Nitric Oxide-Nitrogen Dioxide Detector

Nitric Oxide Pass 550 50 mL of sample gas, released from the vapor phase of the contents of the sample gas cylinder, through a nitric oxide-nitrogen dioxide detector tube at the rate specified for the tube. The indicator change corresponds to not more than 1 ppm, by volume. 

The oldest chemiluminescent detector was the thermal energy analyzer (TEA), which was specific for N-nitroso compounds. N-nitroso compounds such as nitrosamines are catalytically pyrolyzed and produce nitric oxide which reacts with ozone to produce nitrogen dioxide in the excited ] state, which decays to the ground state with the emission of a photon. A photomultiplier in the reaction chamber measures the emission. Nitrosodi-methylamines have been detected to about 30-40 pg [108]. 

More recently, chemiluminescence detectors based on redox reactions have made possible the detection of many classes of compounds not detected by flame ionization. In the redox chemiluminescence detector (RCD), the effluent from the column is mixed with nitrogen dioxide and passed across a catalyst containing elemental gold at 200-400°C. Responsive compounds reduce the nitrogen dioxide to nitric oxide. The nitric oxide is reacted with ozone to give the chemiluminescent emission. The RCD yields a response from compounds capable of undergoing dehydrogenation or oxidation and produces sensitive emissions from alcohols, aldehydes, ketones, acids, amines, olifins, aromatic compounds, sulfides, and thiols. 

During the course of the irradiations, the concentrations of the following variables were monitored oxidants (Mast coulometric ozone meter) (4), condensation nuclei with radii greater than lO " cm (G.E. Type CN small particle detector) (5), ozone (Regener chemiluminescent ozone meter (6), nitrogen dioxide and nitric oxide (Saltzman method) (7), and a-pinene (Perkin Elmer model 800 gas chromatograph). 

The use of NCD, especially in pharmaceutical applications, have focused on exploiting the chemiluminescence properties of nitrogen dioxide (NO2) formed from the high-temperature combustion of nitrogenous compounds [6-8]. This type of detector, originally developed for GC by Parks and Marietta [9], forms nitric oxide followed by ozone-induced chemiluminescence. The reaction is characterized as follows ... 

The redox chemiluminescence detector (RCD) is also based on the nitric oxide-ozone reaction. However, unlike the two detectors previously described, the analytes do not contain any oxidizable nitrogen. In this case a nitrogen-containing reagent such as nitrogen dioxide or nitric acid is reduced to nitric oxide by the analyte at a heated gold surface (reaction [IV]) ... 

---