Observation of a Penetration Depth Gradient in ATR FT-IR Spectroscopic Imaging Applications

4 Observation of a Penetration Depth Gradient in ATR FT-IR Spectroscopic Imaging Applications 

For homogeneous samples, it would be possible to correct this gradient mathematically. However, for heterogeneous samples, which are mostly analyzed with IR imaging, this is hardly possible due to the large influence of the different refractive indices, which would have to be taken into consideration. 

Generally, for a qualitative analysis of heterogeneous samples the results will hardly be influenced by this phenomenon. For quantitative analysis, however, the effect must be taken into account. By using another reflection element, for example, germanium with a higher refractive index (4.0 instead of 2.4 for ZnSe), the gradient would be much smaller (about one-third), because of the lower penetration depth under these experimental conditions. 

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