Analytical Accuracy in Unpolarized ATR Spectroscopy: Effects of the Spectrometer Polarization Ratio

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Abstract
A method for the determination of the wavelength-dependent polarization ratio [PR(λ)] for any spectrometer is described. Equations are also developed for an averaged effective thickness for use in analyses of unpolarized ATR spectra, and for parallel and perpendicular effective thicknesses for use with external polarizers of known efficiency. Polarization ratios for one Fourier transform IR spectrometer and one grating IR spectrometer are presented and compared. In unpolarized ATR spectrophotometry using the grating spectrometer, the assumption of PR = 1.0 for all wavelengths introduces a Beer's law pathlength uncertainty of approximately a factor of 1.8.