Description of a Chemiluminescent Detector System Specifically Designed for Monitoring Airborne Hydrazine Propellants, Hydrazine, Monomethylhydrazine and Unsymmetrical Dimethylhydrazine,
THERMO ELECTRON CORP WALTHAM MASS
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A new prototype ambient air monitoring system designed to specifically detect airborne levels of all three of the commonly used hydrazine propellants, hydrazine HZ, monomethydrazine MMH and unsymmetrical dimethylhydrazine UDMH is presently being developed and evaluated. The basic system consists of a modified nitrogen oxide NO chemiluminescent detector equipped with a dual-channel air sampling system in which sampled air is split equally between a reference channel and a hydrazine channel. The hydrazine channel differs from the reference channel in that 1 to 5 of the sampled air is replaced by nitrogen gas containing 10 acetaldehyde approximately 3 to 5000 parts per million ppm acetaldehyde in the air stream. The added acetaldehyde rapidly converts airborne hydrazines to their respective hydrozones or azine derivatives. The air samples in both channels are heated to 750 C in a pyrolyzer containing a nickel oxide catalyst which rapidly converts most airborne nitrogen compounds, including oxides of nitrogen, to molar equivalent amounts of NO. The NO produced by the oxidation is then combined with ozone O3 in an evacuated reaction chamber resulting in an infrared emitting chemiluminescent reaction which is proportional to the NO concentration in the gas stream. The chemiluminescent reaction chamber is equipped with an infrared filter and a highly sensitive photomultiplier tube which is similar in design to that routinely used by commercial NOx detectors to monitor how part-per-billion ppb levels of atmospheric NO and NOx.