Technique for Establishing Baseline in Infrared Spectrometry

Abstract

The determination of the shape and intensity of an infrared absorption band is complicated by the difficulty of establishing the zero absorbance (100% transmittance) baseline to which the absorption band may be related. For example, the choice between a Gaussian or Cauchy distribution function as a model for the absorption band is particularly affected because these functions differ most significantly in ordinate at distances greater than about one-half-bandwidth from the band center, where the relative error in transmittance will also be the largest.¹ The use of blanks for determining the zero-absorbance line (either empty cells or cells filled with pure solvent) is of limited value, particularly in infrared spectroscopy, because of the variations in refractive index of the solution at different concentrations of solute and the resultant variations in reflection losses at the cell-solution interfaces.