Selection of the internal reflection element

The IRE material must show transparent regions in the infrared and it should have a proper refractive index to allow internal reflection. It must be insoluble in the usual solvents and chemical inert to all components in the sample. However, from the list of IR-transparent materials in Table 3.4-1 only a few are recommended for IRE s. Table 6.5-1 lists most of these materials. 

Of the large number of possible IRE shapes (Harrick, 1979) only few are usually used for the membrane method. Their shapes are like a trapezoid or parallelepiped. Cylindrical IRE with conical ends (Tunnel Cell, Circle Cell (Doyle, 1990)) and even optical fibers are also possible. 

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