Design and Implementation\nof a Desorption Electro-flow\nFocusing Sprayer on an Orbitrap Mass Spectrometer for DESI Mass Spectrometry\nImaging at High Spatial Resolution and at High Speed

Since desorption electrospray ionization mass spectrometry\n(DESI-MS)\nwas first presented in 2004, the fundamental design of the sprayer\nhas undergone relatively minor modifications. This changed in 2022\nwhen Takats and co-workers implemented the desorption electro-flow\nfocusing (DEFFI) sprayer design by modifying the sprayer from a commercial\nDESI system, leading to significantly improved spatial resolution\nand robustness compared with the traditional DESI-MSI sprayer design.\nHere, we present the design of a new DEFFI sprayer that can be built\nfrom standard fittings and connectors in combination with an aluminum\nspray head that can be machined in most mechanic workshops. The new\ndesign represents a cost-efficient approach to improved DESI-MSI on\nmass spectrometers from all vendors, including high-resolution instruments\nsuch as Orbitraps and FT-ICR. The new DEFFI sprayer is demonstrated\non a QExactive Orbitrap mass spectrometer, resulting in a massively\nimproved ion yield compared with the classic DESI sprayer. The improved\nion yield enables DESI-MSI at ion injection times down to 5 ms, allowing\nfor DESI-MSI at a potentially very high speed. More importantly, the\nDEFFI sprayer delivers a more robust and focused spray, which is easier\nto use and requires less optimization. It provides high spatial resolution\nwith limited effort compared with previous modifications of the traditional\nDESI design. Imaging of rat testis was performed at pixel sizes down\nto 12 μm, suggesting a spatial resolution of approximately 30\nμm, which may have potential for further improvement.