The need for 2-D correlation in NIR spectroscopy

Abstract

Two-dimensional (2-D) vibrational correlation spectroscopy has now advanced to the stage of realizing many of its touted advantages. Those advantages primarily are: elucidation of chemical interactions of functional groups, simplification of complex spectra, enhancement of spectral resolution by spreading over the second dimension and establishing unambiguous assignments through cross-correlation. Three basic methods have been employed to attain these advantages: dynamical correlation, statistical correlation and canonical correlation analysis. The most popular of these has been dynamical correlation which requires a perturbation due to some stimulus that results in time-dependent fluctuations of spectra. These types of correlations may be applied to almost any form of spectroscopy, yet they have mostly been applied to what may be considered to be forms of high resolution spectroscopic methods, NMR and mid-infrared (MIR) spectroscopy. However, their usage is even more necessary in low resolution forms of spectroscopy. Near-infrared (NIR) spectroscopy is a good example of such a low resolution form for which 2-D correlation spectroscopy is almost required in order to understand the interactions of fundamental vibrations originating in the MIR region. Also, NIR bands often display anharmonic effects making band assignments extremely difficult. There have been limited applications of 2-D correlation to NIR spectroscopy, but there is a need for many more. The results of some applications will be discussed, along with the future potential of this technique in NIR spectroscopy.