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The diffuse reflectance spectroscopic technique provides a convenient means of obtaining mid-infrared spectra of soils, as an alternative to the pressed halide disc method. Advantages and drawbacks of the DRIFT technique are discussed and compared with those for the KBr pressed disc method for a range of Australian soils. Useful sample concentrations for DRIFT spectra range from 1-100%, i.e. much higher than for typical pressed halide discs. This high sample concentration leads to an apparent enhancement of relatively weak band intensities, providing increased information content for soil characterization. Some neat soils and soil minerals, however, show severe distortion of strongly absorbing bands at high sample concentrations, generally at frequencies below 1100 cm-1. This results in some bands having an 'inverted' appearance. Bands due to organic components are clearly visible in the range 3100-2800 cm-l. Mineral components of soils often show a group of broad, weak-medium intensity bands in the 2600-1650 cm-1 region due to overtone and combination vibrations. These bands, enhanced in DRIFT spectra, are useful for characterization purposes. For example, bands in the region near 2600-2500 cm-1 are diagnostic features for the identification of calcite and dolomite, while those in the region 2000-1650 cm-1 are characteristic of quartz and kaolinite.
Nguyen et al. (Fri,) studied this question.