Oxidation measurement

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

Figure 2.39. (a) Effect of pcc/Pc>2 on the rate °f CO oxidation (measured as PC02) on Pt(l 11) covered with various Li coverages 0Lj 12 (b) Effect of Li coverage on the rate of CO oxidation at various fixed Pcc/po2 values.112 Reprinted with permission from Elsevier Science. 

In the Dickinson et al. studies, the results of microelectrode measurements indicated that eimohlement was not caused by elevated levels of dissolved oxidants. Measurements at various heights above the substratum and at numerous sites over the coupon surface showed HjOj concentrations < 2 pM and no significant variation in for the stainless steel microelectrode at any site. DO profiles in the same regions showed saturation levels at all sites. Representative profiles are shown in Fig. 11. 

In table 1, we show the influence of the degree of fluorination of the chromium oxide (measured by F/Cr atomic ratio.) on the transformation of CF3CH2CI. We remarked that the longer the fluorination of the catalyst lasts, the greater the degree of fluorination Moreover this fluorination decreases slightly the specific surface of the catalyst.. Fluorination and dehydrofluorination activities per unit of surface show the same evolution whatever the degree of fluorination... 

T. Malinski, F. Bailey, Z.G. Zhang, and M. Chopp, Nitric-oxide measured by a porphyrinic microsensor in rat-brain after transient middle cerebral-artery occlusion. J. Cereb. Blood Flow Metab. 13, 355-358 (1993). 

K. Ichimori, H. Ishida, M. Fukahori, H. Nakazawa, and E. Murakami, Practical nitric-oxide measurement employing a nitric oxide-selective electrode. Rev. Sci. Instrum. 65, 2714-2718 (1994). 

Y. Kitamura, T. Uzawa, K. Oka, Y. Komai., H. Ogawa, N. Takizawa, H. Kobayashi, and K. Tanishita, Microcoaxial electrode for in vivo nitric oxide measurement. Anal. Chem. 72, 2957-2962 (2000). 

It has also been shown that LDL oxidation is increased in diabetes. In this connection, Mowri et al. [179] studied the effect of glucose on metal ion-dependent and -independent LDL oxidation. They found that pathophysiological glucose concentrations enhanced copper- and iron-induced LDL oxidation measured via the formation of conjugated dienes. In contrast, glucose had no effect on metal-independent free radical LDL oxidation. Correspondingly,... 

Oxygen Diffusion Coefficient (D ), Oxygen Surface Exchange Coefficient (Ar), and Oxygen Ionic Conductivity (tr,) of LaMn03-Based Oxides Measured by SIMS Technique... 

It was found that the concentration of total oxidants measured in the off-gas from the hypo unit varied with process conditions. Precise analysis of the off-gas showed that under certain conditions chlorine dioxide is formed in the reaction step where the hypochlorite concentration is approximately 160-180 g l-1. In the sections below formation of chlorine dioxide in the hypochlorite unit is discussed with regard to process conditions and peak load of the feed stream. In essence, the emission of chlorine dioxide can be reduced to nearly zero by using a scrubber in which the chlorine dioxide reacts with hydrogen peroxide. 

In summary, chemiluminescence is a sensitive, non-invasive technique that can measure reactive oxidant production by small numbers of neutrophils indeed, neutrophil-derived chemiluminescence can be detected in as little as 5 fA of unfractionated human blood. The assay is suitable for automation using either multichannel luminometers or luminescence microtitre plate readers. Many researchers, however, have questioned the usefulness of this technique because of the uncertainty of the nature of the oxidant(s) that are detected. Nevertheless, in view of the recent developments made towards the identification of the oxidants measured and the assay s ability to detect intracellular oxidant production, it is has an important place in the phagocyte research laboratory. 

California Air Resources Board. Final Report of the ad hoc Oxidant Measurement Committee. Report No. 75-4-4. Sacramento California Air Resources Board, Feb. 20. 1975. 47 pp. 

Bilger has documented ozone and other oxidant measurements in Australia and compared them with those in other cities. Table 4-6 shows the portion of hours during which threshold concentrations were exceeded in Sydney in 1971, 1972, and 1973. Low concentrations were recorded before 1970, probably because of the proximity to nitric oxide emission sources in the central portion of the city. It is also noteworthy that, despite the calm conditions and strong inversion in the winter months (in the Southern Hemisphere), high-oxidant days were relatively infrequent. Figure 4-8 outlines this seasonal variation in oxidant concentration. In Melbourne, Australia, however, a high-ozone episode was observed during... 

