Microwave Assisted Extraction of Dioxins and Furans Compared to Soxhlet

Microwave assisted extraction (MAE) offers significant benefits over traditional soxhlet extraction for dioxins and furans determination from environmental samples including higher sample throughput, time savings, reduced solvent and great reproducibility.

Polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are groups of polyhalogenated compounds found as environmental pollutants resulting from a number of manufacturing processes, and have been linked to a number of human biological disorders through accumulation in fat tissue. PCDDs and PCDFs can be formed by pyrolysis, or incineration at high temperatures, of chlorine containing products such as PVC, PCBs, and other organochlorides.

Soxhlet is the traditional approach for extracting PCDDs and PCDFs from environmental soils, sludges, and other matrices. Although effective, soxhlet extraction requires large amounts of solvent and takes hours to complete. Alternatively, microwave extraction, using approved EPA method 3546, provides a fast and reproducible method without the high solvent consumption. PCDD/PCDF recoveries by MAE are equivalent or better than soxhlet.

Experimental Conditions

MAE using Milestone's Ethos EX was compared to soxhlet extraction for dioxins and furans extraction from fly ash. The Ethos EX labstation can extract 24 samples simultaneously in a closed vessel system. With increased pressure capabilities, temperatures above the boiling point of the solvent are used to decrease the extraction time to 45 min with 30 mL of solvent per sample. The closed vessel system along with magnetic stirring for constant agitation, direct temperature monitoring, and the ability to reuse stored methods allows for great reproducibility of dioxins and furans recoveries.

Table I: GC-MS recovery results from microwave assisted and soxhlet extraction

For the MAEs, 2 g of fly ash were weighed into a microwave vessel. A stir bar, a carbon coated weflon button (for absorbing microwaves when using non-polar solvents), and 30-mL of toluene were added to the vessel. Extractions were completed at 140 °C with a total program time of 45 min. For soxhlet, the extractions took 24 h to complete using 150 mL of solvent. Both extracts were analyzed by GC–MS using an Agilent J&W DB-5ms column.

Results

Extraction rates with Milestone's Ethos EX are 32 times faster, with recoveries comparable or better than traditional soxhlet, and 500% or greater reduction in solvent required.

Conclusions

Milestone's Ethos EX successfully extracted dioxins and furans from fly ash in just 45 min with very little solvent. As the results show, MAE yields comparable or better results than soxhlet extraction. The ability to perform 24 samples simultaneously is ideal for high throughput labs looking to save space, time, and money while getting great recoveries of dioxins and furans.

Milestone Inc.

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