A solvent recirculation trapping device for supercritical fluid extraction of polyaromatic hydrocarbons.

A new device has been developed for the trapping of volatile pollutants in trapping solvents. The device allows solvent recirculation and cryogenic trapping of evaporated volatiles to minimize the stripping effect and any losses of volatile analytes. Due to solvent recirculation, the trapping solvent column height remains constant during the extraction without any need for replenishment. Also mass transfer conditions are favorable due to the flattened shape of bubbles of CO2 and the longer extraction time. The bubbles have higher interfacial area and they have to pass a three times longer distance in the solvent column. The device produces more concentrated extracts, reduces solvent consumption, and reduces or eliminates its evaporation to the environment. The cryotrapping part reduces losses of volatile analytes and the stripping effect. It also enables single-phase extraction into much smaller solvent volumes. Due to constant and favorable extraction conditions, the precision of the method was also greatly improved (RSDs decreased from 2.2 to 0.8%). As proved by a set of rapid spiked-sample extractions of highly volatile compounds at very high flow rates, the relative standard deviation of the experiments performed in the new device is 3.5 times lower.