Calibration
Equipment Required
4-4
Model 42
i
Trace Level Instruction Manual
Thermo Fisher Scientific
Note
Ozone generators of the electric discharge type may produce NO and
NO
2
and are not recommended.
▲
A valve can be used to divert the NO flow when zero air is required at the
manifold.
The reaction chamber used for the reaction of ozone with excess NO
should have sufficient volume so that the residence time meets the
requirements specified in this chapter.
The mixing chamber is used to provide thorough mixing of the reaction
products and diluent air.
The output manifold should be of sufficient diameter to insure an
insignificant pressure drop at the analyzer connection. The system must
have a vent designed to insure atmospheric pressure at the manifold and to
prevent ambient air from entering the manifold.
The following information describes the NO concentration standard and
the method for calculating the NO concentration standard and the NO
2
impurity.
A cylinder containing 10 to 50 ppm NO in N
2
with less than 1 ppm NO
2
is usually used as the concentration standard. The cylinder must be
traceable to a National Institute of Standards and Technology (NIST) NO
in N
2
Standard Reference Material or NO
2
Standard Reference Material.
Procedures for certifying the NO cylinder (working standard) against an
NIST traceable NO or NO
2
standard and for determining the amount of
NO
2
impurity are given in EPA Publication No. EPA-600/4-75-003,
“Technical Assistance Document for the Chemiluminescence Measurement
of Nitrogen Dioxide.”
In addition, the procedure for the certification of a NO working standard
against an NIST traceable NO standard and determination of the amount
of NO
2
impurity in the working standard is reproduced here. The cylinder
should be re-certified on a regular basis as determined by the local quality
control program.
Diverter Valve
Reaction Chamber
Mixing Chamber
Output Manifold
Reagents
NO Concentration Standard
