Amplifying ion signal levels for MS/MS and MSn applications in native MS experiments in negative ion mode using cVSSI techniques

Capillary vibrating sharp-edge spray ionization (cVSSI) has been investigated for its utility in tandem mass spectrometry (MS) and multistage tandem MS (MSn) experiments for native MS analyses in negative ion mode. Compared with capillary electrosprayionization (cESI) and heated electrospray ionization, cVSSI provided significant increases (up to >1000 fold) in ion signal levels. Signal-to-noise ratio (S/N) show a reduction in difference where cVSSI provides an increase of up to 7 fold. Performing MS3 experiments on all biomolecules examined here showed that more fragment ions could be identified from the cVSSI experiments. Additionally, the ion intensity levels of fragment ions observed with all ionization sources exceeds the S/N advantage of the precursor ions. Tracking MS/MS product ions as a function of analyte concentration reveals an ~10 fold sensitivity advantage for the cVSSI approach when compared with the other ionization sources. Taken together, the results highlight the importance of the total ion signal advantage provided by cVSSI (as opposed to S/N) and are discussed in light of ion utilization considerations. Finally, separate experiments demonstrate that the ion signal level advantages hold even for samples for which small amounts of organic solvent are used to improve ionization.