HPLC Separation and FT-IR Isomer Differentiation of the 1,2,4,7/1,2,4,8-Tetrachlorodibenzodioxin Isomer Pair—A Theoretical/Empirical Approach to Dibenzodioxin Isomer Assignment

Abstract

The 1,2,4,7- and 1,2,4,8-tetrachlorodibenzodioxin (TCDD) isomers were separated by reversed-phase high-performance liquid chromatography (HPLC) with the use of a pyrene column. Fourier transform infrared (FT-IR) matrix isolation and vapor-phase spectra of the individual isomers were recorded. The spectra of the HPLC-separated isomers correlate well with spectral subtraction results and were found to be distinct in three spectral regions—one of which allows for isomer structural assignment. Ambiguities and differences in published TCDD isomer FT-IR assignments are discussed in terms of a qualitative valence-bond approach and empirically derived estimates of ether linkage asymmetric stretching frequencies.