Collision-Induced Dissociation of Ions within the Orifice−Skimmer Region of an Electrospray Mass Spectrometer

An equation was derived to describe the variation of the gas number density within the region between the orifice and the skimmer of an electrospray ionization mass spectrometer. The equation was used to develop a semi-quantitative model to predict the value of orifice voltages that lead to ion fragmentation within this region. This model made it possible to predict the types of solvent adducts observed for analytes at various orifice voltages. In addition, it is shown that a small number of high-energy collisions is equally effective for collision-induced dissociation as compared to a large number of low-energy collisions. Finally, this model is tested with different background electrolyte solutions and a different electrospray mass spectrometer. It is demonstrated that controlled fragmentation studies can be performed on single-quadrupole mass spectrometers, and the proposed model gives a reasonable description of the fragmentation process in both spectrometers.