2-DIMENSIONAL VIBRATIONAL SPECTROSCOPY .2. CORRELATION OF THE ABSORPTIONS OF LIGNINS IN THE MIDINFRARED AND NEAR-INFRARED

Two-dimensional (2D) statistical correlation of mid- and near-infrared spectra was used as a means to assist with qualitative spectral inter pretation of the lignin carbohydrate fractions from plant materials. C ross-correlation by least-squares is used to assess changes in both re gions that result from changes in the set of sample spectra. The techn ique has been applied to a set of specially prepared ''lignin'' sample s that differ in lignin content, species of origin, and method of prep aration. Dispersive near-infrared (NIR) and Fourier transformed mid-in frared (FT-IR) diffuse reflectance spectra (DRIFTS) were obtained on e ach of the samples, and point-for-point 2D cross-correlation was obtai ned. The technique permits the correlation of the combination and over tone bands of the NIR region with the fundamental vibrations in the mi d-infrared (MIR) region. The results show a broad correlation of aroma tic C-H stretch at 3022 cm-1 in the MIR to 1666-nm location in the NIR region and other locations to a lesser extent all across the NIR from 1400 to 2500 nm. A narrower region of correlation was found for the p henolic O-H stretch in the MIR at 3663 cm-1 to 1428 nm and 1938 nm in the MIR. Multiple narrow correlations occur in the area of the summati on bands from 1450 to 1650 cm-1, indicative of substitution patterns a nd correlated areas of C-H and O-H stretch in the NIR.