Ozone sampling

Schueler B, Morton J, Mauersberger K (1990) Measurement of isotopic abundances in collected stratospheric ozone samples. Geophys Res Lett 17 1295-1298... 

Location of the Modified Residues. In order to determine the location and number of amino acid residues reacted with ozone, the ozonized samples were allowed to undergo cyanogen bromide cleavage and trypsin digestions. 

TABLE 5.3 Trace Metal Determination after Ozone Sample Treatment Elements Analytical ... 

Ozonization of the polypropylene powder creates the peroxidic species in the polymer, as well. The activation energy [41] of the thermal decomposition of these peroxides is 100 kJ/mol. In the decomposition of peroxides more than one type of radicals was trapped. Moreover, the three exotherms (peak at 40,90, and 130 °C) were observed on DSC thermograms of ozonized sample which also indicates the presence of several types of peroxides. Besides the peroxidic bonds in polymer, selective thermal decomposition may occur also with such bonds in the polymer as, e.g., with end groups containing the initiator moieties [42], This, however, takes place at higher temperatures than it corresponds to usual temperatures at which the thermo-oxidation starts. 

Different purified dye concentrations (14.4, 7.2, and 3.6 x lO 2 mmol/L) and saturated ozone concentrations in excess (by adjusting air-flow rate) were applied to investigate the reaction kinetics of dye ozonation. Samples were collected from the contact tower at times of 0, 5, 15, 30, 60, 120 and 180 minutes, then the residual dyes were analyzed by HPLC for quantification. Three initial pH values of 4, 7 and 10 adjusted by sulphuric acid or sodium hydroxide were used to examine the consequence of the initial pH values on the overall reaction rates. 

For an objective consideration on the enthalpy changes it is neeessary to normalize A/f values with respeet to the amount of consumed ozone (G). It is distributed on the whole mass of the ozonated sample. The whole mass is a sum of the mass of nonozonated rubber and mass of the incorporated in diene macromolecules oxygen atoms, grouped as a moles ozone. Determination of the amounts of the incorporated ozone in rubber samples is performed in [43], The corresponding values of the coefficient of incorporation of ozone (c. ), defined as a ratio of the amounts of incorporated (G ) and consumed (G) ozone is Presented in Table 10.6. Using A//j values and ratio of the functional group, deduced from the NMR spectra, the enthalpy of the ozonide thermal decomposition (AH has been evaluated. The data of Table 10.6 clearly show tendency of increasing of AH values with the number of alkyl substituents of the ozonides. 

See also Amperometry. Atomic Emission Spectrometry Flame Photometry. Chemiiuminescence Overview Liquid-Phase. Flow Injection Analysis Principles. Fluorescence Quantitative Analysis. Ion Exchange Ion Chromatography Instrumentation. Liquid Chromatography Overview. Ozone. Sampling Theory. Sulfur. Textiles Natural Synthetic. 

Direct measurement of UV absorbance is applicable to aqueous ozone. Unfortunately, the molar absorptivity at 260 nm has not yet been exactly established 3290mol 1 cm is considered to be reasonable out of the reported values ranging from 2900 to 3600 mol 1 cm For real aqueous ozone samples, special care should be taken to avoid interferences from coexisting substances. Background absorbance can be determined after destruction of the residual ozone with an excess of nitrite or butenol. 

The melting point appears to be a very sensitive parameter in investigating the behavior of the ozonized samples. From Figs. 31 and 32, it is observed that an antibat dependence between the curves illustrating the dependence of the oxidation level on composition and T.j. of the crystallites in blends with various PE content. The periods of acceleration, retardation and of maximum occurrence correspond to decrease, increase and minimum appearance depending on T. of the PE crystallites in the mixture composition. 

First of all we have to note the decrease in the values of k for PE and PP with the decrease of their content in the mixture both for the nonozon-ized and in the ozonized samples. However, in the case of the nonozonized samples the profile of k is characterized by a range whereby it is constant. 

In the case of PE the values of k for the ozonized samples are found to be higher than those of the nonozonized ones. An exception are the samples containing 10 and 20% PE for which k falls down abruptly. The increase, probably could be explained by the fact that ozone does not penetrate into the PE crystallites but rather reacts with PE in the transition zone on their surface. This reaction leads to break of the macromolecules in the transition zone and thus the crystallinity is enhanced on account of the section that provided by the cut-off molecules in the transition zone. The authors of Ref 118 have also observed a similar increase of k for PE during its ozonation. These changes of K are also demonstrated by the curves in Fig. 33. 

It has been found that the values of k in the PP crystallites of ozonized samples are always higher as compared to that in the nonozonized ones (Fig. 33). This observation could be related to the fact that ozone penetrates into the crystallites and reacts further with tert C-H bonds. Thus they are gradually crushed and transformed in an amorphous state. This phenomenon is characterized by a decrease of T and k in the ozonized samples whereby the initial content of PP was lower than 30% and the crystal structure is completely destroyed. 

For PE, Ah in the ozonized samples is higher than that of the nonozonized ones in the whole range of the mixtures composition with an exception of the pure PE and the mixture with 1 9 content. The comparison of the relationship between Ah and k allow us to assume that the increase in polydispersity of PE cr) tallites can be explained by physical reasons stipulated by the mixture composition. Thus, in mixtures with high PE content ranging from 30 to 100% is observed a simultaneous increase of Ah and... 

It has been found that the polydispersity of PP crystallites monotonously decrease with the decrease of PP content in the mixtures (Fig. 34). In each case the polydispersity and k in the ozonized samples are always lower than those in the nonozonized ones in the whole range of mixtures composition. Apparently, the decrease in the PP polydispersity is associated with its initial reaction with the smallest crystallites. 

The analysis of the IR spectra of the ozonized samples (Table 13) shows that the content of t-CH -groups practically does not change during ozonolysis as the intensity of the bands at 700 and 2930 em do not change essentially. 

This method, described by T. Sarraf, involves a free radical scavenger diphenyl picryl hydrazil, DPPH. DPPH, stable at room temperature, is added in excess to the ozonized sample and reacted at 110°C. The cleavage of peroxides and hydroperoxides to RO and HO generates free radicals which are captured by DPPH. After precipitation of polyethylene, the excess of DPPH in the filtrate is back-titrated by colorimetry at 520 nm, and the amount of initial peroxides and hydroperoxides can be obtained from the result. 

The results show that ozonization decreases the molecular weight of polyethylene molecules. The molecular mass of the ozonized product is approximately twice lower than that of initial product. Moreover, the polydispersity index rapidly increases, which indicates that chains, broken during the ozonization, have different sizes. When we examine the results obtained with the ozonized sample deactivated on bitumen, we notice that the molecular mass increases and is in the range of the standard polyethylene molecular mass. This increase can only be due to two phenomena ... 

As a result of their chemically saturated structure, the fluoroelastomers display excellent weathering resistance to sunlight and especially to ozone. Samples exposed to various tropical conditions in Panama for 10 years showed little or no change in properties. Similar results were experienced after 13 years of exposure in direct Florida sunlight. 

For an objective consideration on the enthalpy changes it is necessary to normalize DH values with respect to the amoimt of consumed ozone (G). It is distributed on the whole mass of the ozonated sample. The whole mass is a siun of the mass of nonozonated rubber and mass of the incorporated in diene macromolecules oxygen atoms, grouped as a moles ozone. Determination of the amoimts of the incorporated ozone in rubber... 

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