High-pressure nanoESI of highly conductive volatile and non-volatile buffer solutions from a large Taylor cone: Effect of spray current on charge state distribution

Direct ESI-MS of proteins in nonvolatile buffer requires the generation very fine initial droplets to resolve peak for meaningful analysis. This is usually achieved using nanoESI capillary with an inner diameter ∼1 μm or smaller. Recently we reported “true nanoelectrospray” from a micropipette tip large under super-atmospheric pressure condition (J. Am. Soc. Mass Spectrom. 2022, 33, 491–498). The flow rate nL/min regime can be reproducibly adjusted high voltage spray current as indicator rate. Here two further works are done on same ion source. First, validation current-flow relationship has been extended 0.5 MPa, and achievable minimum found reduce source pressure. Second, applied study effect charge state distribution nanoflow peptides volatile (formic acid ammonium acetate) (phosphate saline (PBS) 1 M Tris-HCl) buffers. For buffers, clean mass spectra only obtained at low nL/min. average tested primarily determined by type buffer. acidic solutions, shifts higher value lower non-denaturing number remained relatively constant but variation appeared analyte dependent.