Chemiluminescence nitric oxide detection

Chemiluminescence. Chemiluminescence (262—265) is the emission of light duting an exothermic chemical reaction, generaUy as fluorescence. It often occurs ia oxidation processes, and enzyme-mediated bioluminescence has important analytical appHcations (241,262). Chemiluminescence analysis is highly specific and can reach ppb detection limits with relatively simple iastmmentation. Nitric oxide has been so analyzed from reaction with ozone (266—268), and ozone can be detected by the emission at 585 nm from reaction with ethylene. 

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. ... 

NO Nitric oxide is most commonly measured using the chemiluminescence from its reaction with 03 described earlier. One such instrument designed for high-sensitivity (1- to 2-ppt detection limit in 10 s) is described by Ridley and Grahek (1990). 

Nitric oxide release from blood vessels was first detected by chemiluminescence (Palmer et ai, 1987). In the original adaptations of the nitric oxide detector, perfusates from isolated vessels were directly mixed in a reflux chamber containing acetic acid and iodine. The iodine in the reflux chamber served to reduce any nitrites or nitroso-containing groups to nitric oxide, which was stripped from the chamber by a continuous stream of nitrogen or helium that flowed to the chemiluminescent detector. Replacement of the acetic acid with the less volatile trichloroacetic acid reduces problems with contamination of the nitric oxide detector (Dr. D. Harrison, Emory University, Atlanta, Georgia, personal communication, 1991). While extremely sensitive, the use of the acid reflux chamber also reduces the specificity of the assay, raising questions as to whether nitric oxide or a nitrosothiol is EDRF (Myers et ai, 1990). 

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. 

A recent approach is the use of combustion followed by chemiluminescent detection of nitric oxide produced in the combustion (Drushell, 1977). The senior author s experience is that response of this detector apparently is dependent on the composition of the sample, and that therefore the instrument must be standardized with materials very similar to the unknown (Schuchardt, 1980). 

Drushell, H. V. (1977). Determination of nitrogen in petroleum fractions by combustion with chemiluminescent detection of nitric oxide. Anal. Chem. 49, 932-936. 

After pyrolysis and reduction, the gas mixture containing nitrogen passes through a trap to remove water and the combustion gases (Figure 18.4). The general detection procedure, based on the thermal conductivity of the gas, is replaced by specialized detectors based on the chemiluminescence of nitric oxide (NO) when combined with ozone (O3) (cf. Section 11.8). 

Molecular imprinted polymer recognition and on line electrogenerated chemiluminescence detection. Most CL results from a direct oxidation reaction or an oxidation reaction with energy transfer. Commonly used oxidants include hydroperoxide, oxygen, potassium permanganate, ferricyanide, tetravalent cerium ion, lead dioxide and oxygen free radical such as superoxide anion ( 02 ), hydroxy radical ( OH) and nitric oxide (NO). 

Chan, W.G. and W.P Hempfling Chemiluminescence detection of nitric oxide for the analysis of total A-nitroso compounds in tobacco 53rd Tobacco Science Research Conference, Program Booklet and Abstracts, Vol. 53, Paper No. 86, 1999, pp. 67-68. 

Nitrogen containing analytes (R-N) are oxidized in a furnace at high temperatures to nitric oxide ( NO). Chemiluminescence as shown in the second equation is detected by a photomultiplier tube (PMT). The photons detected are proportional to the amount of nitrogen in the analyte(s). 

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