Untitled

Abstract

Transferring a multivariate model between infrared spectrometers is a significant challenge, and current methods often require the creation of costly standard samples to ensure sufficient accuracy. A good solution would be to first convert the measured spectra to k spectra (also called extinction coefficient spectra, imaginary refractive index spectra or absolute absorbance spectra). Unlike an absorption or transmission spectrum, which depends on the spectrometer used, the k spectrum is a property of the material, and this would make it an ideal standardized form for infrared spectra. In theory, this would allow models based on k spectra to be directly used for k spectra from other spectrometers.The feasibility of this idea was tested by calculating and comparing the k spectra from two different spectrometers for pure compounds and shale oil samples. Although deviations between spectra from the two spectrometers were reduced, significant differences still remained. Further analysis indicated that the likely cause of these differences was misalignment in the optics of the spectrometers. Some amount of misalignment is common in spectrometers, and the current method for calculating k spectra does not directly account for this. Therefore, further research needs to be done to adequately correct for misalignment to obtain accurate k spectra.