Direct Mass Spectrometry Analysis Using In-Capillary Dicationic Ionic Liquid-Based in Situ Dispersive Liquid-Liquid Microextraction and Sonic-Spray Ionization.

The current study reports on a direct mass spectrometry (MS) analysis method using in-capillary dicationic ionic liquid (DIL)-based in situ dispersive liquid-liquid microextraction (DLLME) and sonic-spray ionization (SSI). The developed method merged extraction, enrichment, ionization, and detection of perfluorinated compounds (PFCs) in environmental water into a single step. A microliter-scale ternary fluidic system was designed and integrated into a disposable pulled capillary, in which an imidazolium-based germinal DIL reagent activated an in situ metathesis reaction. A penetrating slug-flow microextraction (SFME) process was subsequently initiated with significantly enhanced interfacial areas and mass transfer rates for the analytes of interest, the mechanism of which was revealed by simulations. An SSI assembly was in-house built, and it enabled a Venturi self-pumping using a stream of nitrogen gas flow coaxial to the capillary under atmospheric pressure to automatically spray at the tip of the capillary. The in situ formed DIL could bind with anionic PFC analytes to generate a positively charged complex, which benefits a signal increase of 1 to 2 orders in magnitude in the positive ion mode than in the negative ion mode for most analytes. The high sensitivity allowed the measure of sub-ppb (parts per billion) levels of PFCs in the environmental water samples. The developed method is a promising protocol for MS analysis because of unprecedented ease, significantly enhanced sensitivity, and potentially high sample throughput.