Optical microscopy representative analysis

Raman microspectroscopy is readily performed on multiple locations inside each well. As in other instances, the results might not be representative of the whole sample because of the small sample volume probed. Polarization effects can be pronounced, but may be mitigated by averaging the results from additional locations. An alternative is rotating the sample, but this usually is not practical for multiwell plates. Both options increase analysis time. Such problems appear to be minimized when handling bulk powders [222,223,230], Several vendors sell systems preconfigured for automated analysis of microtiter plates and are typically integrated with optical microscopy. 

Another point to consider is that the penetration depth for fluorescent X-rays depends on their energy. Thus, the map for Ca will represent material closer to the surface than that of Zn (Fig. 20). This effect can distort the results of correlation analysis because the maps for different elements will represent different volumes. Since the incident beam is usually not normal to the surface, features deep inside the sample will appear out of registry with those nearer the surface. The net effect is as if the sample is viewed from the direction from which the beam comes, rather than straight on, as is usually the case for optical microscopy. 

The first step in the analysis of suspected illicit materials is to categorize the sample [96,98], A representative sample is first subjected to radiological analyses to determine the activity and type of radiation produced (a, P, or Y radiation). The sample is then visually inspected and subjected to optical microscopy and radiography to gain knowledge of the material s crystal structure and microstructure, respectively. The material is then characterized by MS to determine the exact isotopic composition of the compound. The isotopic composition of the material can describe the origins (natural or human-made) of the sample and suggest the type of process used to make the material. 

Optical microscopy is also a technique that can be useful for the characterization of nanocomposites. According to Xie ct al. [27] transmission electron microscopy has been widely used to estimate clay dispersion and orientation in polymer matrices. Although it can provide direct information on clay layers in the real space, the analysis are focused on a very small volume of the sample and may not be representative. However, optical microscopy can be a complementary technique to substitute for analyze the overall dispersion/distribution of day partides at a macroscopic level. It can show, for example, the presence of agglomerate partides that can be related to the degree of exfoliation of clay layers in the matrix. 

Some light scattering measurements require knowledge of a particle s optical properties. The light scattering analysis uses these optical properties in a model for the calculation of particle size, and for accurate results you need to choose a model that best represents these optical properties. Picking an improper model will yield inaccurate results. Microscopy only requires a small amount of material and can be used to quickly measure these optical properties. 

One objective of a kinetic analysis is to identify which, if any, of the rate equations (in an appropriate form) from Table 3.3. provides the most acceptable description of the experimental a, tor a, T data. In deciding what constitutes an "acceptable description", there are at least two main aspects to be considered (i) the purely mathematical "fit" of the experimental data to the relationship between a and t, (da/dt) and t or (da/d/) and a, required by the models listed in Table 3.3., together with the range of a across which this expression satisfactorily represents the data (whether the fit varies with temperature is also important) and (ii) the evidence in support of a kinetic model obtained by complementary techniques such as optical and electron microscopy, spectroscopy etc. (see Chapter 6). 

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