Ozone chemiluminescence, nitrogen oxide

An instrument for measuring nitrogen oxides based on chemiluminescence is shown in Fig. 13.49. The ozone required for the reaction is produced in the ozone generator, which is part of rhe device. One of the reaction chamber walls is an optical filter through which a red-sensitive photomultiplier tube measures the chemiluminescence radiation intensity and converts it into a current signal. 

Chemiluminescent techniques have been used to determine nanomolar quantities of nitrate and nitrite in seawater [124,125]. This method depends on the selective reduction of these species to nitric oxide, which is then determined by its chemiluminescent reaction with ozone, using a commercial nitrogen oxides analyser. The necessary equipment is compact and sufficiently sturdy to allow shipboard use. A precision of 2nmol/l is claimed, and an analytical range of 2nmol/l with analysis rates of 10-12 samples hourly. 

The technol( for the routine measurement of the nitrogen oxides (nitrogen dioxide and nitric oxide) is fairly well advanced. The epa is on the verge of officially proposing that chemiluminescence produced by the reaction of nitric oxide with ozone be the reference method for nitrogen dioxide.This method is even more suitable for nitric oxide. Because no national air quality standard has been promulgated for nitric oxide, no reference method will be specified. However, its measurement in the atmosphere is crucial for establishing the relation of its emission to the formation of atmospheric ozone and other photochemical oxidants. 

In the chemiluminescent detection of nitrogen oxides, a constant source of ozone reacts with a metered air sample containing nitric oxide. Fontijn et al. suggested that this method could also be used for ozone detection by using a constant nitric oxide source for reaction with ozone in the air sample. The ozone-nitric oxide reaction is carried out at reduced pressure, to avoid quenching the chemiluminescent reaction. Detection of the emission in the spectral r on involved (600-3,000 nm) requires using a near-infrared-sensitive photomultiplier tube. The noise of such a photomultiplier tube is reduced by cooling it to about - 20 C. ... 

The calibration of a chemiluminescent analyzer using these standards is verified when both the nitrogen dioxide and nitric oxide channels respond similarly to charges from the (ylinder of diluted nitric oxide. Agreement with the response of the nitric oxide channel should also be obtained when the standard nitric oxide mixture is titrated with a previously established source of ozone. Chemiluminescent instruments have simplified monitoring of nitrogen oxides, but accurate calibration requires well-trained personnel. 

This reaction can be utilized for determining the nitrogen oxides content in gas mixtures. The NO concentration can be measured separately using the chemiluminescence of the NO + ozone reaction. 

Difficulties are encountered in determining NO2 using the ozone-chemiluminescence technique due to the non-specific conversion of several nitrogen oxides/oxyacids on the Mo catalyst. Use of FeS04 f°r N02-to-N0 conversion has been described, but humidity-dependent sorption/desorption effects have been reported, e.g., PAN (11). Alternatively, a commercial NO2 analyzer based on surface chemiluminescence of NO2 in the presence of a luminol solution, has been introduced which exhibits the requisite sensitively and selectivity. 

Among other methods is that based on the chemiluminescent reaction of nitrogen oxide with ozone ... 

Reports on sensors for nitrogen oxides (NOj ) are scarce, although there are various observations as to the quenching of the fluorescence of polycyclic aromatic hydrocarbons by NO. This may be utilized for sensing purposes. The chemiluminescence produced in the reaction between NO and ozone is another attractive possibility that might be exploited for this purpose. 

Table 1 Some applications of nitrogen oxide-ozone chemiluminescence...

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