Corrections to the Baseline Distortions in the OH-Stretch Region of Aqueous Solutions

The intensity gains or intensity losses of the OH-stretch vibrations and their changes of band shapes as observed in IR or Raman spectra of dilute aqueous solutions of carboxylic acids, amino acids, and amines were able to be simulated. The difference spectra of the type {sample solution} – {standard} x {empirical factor} displayed essentially flat baselines throughout the OH-stretch region of isotropic Raman scattering. Peaks of the solute spectra which had been hidden by the OH-stretch contour emerged from the background. At concentrations below 1 M, pure water was the standard. Distortions of the isotropic Raman spectra at higher solute concentrations (1 M to 4 M) could be mimicked by phosphoric acid or sulfuric acid solutions as standards. The influence of solutes on the reorientational motions of water molecules made baseline corrections of anisotropic Raman scattering and IR absorption of the more concentrated solutions difficult, if not impossible.