The alternative to using KBr in IR spectroscopy is the use of a diamond crystal. Diamond is a transparent material with a high refractive index and is chemically inert, making it a suitable substrate for FTIR (Fourier Transform Infrared) analysis.
KBr (potassium bromide) is commonly used in IR spectroscopy for sample preparation. It is used to mix the sample and obtain accurate IR spectra with sharp peaks, good intensity, and high resolution. KBr is typically used in pellet form, where the powdered sample is dispersed in KBr and compressed into a disc.
To prepare a KBr pellet, the sample is mixed with a fine KBr powder in a specific ratio (usually 100:1 KBr to sample by weight). The mixture is then finely pulverized and put into a pellet-forming die. A force of approximately 8 tons is applied under vacuum for several minutes to form transparent pellets. This process degasses the KBr powder, eliminating air and moisture. Insufficient vacuum can result in easily broken pellets that scatter light. Before forming the KBr powder into pellets, it is pulverized and dried to remove any moisture. After drying, the powder is stored in a desiccator.
During measurements, a background measurement is taken with an empty pellet holder or a pellet holder containing only KBr. This measurement corrects for infrared light scattering losses in the pellet and for moisture adsorbed on the KBr.
It is important to note that KBr is hygroscopic, meaning it absorbs moisture from the air. This can affect the FTIR measurement, especially in humid environments or with long exposure times. To minimize moisture absorption, grinding and pressing can be performed in a glovebox or with a vacuum die.
In summary, the alternative to KBr in IR spectroscopy is the use of a diamond crystal. However, KBr is commonly used for sample preparation in IR spectroscopy by mixing the sample with KBr powder and compressing it into pellets. The KBr pellets allow infrared light to pass through, providing accurate IR spectra.
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