Comprehensive profiling of 136 tetra- to octa-polychlorinated dibenzo-p-dioxins and dibenzofurans using ionic liquid columns and column combinations

Abstract

The orders of elution of all 136 tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were determined on six gas chromatography (GC) columns. Three of these columns had ionic liquid stationary phases (SLB-IL111, SLB-IL76 and SLB-IL61; Supelco), one a liquid crystal phase (LC-50; Restek), one a chiral phase (βDEXcst; Restek) and one a low bleed non-polar phase (DB-XLB; J&W/Agilent). According to our results, the high polarity and multiple solvation interactions of the ionic liquid stationary phases offered superior resolving power to that achieved with previously evaluated columns. The SLB-IL61 and SLB-IL111 columns resolved or partially separated 106 and 100 congeners, respectively, of the 136 PCDD/Fs. The SLB-IL61 also resolved 15 and partially separated one of the seventeen 2,3,7,8-substituted PCDD/Fs. Additional congeners can be separated by complementary analyses using additional columns in a dual- or triple-column approach. For example, using a combination of the SLB-IL61 and SLB-IL111 columns all but 8 congeners would be separated, including all 2,3,7,8-substituted PCDD/Fs. Two more congeners would be separated using a combination of SLB-IL76 and a liquid crystal (SB-Smectic) column, but in this case the 2,3,7,8-TeCDF would not be resolved. Three-column combinations would give even better separation: the DB-17/Smectic/SLB-IL76 and DB-225/Smectic/SLB-IL111 combinations would separate all but 1 of the 136 PCDD/F congeners. Unfortunately, the smectic column is no longer in production. If only commercially available columns are considered, combinations of SLB-IL61 and SLB-IL111 with DB-XLB, LC-50, or DB-225 offer the best performance, with 4, 4, and 3 unresolved congeners, respectively. Moreover, in each of these cases, one of the congeners in each unresolved pair is resolved on at least one of the other columns and so a reasonable estimate of the unresolved congeners' concentrations can be obtained by subtraction. The profiling of all 136 PCDD/Fs is thus greatly facilitated by using ionic liquid columns or combinations including such columns. However, there is room for improvement in the technical performance of the evaluated ionic liquid columns: their long-term retention time stability was poor and some highly chlorinated and sterically hindered congeners underwent dehalogenation during separation.

Keywords: Column combination; Dioxins; Furans; Gas chromatography; Ionic liquids.