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Chemiluminescent Measurement of NO/NOx in Gas Analysers
The chemiluminescence method for gas analysis of oxides of nitrogen relies on the measurement of light produced by the gas-phase titration of nitric oxide and ozone.

gas analyzers
Series III





Here is how chemiluminescence works:

NO is a relatively unstable molecule which will oxidize to NO2 (especially) in the presence of O3 . This reaction produces a quantity of light for each NO molecule which is reacted.

This light can be measured using a photomultiplier tube or solid state device.

If the volumes of sample gas and excess ozone are carefully controlled, the light level in the reaction chamber is proportional th the concentration of NO in the gas sample.

The chemiluminescence reaction of NO to NO2:

NO + O3 ==> NO2+ O2 + hv

If the amount of ozone present is sufficient to react all of the nitric oxide, then the quantity of light produced by the reaction will be proportional to the concentration of nitric oxide in the gas sample.


The Series 400 Converters may be used to convert NOx or NH3 to NO for use with a variety of gas analyzers.

The NOXGEN is used to perform NOx converter efficiency testing

Product information is located here.

Enhancements to this technique:
The chemiluminescence technique may be used to measure total oxides of nitrogen (NOx) by passing the sample over a heated catalyst to reduce all oxides of nitrogen to NO. This is done within the instrument, just prior to the reaction chamber. Some instruments can perform the automatic switching of the catalyst in and out of the sample path so that the resulting signals may be compared to indirectly measure NO2. Variations of chemiluminescence have been used to perfom measurements of Ammonia (NH3):

NH3 + O2 ==> NO + H2O
4NH3 + 5O2 = 4NO + 6H2O
4NO + 4O3 -------->4NO2+4O2 + 4hv




Microprocessors in Gas Analyzers:

The wide availability of powerful, inexpensive microprocessor technology has enabled modern gas analyzers to evolve from limited, analog instruments to sophisticated data collection nodes. Appropriate measurement technologies may be incorporated as modules into a common user platform featuring industry standard communications, common user interface and many standardized components across analyzer types. The best examples of this approach include features like automatic self-monitoring and diagnostics, programmable calibration routines and independently configurable alarm levels. Serial communications, remote control and data collection enable the integration of more powerful and coherent CEMS, flexability of data collection, remote diagnostics and streamlined spare parts stocking.











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