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Teledyne API Model 200AU NO
X
Analyzer Instruction Manual, 02293, Rev. F
7-12
Selection of NO span gas standards
The NIST-SRM's provide references against which all calibration gas mixtures must be
compared (Section 2.0.7, Q.A. Handbook). The procedure requires the comparison of the
concentration of a commercial, working calibration standard to an NIST-SRM. This is described
in Subsection 7.1 of Section 2.0.7, Q.A. Handbook. Subsections 7.1.4 and 7.1.5 describe the
verification and re-analysis of cylinder gases.
Care must be taken to assure that no oxygen is allowed in the NO tank, regulator, or sample
lines. If oxygen is present, it reacts with NO to produce NO
2
, which can lead to significant errors
in NO concentration measurement.
It is good practice to request a NO
x
analysis from the supplier of the NO calibration gas.
Generally the maximum NO
2
impurity that should be allowed is 1% of the NO concentration.
The NO
2
impurity in the NO standard can be measured by the M200AU. A procedure is given in
the TAD for NO
2
measurement.
Use of NO
2
permeation tubes as standards
The steps required to compare the concentration of a commercial working calibration standard to
an NIST-SRM are described in Subsection 7.3.3 of Section 2.0.7, Q.A. Handbook. See
Subsection 7.3.6 for the re-analysis of permeation tubes.
7.6.3 Data Recording Device
Either a strip chart recorder, data acquisition system, digital data acquisition system should be
used to record the data from the M200AU RS-232 port or analog outputs. If analog readings are
being used, the response of that system should be checked against a NIST referenced voltage
source or meter. Data recording device should be capable of bi-polar operation so that negative
readings can be recorded.
7.6.4 Gas Phase Titration (GPT) System
7.6.4.1 Gas Phase Titration (GPT
Gas Phase Titration (GPT) with serial dilution is recommended for checking the converter
efficiency and NO
2
channel linearity of the M200AU. Those using a NO
2
permeation tube
should refer to TAD.
2
The principle of GPT is based on the rapid gas phase reaction between NO and O
3
which
produces stoichiometric quantities of NO
2
as shown by the following equation:
223
ONOONO
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