Resolution of overlapping mid-infrared spectra using SIMPLISMA and a second-order derivative approach

Matrices of severely overlapping mid-infrared mixture spectra have been resolved into the pure compounds' spectra and concentration profiles using SIMPLISMA and a 2nd order derivative approach. For a three-compound mixture system of organic solvents, SIMPLISMA qualitatively resolves the spectra satisfactorily while it provides only semi-quantitative concentrations. Quantitative results are obtained by applying an additional iterative procedure. Applied to water spectra acquired in the temperature range 2-96 degrees C, SIMPLISMA resolves two spectra. Using a discrete model, these spectra can be interpreted as corresponding to water structures constructed of H2O molecules with a relatively high and low average number of H-bonds. After an optimising procedure the estimated enthalpy was 2.3 kcal mol(-1), which is in accordance with figures found in literature.