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Diffuse reflectance infrared Fourier transform spectroscopy
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<p>Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is an <a href="/facts/Infrared_spectroscopy/u1Hzx617">infrared spectroscopy</a> sampling technique used on powder samples without prior preparation. The sample is added to a sample cup and the data is collected on the bulk sample. The infrared light on a sample is reflected and transmitted at different amounts depending on the bulk properties of the material. <a href="/facts/Diffuse_reflection/wG9w4tAX">Diffuse reflection</a> of the incident light produced by the sample's rough surface reflection in all directions is collected by use of an ellipsoid or paraboloid mirror. Shape, compactness, <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a>, <a href="/facts/Reflectivity/TT4sBwIw">reflectivity</a> and absorption of the particles are all characteristic of the material being analyzed. If the sample is too absorbent, then it can be diluted with a nonabsorbent material such as <a href="/facts/Potassium_bromide/mGWPW1zd">potassium bromide</a>, <a href="/facts/Potassium_chloride/RgT2MdPa">potassium chloride</a>, etc. The particle size should be smaller than the wavelength of the incident light in order to minimize <a href="/facts/Mie_scattering/5mJc3SrT">Mie scattering</a>, so this would infer that it should be less than 5 <a href="/facts/%25CE%259Cm/7eDFxD2L">μm</a> for mid-infrared spectroscopy. The spectra are plotted in units of log inverse reflectance (log 1/R) versus wavenumber. Alternative plots of Kubelka-Munk units can be used, which relate reflectance to concentration using a scaling factor. A reflectance standard is needed in order to quantify the reflectance of the sample because it cannot be determined directly. </p>