An Alternative Ionization Technique for LC-MS/MS Analysis Of Perfluoroalkyl Substances (PFAS) In Environmental Samples
Polyfluoroalkyl Substances (PFAS) in the Environment
Prepared by K. Organtini, S. Oehrle, D. Stevens, K. Rosnack, J. Lewis
Waters Corporation, 34 Maple St, Milford, MA, 01757, United States
Contact Information: Kari_Organtini@waters.com; 508-482-3242
Electrospray Ionization (ESI) is widely accepted as the standard technique for LC-MS analysis of PFAS in environmental samples. A novel atmospheric ionization technique for LC-MS analysis was evaluated as an alternative technique. UniSpray Ionization (USI) allows for multimode ionization of both polar and non-polar analytes in a single injection. Ionization using UniSpray occurs upon impact of the nebulized sample onto a stainless-steel pin that is held under high voltage. This mechanism of ionization generally allows for increased ionization and sampling efficiency. UniSpray was evaluated with respect to PFAS analysis to determine if it provided enhanced ionization performance for this class of globally important compounds.
Electrospray and UniSpray techniques were compared using the same set of samples and same analysis methods using various types of water and soil samples extracts. Water sample types included surface, ground and waste waters, while sand, silt, and clay samples were evaluated as representative soil types.
UniSpray analyses produced an increased response of at least 2x or greater for a majority of the PFAS compounds evaluated, including a typical variety of legacy PFAS as well as emerging PFAS of interest. One of the emerging PFAS studied was GenX which experienced approximately a 5x increase in response using the UniSpray technique. While Electrospray ionization still performs well for PFAS analysis, the increase in response experienced with UniSpray would provide many benefits for PFAS analysis. With improved sensitivity, reaching the lowest PFAS advisory levels would be easier and would provide a more robust LOQ. Alternately, with a lower limit of detection provided by increased ionization, the sensitivity requirements for the mass spectrometer would be less stringent. A smaller injection volume could be employed, increasing instrument robustness and efficiency. Decreased sample volumes would be required and may reduce field collection requirements and furthermore reduce laboratory storage requirements.