Isomer-selective and enantiomer-selective determination of DDT and related compounds using chiral high-resolution gas chromatography/mass spectrometry and chiral HPLC.

Abstract

The composition of technical DDT was investigated using achiral and chiral high-resolution gas chromatography (HRGC) and electron-ionization mass spectrometry (EI-MS). 2,4'-DDT and 2,4'-DDD, two important components of technical DDT, were enantiomerically resolved by chiral HRGC with silylated β-cyclodextrin and by chiral high-performance chromatography (HPLC) with permethylated γ-cyclodextrin as chiral selectors. The (+)- and (-)-enantiomers were assigned by chiral HPLC using chiroptical measurements. Enantiopure isolates were then used to identity these enantiomers in chiral HRGC analyses. Previous data indicated (+)- and (-)-2,4'-DDT to have Sand R-configuration, respectively, but the absolute configurations for (+)- and (-)-2,4'-DDD were hitherto unknown. They were now assigned via the reductive dechlorination of the individual 2,4'-DDT enantiomers which proceeded stereoselectively to the corresponding 2,4'-DDD enantiomers. The results showed (+)- and (-)-2,4'-DDD to have R- and S-configuration, respectively. The enantiomers of 2,4'-DDD thus have reversed signs of rotation for polarized light compared to the enantiomers of 2,4'-DDT with the same configuration. The enantiomer resolution of several additional chiral compounds in technical DDT is reported ; enantiomeric ratios of 1.0 indicated all chiral compounds to be present as racemates in the technical and in the synthetic reference materials. We report the first enantioselective determinations of technical DDT ; the methods presented should also be applicable to the analysis of environmental and biological samples.