1000-Fold Preconcentration of Per- and Polyfluorinated Alkyl Substances within 10 Minutes via Electrochemical Aerosol Formation.

We present a simple and efficient method for preconcentrating per- and polyfluorinated alkyl substances (PFAS) in water. Our method was inspired by the sea-spray aerosol enrichment in nature. Gas bubbles in the ocean serve to scavenge surface active material, carrying it to the air-ocean interface, where the bubbles burst and form a sea-spray aerosol. These aerosol particles are enriched in surface-active organic compounds such as free fatty acids and anionic surfactants. In our method, we in situ generate H2 microbubbles by electrochemical water reduction using a porous Ni foam electrode. These H2 bubbles pick up PFAS as they rise through the water column that contains low concentration PFAS. When these bubbles reach the water surface, they burst and produce aerosol droplets that are enriched in PFAS. Using this method, we demonstrated ∼1000-fold preconcentration for ten common PFAS in the concentration range from 1 pM to 1 nM (or ∼0.5 ng/L to 500 ng/L) in 10 min. We also developed a diffusion-limited adsorption model that is in quantitative agreement with the experimental data. In addition, we demonstrated using this method to preconcentrate PFAS in tap water, indicating its potential use for quantitative analysis of PFAS in real-world water samples.

New Processes for Ionizing Nonvolatile Compounds in Mass Spectrometry: The Road of Discovery to Current State-of-the-Art.

This Perspective covers discovery and mechanistic aspects as well as initial applications of novel ionization processes for use in mass spectrometry that guided us in a series of subsequent discoveries, instrument developments, and commercialization. Vacuum matrix-assisted ionization on an intermediate pressure matrix-assisted laser desorption/ionization source without the use of a laser, high voltages, or any other added energy was simply unbelievable, at first. Individually and as a whole, the various discoveries and inventions started to paint, inter alia, an exciting new picture and outlook in mass spectrometry from which key developments grew that were at the time unimaginable, and continue to surprise us in its simplistic preeminence. We, and others, have demonstrated exceptional analytical utility. Our current research is focused on how best to understand, improve, and use these novel ionization processes through dedicated platforms and source developments. These ionization processes convert volatile and nonvolatile compounds from solid or liquid matrixes into gas-phase ions for analysis by mass spectrometry using, e.g., mass-selected fragmentation and ion mobility spectrometry to provide accurate, and sometimes improved, mass and drift time resolution. The combination of research and discoveries demonstrated multiple advantages of the new ionization processes and established the basis of the successes that lead to the Biemann Medal and this Perspective. How the new ionization processes relate to traditional ionization is also presented, as well as how these technologies can be utilized in tandem through instrument modification and implementation to increase coverage of complex materials through complementary strengths.

Fundamental Studies of New Ionization Technologies and Insights from IMS-MS.

Exceptional ion mobility spectrometry mass spectrometry (IMS-MS) developments by von Helden, Jarrold, and Clemmer provided technology that gives a view of chemical/biological compositions previously not achievable. The ionization method of choice used with IMS-MS has been electrospray ionization (ESI). In this special issue contribution, we focus on fundamentals of heretofore unprecedented means for transferring volatile and nonvolatile compounds into gas-phase ions singly and multiply charged. These newer ionization processes frequently lead to different selectivity relative to ESI and, together with IMS-MS, may provide a more comprehensive view of chemical compositions directly from their original environment such as surfaces, e.g., tissue. Similarities of results using solvent- and matrix-assisted ionization are highlighted, as are differences between ESI and the inlet ionization methods, especially with mixtures such as bacterial extracts. Selectivity using different matrices is discussed, as are results which add to our fundamental knowledge of inlet ionization as well as pose additional avenues for inquiry. IMS-MS provides an opportunity for comparison studies relative to ESI and will prove valuable using the new ionization technologies for direct analyses. Our hypothesis is that some ESI-IMS-MS applications will be replaced by the new ionization processes and by understanding mechanistic aspects to aid enhanced source and method developments this will be hastened.