Selective and sensitive analysis by reactive easy ambient sonic-spray ionization: Synergistic combination of non-polar spray solvent and dicationic ionic liquid.

The present study reports the first conception to incorporate a non-polar solvent, dichloromethane, as the spray solution in easy ambient sonic-spray ionization (EASI) for mass spectrometry (MS) analysis of hydrophobic compounds. An imidazolium-based dicationic ionic liquid (DIL) at a low concentration of 20 μM was used in combination with dichloromethane. A reactive EASI strategy was implemented, by which the overall positively charged associated complexes of anionized perfluorinated compounds (PFCs) were formed in the presence of the DIL. In positive ionization mode, 19- and 6-fold enhancements in signal intensity were witnessed for the analysis of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) respectively, compared to that in negative ionization mode with no dicationic ion-pairing reagent. The limits of detection (LODs) and quantitation (LOQs) are 0.5 and 0.8 μg/m for PFOA and 0.4 and 0.6 μg/m for PFOS, respectively. The developed method allowed direct ambient analysis of samples in their native conditions and was applied to the analysis of PFCs in a variety of real textile, popcorn bucket, and oil-proof hamburger wrapping paper samples.