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.

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.