Capture of air particulate matter and gaseous Hg0 by ionic liquids analyzed by PIXE

Particle induced X-ray emission (PIXE) has been extensively employed to study the elements associated to air particulate matter (PM). However, the atmosphere is a very complex system and inorganic pollutants may be also in gaseous phases. Aerosol monitoring does not allow the determination of all the volatile inorganic compounds, since they are not retained in the filters, or if they are trapped, the analysis under vacuum results in a partial or total loss of them. In order to extend the applications of PIXE there is a need to develop new methods to simultaneously capture particulate matter and volatile substances. Ionic liquids (IL) result from combinations of organic cations and anions that may be liquid at room temperature. The physicochemical characteristics of ILs allow them to absorb atmospheric trace metals present in solid and gaseous phases, a task normally performed with independent sampling methods. In this work we explored this capability of ILs as monitors of chemical species which can be found in the gas phase and as particulate matter. The tested ILs included 1-Butyl-3-Methyl-Imidazolium-Hexafluorophosphate [BMIM][PF 6 ] for PM and Hg capture; and 1-Butyl-3 methylimidazolium thiocyanate [BMIM][SCN] only for Hg capture. Elemental analysis of both experiments was performed by Particle Induced X-ray emission (PIXE). Changes in the molecular structure on BMIM PF 6 due to the Hg binding were followed by infrared (IR) spectroscopy. [BMIM][PF 6 ] proved to be successful as passive collector of PM. However when both were used for Hg capture, [BMIM][SCN] showed better selectivity. These preliminary results showed the potential of IL’s for simultaneous uptake of PM and volatile inorganic compounds.