Solids, infrared spectrophotometry

Various techniques are available for the investigation of the solid state. These include microscopy (including hot-stage microscopy, HSM), infrared spectrophotometry (IRS), single-crystal X-ray and X-ray powder diffraction (XRPD), thermal analysis, and dilatometry. 

R. S. Browning, S. E. Wiberley, and F. C. Nachod, Application of Infrared Spectrophotometry to Quantitative Analysis in the Solid Phase, Anal. Chem. 27, 7, 1955. 

Combination of thermogravimetry and infrared spectrophotometry for observing solid... 

Examine by infrared absorption spectrophotometry comparing with the spectrum obtained with nimodipine CRS. If the spectra obtained in the solid state show differences, record further spectra using 20 g/L solutions in methylene chloride R and a 0.2-mm cell. 

Various techniques have been applied in studies of solid samples. A direct method based on infrared spectroscopy has been used in the study of pharmacologically active compounds such as nitroimidazole derivatives (chemotherapeutics) and nifedipine (Marciniec and Rychcik, 1994 Marciniec et al., 1997). This approach can be applied in kinetic and quantitative examinations of the degradation process. An alternative method based on diffuse reflectance spectrophotometry takes into account the surface reflectance of the sample (Zhan et al., 1995). In recent years, Raman spectroscopy has become a powerful tool for the study of various processes in the solid state. The technique allows mapping of the concentration of one specific component within a sample, e.g., an active ingredient in a tablet formulation. This method may therefore become a useful tool in future studies of solid-state photodegradation (Opel and Venturini, 2002). 

Chemical analysis of hazardous substances in air, water, soil, sediment, or solid waste can best be performed by instrumental techniques involving gas chromatography (GC), high-performance liquid chromatography (HPLC), GC/mass spectrometry (MS), Fourier transform infrared spectroscopy (FTIR), and atomic absorption spectrophotometry (AA) (for the metals). GC techniques using a flame ionization detector (FID) or electron-capture detector (BCD) are widely used. Other detectors can be used for specific analyses. However, for unknown substances, identification by GC is extremely difficult. The number of pollutants listed by the U.S. Environmental Protection Agency (EPA) are only in the hundreds — in comparison with the thousands of harmful... 

One good thing about this new method is that it is performance based. The analyst can use an alternative approach to oil and grease isolation and recovery. One approach is to use solid-phase extraction (SPE) to isolate the oil and grease, whereas the other approach is to find a way to eliminate use of the solvent. The recently introduced use of infrared cards by 3M Corporation, whereby the oil and grease remains on a thin film of Teflon, is an example of the latter alternative to the conventional liquid-liquid extraction (LLE). The thin film that now offers a fixed path length, is then inserted into the sample holder of a conventional infrared spectrophotometer and the absorbance of the C — H stretching vibration at 2900 cm is directly related to concentration via the Beer Lambert Law of Spectrophotometry discussed in Chapter 4. 

The spectrophotometry is a technique based on Lambert-Beer law, which is the math support for measurement of the absorption of radiation by solid, liquid, or gaseous samples. The absorption can occur in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum [21]. 

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