Infrared Spectroscopy Questions and Answers

Answer: A

The first three are correct and the fourth is badly wrong: sodium chloride dissolves in water, which is why infrared work with aqueous samples is so awkward and why attenuated total reflectance with a diamond or zinc selenide crystal is used instead. That the cheapest and most transparent window material is unusable with the most important solvent is one of the defining practical constraints of the technique.

Answer: B

This is attenuated total reflectance, named because the reflection is weakened wherever the sample absorbs. Diffuse reflectance is a different technique for powders, specular reflectance measures light bounced off a polished surface, and polarised work uses oriented samples. Four reflectance techniques with four quite different geometries, and each suits a different kind of sample.

Answer: C

Greater sensitivity is not among them - the effective path is only micrometres, so the technique is markedly less sensitive than a transmission cell. The other three are genuine advantages, and the reproducible path length in particular makes quantitative work possible where a mull or pellet could not. A technique adopted despite a loss of sensitivity is one whose other advantages must be substantial, and here they are.