Friday, November 22, 2019

Why are salt plates used in IR rather than glass?

Sodium chloride (NaCl) cells are transparent to IR and do not absorb the infrared radiation in the region between 4000-450 cm-1; hence it is used to analyze the sample in IR. When analyzing the IR spectra the glass or quartz cells cannot be used because it absorbs IR radiation. Liquid samples are often cleaned between NaCl salt plates. As solvents absorb IR radiation, IR cells typically have narrow path lengths to maintain solvent absorption to adequate levels. Solid samples are often prepared by potassium bromide (KBr) in pellet form in the hydraulic pellet press. Nowadays Attenuated total reflectance spectroscopy (ATR) is another characteristic application for determining the functional group of molecules. It doesn’t need to prepare samples. This facilitates samples to be analyzed directly in solid, liquid, gel, or powder state without any preparation.


 

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