Analytical methods optical microscopes

The computer age has brought about considerable innovation in the operation of laboratory instrumentation. One consequence of this is the wider acceptance and utilization of the optical microscope as a quantitative analytical instrument. A brief literature survey illustrates the diversity of disciplines and optical methods associated with the development of computer interfaced optical microscopy. This is followed by a description of how our methods of fluorescence, interferometry and stereology, nsed for characterizing polymeric foams, have incorporated computers. 

In general, flow cytometry is an optical analytical method to characterize cells or particles in suspension. Accordingly, a flow cytometer is simply described as a specialized fluorescence microscope equipped with a quantitative high-throughput detector system to measure various cellular parameters [33-35],... 

Cracks were observed on the top surface and the section surface of the disk with an optical microscope. The microstructure was observed by SEM. The surfaces were polished with diamond paste. The Vickers indentation technique was used to evaluate the direction of residual stress. The residual stresses were calculated by an analytical technique on the assumption of elastic condition [2]. For electrical measurement, Pt electrode was formed on the disk surfaces with Pt paste. The electrical resistivity was measured by two-probe method. 

No convincing conclusion has been reached as to the biodegradation mechanisms of bioactive ceramics. Many researchers have reported different results, as described above. These discrepancies are considered to be caused by the fact that materials used for the experiments were different, and that experimental methods and analytical methods were also different. Therefore, when these reported results are compared, it is important to consider the characteristics of the material used (chemical compositions, impurity, crystallinity, dense or porous, micro- or macro-porous, porosity), experimental methods used in vivo or in vitro, animal species, implanted duration, implanted sites, load bearing or not), and analytical methods used (radiographic, optical microscopic, electron microscopic). Futhermore, a good understanding of the characteristics of the materials to be used becomes important when bioactive ceramics are used clinically. 

There are no standard tests for measuring the onset of asphaltenes precipitation. Among the techniques and analytical methods frequently used to measure sediment and asphaltenes onset for the adjustment of different process parameters in the refineries are spot test (ASTM-D-4740-95) total sediment (ASTM-4870-96) solubility parameters, optical microscope light scattering (PORLA) peptization value (P-value) ° colloidal instability index (CII) coking index. ... 

The characterizahon of nanosilica incorporates many convenhonal microscopic and analytical methods. The details of such methods, the parameters that can be determined with them, and the associated references are summarized in Table 2.2. The main parameters to be identified are the morphology, surface characterizahon and measurement of optical properties of either the sihca core or the surfactants. Although, in order to produce specific nanosilica, a good knowledge of these methods and other novel techniques is clearly required, they will not be described in great detail at this point. 

Physical and chemical characterization methods are essential to assess aspects such as material and processing quality. Raman microprobe is an analytical tool coupled to an optical microscope. Elemental analysis using the x-rays emitted from the specimens in the electronic microscopy techniques can be used for local composition determination or to obtain a map of the distribution of a certain element in a wider area wavelength and energy-dispersive x-ray spectrometers are used for these purposes. Fourier transform infrared spectrometer is widely used for the qualitative and quantitative analysis of adhesives, the identification of unknown chemical compounds, and the characterization of chemical reactions. Thermal methods such as thermomechanical analysis and differential scanning calorimetry are discussed as valuable tools for obtaining information during postfracture analysis of adhesively bonded joints. 

To assess homogeneity, the distribution of chemical constituents in a matrix is at the core of the investigation. This distribution can range from a random temporal and spatial occurrence at atomic or molecular levels over well defined patterns in crystalline structures to clusters of a chemical of microscopic to macroscopic scale. Although many physical and optical methods as well as analytical chemistry methods are used to visualize and quantify such spatial distributions, the determination of chemical homogeneity in a CRM must be treated as part of the uncertainty budget affecting analytical chemistry measurements. 

Infrared (IR) spectroscopy, especially when measured by means of the Fourier transform method (FTIR), is another powerful technique for the physical characterization of pharmaceutical solids [17]. In the IR method, the vibrational modes of a molecule are used to deduce structural information. When studied in the solid, these same vibrations normally are affected by the nature of the structural details of the analyte, thus yielding information useful to the formulation scientist. The FTIR spectra are often used to evaluate the type of polymorphism existing in a drug substance, and they can be very useful in studies of the water contained within a hydrate species. With modem instrumentation, it is straightforward to obtain FTIR spectra of micrometer-sized particles through the use of a microscope fitted with suitable optics. 

Probably the most extensive use of particle morphology and microscopy has been in the area of chemical microscopy. With this approach, derivatives of the analyte species are prepared, crystallized, and identified through the morphological characteristics of these derivatives [21]. Most of these applications have been superseded by modem methods of analysis, but the microscopic method can still be used by skilled practitioners for the study of trace quantities of analyte. The literature developed during the heyday of chemical microscopy is too large to be reviewed here, but advances in the field are still chronicled in the Annual Reviews issue of Analytical Chemistry [22]. A substantial review of the optical characteristics of organic compounds is available [23]. 

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