Teledyne 9110T instruction manual GAS Phase Titration GPT, GPT Principle of Operation, Equation

Model 9110T NOx Analyzer EPA Protocol Calibration

To provide for documentation and accountability of activities, a checklist should be compiled and then filled out by the field operator as each activity is completed.

For information on shelter and sample inlet system, an in-depth study is in Field Operations Guide for Automatic Air Monitoring Equipment, Publication No. APTD-0736, PB 202-249 and PB 204-650, U.S. Environmental Protection Agency, Office of Air Programs, October 1972

10.5. GAS PHASE TITRATION (GPT)

10.5.1. GPT PRINCIPLE OF OPERATION

Gas phase titration (GPT) is recommended during calibration of the 9110T. Those using a NO2 permeation tube should refer to the CFR1.

The principle of GPT is based on the rapid gas phase reaction between NO and O3 that produces stoichiometric quantities of NO2 as shown by the following equation:

Equation 10-1

NO+ O3 ⎯⎯→NO2 + O2 + hν

∙Given that the O3 concentration is known for this reaction, the resultant concentration of NO2 can be determined. Ozone is added to excess NO in a dynamic calibration system as shown in Figure 10-1, and the NO channel of the chemiluminescence analyzer detects the changes in NO concentration.

∙After the addition of O3, the observed decrease in NO concentration on the calibrated NO channel is equivalent to the concentration of NO2 produced.

∙The amount of generated NO2 may be varied by adding varying amounts of O3 from a stable O3 generator.

∙All zero air used in this procedure should conform to the requirements stated in Section 10.2 .

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 CFR1.

10.5.2. GPT CALIBRATOR CHECK PROCEDURE

It has been empirically determined that the NO-O3reaction is complete (<1% residual O3) 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 Register1. 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 Equation 10-6 and Equation 10-7 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.

1.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 SRM, as discussed in the Q.A. Handbook.

Teledyne Analytical Instruments 225