volume of the mixing chamber is known.
The NO and O
3
flow rates (from which the time the two gases are in the mixing
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
2
being output by the T700 will be equal
to (at a 1:1 ratio) the amount of O
3
added.
Since:
The O
3
flow rate of the T700’s O
3
generator is a fixed value (typically about 0.105
LPM);
The GPT chamber’s volume is known,
The source concentration of NO is a fixed value,
Once the TOTALFLOW is determined and entered into the T700’s memory and target
concentration for the O
3
generator are entered into the calibrator’s software, the T700
adjusts the NO flow rate and diluent (zero air) flow rate to precisely create the
appropriate NO
2
concentration at the output.
06873B DCN6388