Qualitative Identification of Phases

FIGURE 4.2 XRD pattern of the opal sample 81C with an AlP04-5 microporous molecular sieve synthesized on the surface. 

Ion-exchange reactions were used for the accumulation of europium(III) [158] and iron(III) [159] ions on the surface of GCE coated with Nation , and chromium(VI) ions on the surface of GCE covered by a pyridine-functionalized sol-gel film [160], which were combined with the stripping SWV. Eurthermore, a cathodic stripping SWV was used for the determination of sulfide [161,162], thiols [163-166], selenium(IV) [167-170], halides [171-173] and arsenic [174] accumulated on the surface of mercury electrode. 

The SWV of microparticles of the lipid-lowering drug simvastatin is shown in Fig. 3.8 [188]. The electrode reaction is totally irreversible, as indicated by the backward component of the response. The net peak potential is a linear function of the logarithm of SW frequency, as can be seen in Fig. 3.9. From the slope of this relationship (79 mV/d.u.) the product an = 0.75 was calculated [188]. These examples show that SWV can be used for the characterization of electrode reactions of microparticles immobilized on solid electrodes. 

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The simplest solid—solid reactions are those involving two solid reactants and a single barrier product phase. The principles used in interpreting the results of kinetic studies on such systems, and which have been described above, can be modified for application to more complex systems. Many of these complex systems have been resolved into a series of interconnected binary reactions and some of the more fully characterized examples have already been mentioned. While certain of these rate processes are of considerable technological importance, e.g. to the cement industry [1], the difficulties of investigation are such that few quantitative kinetic studies have been attempted. Attention has more frequently been restricted to the qualitative identifications of intermediate and product phases, or, at best, empirical rate measurements for technological purposes. 

Characterization of Samples. Powder diffraction patterns of the samples were obtained with a Philips diffractometer using monochromated high-intensity CuKai radiation (X = 1.5405A). For qualitative identification of the phases present, the patterns were taken from 12° < 20 <72° with a scan rate of 1° 20/min and a chart speed of 30 in/hr. The scan rate used to obtain x-ray patterns for precision cell constant determination was 0.25° 20/min with a chart speed of 30 in/hr. Cell parameters were determined by a least-squares refinement of the reflections. 

The resolutions and signal to noise ratios of natural abundance 15N NMR spectra of nylons are sufficient to detect individual absorptions arising from morphologically different phases in nylons. In addition, the NMR data, which give immediate qualitative identification of the type of crystallinity, do not depend as much on size and perfection of the crystalline regions as X-ray analysis [56, 57], However, the broad unresolved peaks and shoulders on sharp... 

The qualitative identification of materials and components in mixtures by solid-solid phase transition temperatures and melting points. 

A 1.1 The logarithmic Kovats Retention Index is a gas chromatographic parameter characteristic of a solute s relative retention on a specified liquid phase at a specified (isothermal) temperature. It is a very useful tool in the qualitative identification of chromatographic peaks. 

X-Ray and electron diffraction measurements have been most usually used to characterize the phases present in any reactant mixture, and provide a means of identification of solid reactants, intermediates and products. In addition to such qualitative analyses, the method can also be used quantitatively, with suitable systems, to determine the amounts of particular solids present [111], changes in lattice parameters during reaction, topotactical relationships between reactants and products, the presence of finely divided or strained material, crystallographic transformations, etc. 

Qualitative (identification) applications depend upon the comparison of the retention characteristics of the unknown with those of reference materials. In the case of gas chromatography, this characteristic is known as the retention index and, although collections of data on popular stationary phases exist, it is unlikely that any compound has a unique retention index and unequivocal identification can be effected. In liquid chromatography, the situation is more complex because there is a much larger number of combinations of stationary and mobile phases in use, and large collections of retention characteristics on any single system do not exist. In addition, HPLC is a less efficient separation... 

After extraction, each phase may be studied independently in order to obtain a useful qualitative evaluation of the components in the original sample. The selectivity and specificity of fluorescence analysis can be especially beneficial in identification of PAHs. For example, some components could be identified by examining the fluorescence spectra of the organic and aqueous phases. Characteristic peak shapes may reveal identities of the components. For more complicated systems in which the spectra overlap, lifetime measurements may be used to identify components (27). 

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