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2.3 Common Sampling Modes

There are many techniques for the measurement of IR spectra. The basic ones utilize the fact that the alkali salts are transparent in large portions of the IR part of the electromagnetic spectrum. This section briefly summarizes some of the common techniques.

KBr pellet
good for powders; a few milligrams of the sample power and an excess of KBr are finely ground and pressed under high pressure into a pellet. This is a useful and very general method for solids.
Salt cells:
good for organic liquids; the liquid is placed into a reservoir milled in alkali salt windows.
Nujol mull:
the material of interest is suspended in oil, such as mineral oil, and the resulting paste is spread thinly on a salt window to form a film. This is a good technique for oils and waxy solids that do not press well into pellets.

John S. Riley, DSB Scientific Consulting