Nitric oxide measurement techniques

Electrochemical cells are sometimes used to measure nitric oxide and nitrogen dioxide. These, together with nitrous tixide (N2O), are measured using the ITIR techniques. 

Here a chemical reaction produces a molecule with electrons in an excited state. Upon decay to the ground state the liberated radiation is detected. One such example is the reaction between ozone and nitric oxide to form nitrogen dioxide emitting radiation in the near infra-red in the 0.5-3/t region. The technique flnds use for measuring nitric oxide in ambient air or stack emissions. 

Brovkovych et al. [38] applied the electrochemical porphyrinic sensor technique for the direct measurement of NO concentrations in the single endothelial cell. It was found that NO concentration was the highest at the cell membrane (about 1 pmoll-1) and decreased exponentially with distance from the cell, becoming undetectable at the distance of 50 pm. Now we will consider the principal reactions of nitric oxide relevant to real biological systems. 

In the measurement of nitrqgen dioxide with this technique, it is thermochemically converted to nitric oxide by reaction with molybdenum at about 200 C. The extent of possible interferences at various monitoring sites from nitrogen compounds other than amhionia, which does not interfere unless the temperature is considerably higher than 2(X) C, remains to be assessed. The instrumentation of this procedure is inherently more reliable than the original colorimetric analyzers. Unfortunately, the mutual equivalence in monitoring situations of data obtained by these two techniques has not yet been evaluated. This is particularly important for the data from California, where the colorimetric method has been used for more than 20 yr. 

In flue gases MISiC sensors can be used to either monitor the gas components, such as CO, nitric oxide (NO), and oxygen, or identify different modes of combustion in the boilers of small power plants. In this way, it is possible to optimize the combustion in boilers of about 0.5-5 MW in which optical techniques such as Fourier transform infrared (FTIR) are too expensive and complex. The authors have performed measurements in a 100-MW boiler, which has been used to heat houses and industries and generate electricity in Nykoping, Sweden, and in which there was a natural randomization of the flue gases [59]. Data was collected over several... 

The rate of decay of nitrosomethane (formed in the photolysis of azomethane-nitric oxide mixtures at 25° C) to form the stable dimer, reaction (2), was measured by infrared techniques and the homogeneous second order rate coefficient = 87 l.mole. sec was derived. The cis and trans iomers of nitrosomethane have been characterized and the experimental conditions which favour the formation of each of the dimers and the rearrangement to formaldoxime have been described ... 

Additionally, in a microreactor the intrinsic kinetics and deactivation behavior of SCR catalysts is studied with flows up to 1.5m h . In both test facilities it is possible to vary all process parameters temperature, the ammonia to nitric oxide feed ratio, the nitric oxide and sulfur dioxide concentrations, the space velocity, and the catalyst geometry. These techniques provide information for somewhat small areas and therefore should always be performed to complement bench- or laboratory-scale activity and selectivity measurements. 

The complexity and plasticity of BBB properties called for experimental dissection of the disrnption process in both in vitro and in vivo conditions. Multiple cell and organ cnltnres, animal models, and measurement techniques have been developed, each of which addresses some of the issues involved. The development of research into BBB characteristics was initially approached in avian embryos, where transplanted endothelial quail cells invaded a developing chick chimera. A simpler cell culture model of the BBB was developed by Rubin and co-workers. More recently, an immortalized cell line created from vascular endothelial cells was used to develop another model of the BBB in co-cultures with glioma cells and was used to demonstrate nitric oxide-induced perturbations of these cells. hi another cell culture model, hypoxia was shown to increase the susceptibility to oxidative stress and intercellular permeability. ... 

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