The Simplest Method Yet for Ultrafast Desalting of Proteins and Oligonucleotides in Native Mass Spectrometry

Native mass spectrometry can provide information on the structural context and interactions of proteoforms and other biomolecules. Despite its strengths, the incompatibility of this method with nonvolatile salts present in conventional buffers limits its integration in biophysical workflows. Common desalting approaches are time- and labor-intensive, and the volatile salts used to provide ionic strength in native mass spectrometry are not biologically relevant, raising questions about the interpretation of results if desalting requires an extended time. There is thus a need for rapid desalting methods, and while several have been previously reported, these are not always easily available. To address this gap, we present the simplest, most readily accessible method for rapid desalting to date, requiring only a negligible investment, no instrument modification, no use of consumables or chromatography, and similar sample consumption to conventional nanoelectrospray ionization. We have implemented our approach, which exploits laminar flow dynamics in a capillary, on two commonly used mass spectrometers, with example applications that included protein and DNA complexes. Samples typically spent less than 1 min in contact with ammonium acetate solution and the total analysis time was ca. 2.5 min, including a washing/conditioning step before the next injection.