This paper introduces a new approach to analysis of spectra called asynchronous orthogonal sample design (AOSD). Specifically designed concentration series are selected according to mathematical analysis of orthogonal vectors. Based on the AOSD approach, the interfering portion of the spectra arising strictly from the concentration effect can be completely removed from the asynchronous spectra. Thus, two-dimensional (2D) asynchronous spectra can be used as an effective tool to characterize intermolecular interactions that lead to apparent deviations from the Beer–Lambert law, even if the characteristic peaks of two compounds are substantially overlapped. A model solution with two solutes is used to investigate the behavior of the 2D asynchronous spectra under different extents of overlap of the characteristic peaks. Simulation results demonstrate that the resulting spectral patterns can reflect subtle spectral variations in bandwidths, peak positions, and absorptivities brought about by intermolecular interaction, which are barely visualized in the conventional one-dimensional (1D) spectra. Intermolecular interactions between butanone and dimethyl formamide (DMF) in CCl<sub>4</sub> solutions were investigated using the proposed AOSD approach to prove the applicability of the AOSD method in real chemical systems.
Xiaopei Li, Qinghua Pan, Jing Chen, Shaoxuan Liu, Anqi He, Cuige Liu, Yongju Wei, Kun Huang, Limin Yang, Juan Feng, Ying Zhao, Yizhuang Xu, Yukihiro Ozaki, Isao Noda, and Jinguang Wu, "Asynchronous Orthogonal Sample Design Scheme for TwoDimensional Correlation Spectroscopy (2D-COS) and Its Application in Probing Intermolecular Interactions from Overlapping Infrared (IR) Bands," Appl. Spectrosc. 65, 901-917 (2011)