Investigation of Optically Dense Systems by Internal Reflection Spectroscopy: Experimental Considerations
Many materials of importance in natural waters and waste-water systems—e.g., sediments, suspensions, and precipitates—are optically opaque. The application of transmission spectroscopy for purposes of analysis and identification of such materials is therefore usually precluded. For cases in which conventional transmission spectroscopy is not feasible because of scattering effects and/or extensive attenuation of incident light, the technique of internal-reflectance spectroscopy (IRS) often provides a means for obtaining characteristic spectral data. Several specific examples are presented to indicate that IRS provides high contrast spectra comparable to the best transmission spectra for “clean” systems, provided appropriate IRS geometry, components, and techniques are selected. Examples include active carbons and carbon blacks, marine sediments, freshwater sediments, and extremely turbid suspensions. Experimental considerations involved in the application of IRS to such systems are discussed. Interpretation of IRS spectra, and the differences to be expected between IRS and transmission spectra are also considered.
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