Correction of distorted ATR infrared spectra

During the last decade, there has been a significant increase in the use of attenuated total reflection (ATR) infrared spectroscopy because of its experimental simplicity and nondestructive nature. However, when samples with a high refractive index, like black carbon, are analyzed, their spectra will appear significantly distorted. In this case the data evaluation is challenging and the spectra need to be corrected. In the present study, we use the fast Kramers-Kronig transform and related mathematical methods to achieve fast correction of the distorted spectrum. Our results show that interpreting the data without appropriate correction can lead to false conclusions. For example, peaks, which appear to be red-shifted in the distorted raw spectrum, may actually be blue-shifted. Furthermore, we demonstrate the application of our method to heterogeneous samples consisting of inorganic powders and organic liquids. Taking Snell’s law into consideration, the relationship between the real and imaginary parts of the complex refractive index can be obtained when the angle of incidence is below a critical value. This can be exploited for a quantitative analysis.