Nonurban oxidant measurements in Ohio were reported by Neligan and Angus. Concentrations of 0.18 and 0.12 ppm were reported for rural sites in Wilmington and McConnelsville, respectively. At the same time, urban sites had similar concentrations. However, the nonurban sites violated the ambient air quality standard more frequently than the urban sites. Trajectory analysis showed that ozone concentrations of 0.04-0.06 ppm were found in air masses that had not passed over anthropogenic hydrocarbon sources. These may have been examples of naturally occurring oxidant. Airborne hydrocarbon bag samples were obtained over 6-min... 

A dramatic departure of ozone measurements from total oxidant measurements has b Mi reported for the Houston, Texas, area. Side-by-side measurements suggested that either method was a poor predictor of the other. Consideration was given to known interferences due to oxides of nitrogen, sulfur dioxide, or hydrogen sulfide, and the deviations still could not be accounted for. In the worst case, the ozone measurements exceeded the national ambient air quality standard for 3 h, and the potassium iodide instrument read less than 15 ppb for the 24-h period. Sulfur dioxide was measured at 0.01-0.04 ppm throughout the day. Even for a 1 1 molar influence of sulfur dioxide, this could not explain the low oxidant values. Regression analysis was carried out to support the conclusion that the ozone concentration is often much higher than the nonozone oxidant concentration. 

Frydman, M.. A. Levy, and S. E. Miller. Oxidant measurements in the vicinity of energized 765 kV lines, pp. 1141-1147. In IEEE (Institute of Electrical and Electronics Engineers) Transactions on Power Apparatus and Systems, May-June, 1973. 

Qukkert, N., H. Oja, and J. L. Monkman. Summary of Oxidant Measurements in Canada. Ottawa, Canada Environmental Protection Service, Air Pollution Control Directorate, (1973J. 78 pp. 

Whether ozone or oxidant measurements can be correlated with other variables depends heavily on the choice of sampling site and the manner of sample transfer. The importance of these criteria is discussed in Chapter 5, and the desirable specifications are described in this chapter. 

Hodgeson, J. A. Review of analytical methods for atmospheric oxidants measurements. Int. J. Environ. Anal. Chem. 2 113-132, 1972. 

Field surv have confirmed oxidant injury to ponderosa pine and associated species at numerous locations in the Sierra Nevada foothills east and southeast of Fresno. Oxidant measurements at ground stations and by instrumented aircraft show late-aftemoon peaks of transported oxidant on the western slopes of the Sierras. Limited measurements by instrumented aircraft suggest the development of a layer of oxidant approaching the forested mountain slopes between 610 and 1,829 m during the late afternoon. A very weak inversion or isothermal layer may serve as a reservoir of oxidant, which is advected to the mountain slope in the southern coastal air basin, as suggested by Edinger. Considerable concern has been registered about air quality in the Lake Tahoe basin, where local development may cause adverse oxidant concentrations. ... 

Due to the tendency of hydrocarbons in the soil to undergo subsurface oxidation, measuring COj levels in the soil gas could be used as a cost-effective field screening tool. In one soil-gas survey, COj levels in soil gas correlated well with petroleum hydrocarbons in the soil (Diem et al. 1988). 

Figure 2.9 Mn(L) edge and 0(K) edge in the EELS of manganese oxides measured in an electron microscope. (Rao et ai, 1984.)...

Rate of biological inactivation of nitric oxide. The apparent first-order rate constants were calculated as the natural logarithm of two divided by the half-life of nitric oxide measured in perfusion cascades. The half-lives were 30 sec with room air and 6-8 sec with 95% oxygen (Furchgott and Vanhoutte, 1989). Under anaerobic conditions, nitric oxide is indefinitely stable. The slope of the line give a second-order rate constant for the inactivation of nitric oxide by oxygen as approximately 100 M" sec". ... 

Destruction of nitric oxide by superoxide in the buffers is more likely to account for the short half-life of nitric oxide in vitro. Superoxide dismutase (15-100 U/ml) substantially increased the apparent half-life of EDRF, strongly suggesting that superoxide contributes to the short biological half-life of nitric oxide. In the perfusion cascade bioassay system, the buffers are bubbled with 95% oxygen, contain 11 mM glucose as well as trace iron plus copper contamination and are incubated under the weak ultraviolet (UV) radiation of fluorescent lights. These are prime conditions for the autoxidation of glucose to form small amounts of superoxide in sufficient amounts to account for the short half-life of nitric oxide in nanomolar concentrations. The rate of reaction between superoxide and nitric oxide is 6.7 X 10 M sec L The shortest half-life of nitric oxide measured is approximately 6 sec. To achieve a half-life of 6 sec, the steady state concentration of superoxide would only need to be 17 pM, calculated as ln(2)/ (6 sec X 6.7 X 10 M" sec )-... 

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