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Sublimation has been known at least since the middle ages. This process is frequently taught in schools through use of phase diagrams. Astonishingly, such a well-known process appears to still harbor secrets. Under conditions in which compound sublimation occurs, gas-phase ions are frequently detected using mass spectrometry. This was exploited in matrix-assisted ionization in vacuum vMAI) by adding analyte to subliming compounds used as matrices. Good vMAI matrices were those that ionize the added analyte with high sensitivity, but even matrices that fail this test often produce ions of likely matrix impurities suggesting that they may be good matrices for some compound types. We also show that binary matrices may be manipulated to provide desired properties such as fast analyses and improved sensitivity. These results imply that sublimation in some cases is more complicated than just molecules leaving a surface and that understanding the physical force responsible, and how the nonvolatile compound becomes charged, could lead to improved ionization efficiency for mass spectrometry. Here we provide insights into this process and an explanation of why this unexpected phenomenon has not previously been reported. 

Unprecedented ionization processes developed into powerful methods have attributes highly desirable for MS and include high sensitivity, low cost, simplicity, ability to directly analyze biological and synthetic materials, potential for high throughput, automation, exceptional robustness, and wide applicability, especially in environments outside analytical laboratories. Initial matrix-assisted ionization (MAI) results showed different selectivity relative to ESI or MALDI providing information not readily obtained with current methodologies. Here, we demonstrate the first vacuum ionization source with multi-ionization capabilities on the same high-resolution API-mass spectrometer for a range of analytical problems with sensitivity in low fmol and detection limit in low amol ranges. The potential for achieving MS and MS/MS analysis speeds of ca. 4 seconds/sample in a simple low-cost fashion is demonstrated. 

This Perspective covers discovery and mechanistic aspects as well as initial applications of novel ioni-zation processes for use in mass spectrometry that guided us in a series of subsequent discoveries, in-strument developments, and commercialization. With all likelihood, 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 the defining turning point from which key developments grew that were at the time unimaginable, and continue to surprise us in its simplistic preeminence, and is therefore a special focus here. We, and others, have demonstrated exceptional analytical utility with-out a complete understanding of the underlying mechanism. Our current research is focused on how best to understand, improve, and use these novel ionization processes through dedicated platform and source developments which convert volatile and nonvolatile compounds from solid or liquid matrices into gas-phase ions for analysis by mass spectrometry using e.g., mass-selected fragmentation and ion mobility spectrometry to provide reproducible, 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 implementa-tion to increase coverage of complex materials through complementary strengths.