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Chemiluminescence Detector

The Chemiluminescence effect is used to measure the concentration of NO and NOX. A molecule can pass of the electronic ground state to an excited electronic state through energy absorption. The absorbed energy can be emitted in the transition to an energetically lower state again. This happens on the one hand in form of heat (non-radiative deactivation) and on the other by the emission of light (luminescence). Nitrogen oxides arise in particular during combustion, thats why this analysis method finds application in the exhaust gas measurement technology of power plants, in the automotive industry as well as in environmental technology.

The chemiluminescence principle

Chemiluminescence refers to light which is emitted after excitation of a molecule during a chemical reaction. It is being used in the analysis of nitrogen gases.
Nitrogen monoxide reacts with ozone to excited nitrogen dioxide.
The subsequently emitted light (proportional to the NO-concentration) is measured and amplified by a photomultiplier.
In order to analyse higher nitrogen oxides, they have to be reduced with a catalyst (NOX-converter) to nitrogen monoxide.

NO + O3 → NO2* + O2
NO2* → NO2 + hν (luminescence)

If all nitrogen oxides should be measured in a single sample gas stream, the content of nitrogen monoxide must be measured first. This measurement is carried out without the catalyst. Subsequently, the gas stream is passed over the catalyst and thus all nitrogen oxides (e.g. NO2) are reduced to NO. The content of all nitrogen oxides is measured and the calculated difference between NO2 and NOX measurement indicates the concentrations of both components.

Measuring principle of CLDmono

CLD mono principle, Prinzip CLD, Chemilumineszezspektroskopie

With the CLDmono​, the sample gas can be alternately passed through and past the NOX converter. This means that NO and NOX can be measured alternately with one reaction chamber (measuring chamber). With the CLDdual​, a second measuring chamber enables simultaneous measurement of the two gases.

Measuring principle of CLDdual

CLD dual principle, Prinzip CLD, Chemilumineszezspektroskopie

Direct measuring method

Extremely stable measurement

High dynamic range

Extremely low maintenance

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