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Gas phase titration (gpt), Gpt principle of operation, Gpt calibrator check procedure – Teledyne 9110EH - Nitrogen Oxides Analyzer User Manual

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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