Fig. 5

a A comparison of the sampling when powders and liquids are placed in contact with an ATR crystal. In the case of powered samples, there is a challenge in creating a close enough contact to ensure sufficient absorption of IR light since the particles may be loosely packed creating air gaps. Finer powders mitigate this issue as smaller particles can pack closer. b The wavelength dependence of the IR penetration depth further complicates the various packing scenarios, and ultimately affects the mixture analysis