Survival yield comparison between ESI and SAII: Mechanistic implications

• None of the solution based ionization methods of ESI, ESII, and SAII are sufficiently energetic to cause fragmentation of any of the thermometer ions studied.
• Methods that use voltage to produce charged droplets such as ESI and ESII produce more fragmentation of thermometer ions than voltage-free SAII under nearly identical conditions.
• The apparent softness of SAII appears to be related to analyte ions being protected from temperature and voltage effects within solvent droplets for longer time.
• Thermometer ions produced from solid matrix particles fragment more under the same conditions than these ions produced by ESI.

The survival yield (SY) method is commonly used in mass spectrometry to determine the energy deposited into ions by an ionization process. SY is the fraction of intact molecular ions that remain after fragmentation. In this study, we compared the fragmentation of three different thermometer ions as a function of various inlet voltages on an Orbitrap Exactive mass spectrometer using solvent assisted ionization inlet (SAII), electrospray ionization (ESI), and electrospray ionization inlet (ESII). The data shows that under the same inlet conditions SAII, which does not use a voltage, produces less fragmentation than either ESI or ESII, methods that use a voltage to initiate ionization. However, in the Orbitrap Exactive, fragmentation is more significantly related to the energy imparted to the ions during transition from the ionization region to the mass analyzer than to the ionization process. By minimizing the energy acquired during ion transfer to the mass analyzer, fragmentation is significantly decreased for the thermometer ions using any of the ionization methods. These results demonstrate that the ionization processes are insufficiently energetic to provide the necessary energy of activation for fragmentation of the thermometer ions studied here. By using voltages in the intermediate pressure region after the inlet tube to add energy to the ions during the transfer to the mass analyzer, differences in the SY are observed between ESI and SAII. The mechanistic implications relative to SAII and ESII are discussed along with comparisons with matrix assisted ionization inlet using the solid matrix 3-nitrobenzonitrile.

Figure optionsDownload high-quality image (120 K)Download as PowerPoint slide