Direct analysis of polyaromatic hydrocarbons in soil and aqueous samples using condensed phase membrane introduction tandem mass spectrometry with low energy liquid electron ionization

Abstract

Polyaromatic hydrocarbons (PAHs) are listed as priority pollutants by the US EPA. PAH contaminated samples often require extensive sample cleanup before analysis, with the method used dependent upon the sample matrix. We present condensed phase membrane introduction mass spectrometry with liquid electron ionization (CP-MIMS-LEI) as a sensitive and universal technique that can directly analyze both aqueous and soil samples for PAHs without the need for sample clean up or instrumental modifications for different matrices. The method uses a semi-permeable hollow fibre membrane immersion probe to transfer analytes from complex samples into a solvent acceptor phase that is directly entrained at nanoliter/min flows to an LEI interfaced mass spectrometer. The resulting aerosol is desolvated under vacuum leading to analyte vaporization and subsequent electron ionization. Electron energy and LEI vaporization capillary position were examined and optimized for PAHs. The CP-MIMS probe was directly immersed in complex aqueous matrices, demonstrating low ng/L PAH detection limits and response times of ≤1.6 minutes. For soil sample analysis, 2-propanol was found to be the optimal PAH sampling solvent. Soil samples were briefly sonicated in 2-propanol, followed by direct CP-MIMS measurement. Soil sample throughput was ca 15 samples per hour, with PAH quantitation successful at μg/kg levels. The workflow is remarkably simple, fast, green, and leads to reproducible results that enable high throughput screening of heterogeneous soil samples.