Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 147)

Model 9110EH Instruction Manual EPA Protocol Calibration
8.2. Gas Phase Titration (GPT)
8.2.1. GPT Principle of Operation
Gas phase titration (GPT) is recommended for calibration of the M200E. Those using a NO
2
permeation tube should refer to the CFR 1 .
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:
ν h O NO O NO + + →  +
2 2 3
Given that the O
3
concentration is known for this reaction, the resultant concentration of
NO
2
can be determined. Ozone is added to excess NO in a dynamic calibration system as
shown in Figure 8-1, and the NO channel of the chemiluminescence analyzer detects the
changes in NO concentration. After the addition of O
3
, the observed decrease in NO
concentration on the calibrated NO channel is equivalent to the concentration of NO
2
produced. The amount of generated NO
2
may be varied by adding varying amounts of O
3
from a stable O
3
generator. All zero air used in this procedure should conform to the
requirements stated in Section 8.1 of this manual.
Dynamic calibration systems based on this principle are commercially available, or may be
assembled by the user. A recommended calibration system is described in the Federal
Register 1 CFR 1 .
8.2.2. GPT Calibrator Check Procedure
It has been empirically determined that the NO-O
3
reaction is complete (<1% residual O
3
) if
the NO concentration in the reaction cell (ppm) multiplied by the residence time (min.) of
the reactants in the chamber is >2.75 ppm min. The theory behind the development of this
equation is in the Federal Register 1 . The following procedures and equations should be used
to determine whether an existing GPT calibration system will meet required conditions for a
specific calibration.
For calibrators that have known pre-set flow rates, use equations 8-5 and 8-6 of steps 7
and 8 (below) to verify the required conditions. If the calibrator does not meet
specifications, follow the complete procedure to determine what flow modifications must be
made.
Select an NO standard gas that has a nominal concentration in the range of 50 to 100 ppm.
Determine the exact concentration [NO]
STD
by referencing against an NIST-SRM, as
discussed in the Q.A. Handbook.
Determine the volume (cm 3 ) of the calibrator reaction cell (V
RC
). If the actual volume is not
known, estimate the volume by measuring the approximate dimensions of the chamber and
using an appropriate formula.
Determine the required minimum total flow output (F
T
) using Equation 8-1:
F
T
= analyzer flow demand (cm 3 /min) x 110/100 Eq 8-1
M9110EH Rev 0 133