Sequential or simultaneous measurement of NO and NOX !
CLD-chemiluminescence detector
The described Ç-hemiluminescence effect is used to measure the concentration of NO and NO X. The molecule can transfer the electronic ground state to the excited electronic state by energy absorption. The absorbed energy can be emitted again during the transition to a lower energy state. This occurs on the one hand in the form of heat (non-radiative deactivation) and on the other hand in the form of light (luminescence). Especially during combustion processes nitrogen oxides are produced, which is why this analytical method is used in exhaust gas measurement technology for power plants, in the automotive industry and in environmental technology.
Chemiluminescence principle
Chemiluminescence is the light emitted after excitation of molecules during a chemical reaction. It is used in the analysis of nitrogen gas.
Nitrogen monoxide reacts with ozone to form nitrogen dioxide.
The subsequently emitted light (proportional to the NO concentration) is measured and amplified by a photomultiplier.
In order to analyze advanced nitrogen oxides, a catalyst (NO X converter) must be used to reduce them to nitric oxide.
NO + O 3 →NO 2 * + O 2
NO 2 * →NO 2 +hν (luminescence)
If all nitrogen oxides should be measured in a single sample stream, the amount of nitric oxide must first be measured.
This measurement is performed without a catalyst. Subsequently, the gas stream is made to pass through the catalyst, so that all nitrogen oxides (e.g., NO 2) are reduced to NO.
The content of all NOx is measured and the difference between the calculated NO 2 and NO X measurements indicates the concentration of the two components.