Advances in Two-Dimensional Correlation Spectroscopy (2DCOS)

A tutorial for generalized two-dimensional correlation spectroscopy (2DCOS) is provided to show how this technique can be applied to a wide range of spectroscopic and other analytic problems. In generalized 2DCOS, similarity or dissimilarity among variations of spectroscopic intensities, which are induced by applying an external perturbation to the sample system, is examined by constructing correlation spectra defined by two independent spectral variable axes. By spreading congested or overlapped peaks along the second dimension, apparent spectral resolution is enhanced, and interpretation of complex spectra becomes simplified. A set of simple rules for the intensities and signs of correlation peaks is used to extract insightful information. Simulated model spectra and experimental IR spectra obtained during the melt crystallization of a biodegradable copolymer are used to demonstrate the utility of 2DCOS. Additional tools useful in 2DCOS analysis, such as 2D heterocorrelation, moving-window analysis, codistribution analysis, Pareto scaling, and null-space projection, are also discussed with illustrative examples.