Investigation of charged droplets aspirated in the electrospray ionization process

eng: This work marks the beginning of the investigation of charged droplets within massspectrometers. It is organized into an experimental and a theoretical section. The experimental part presents the first evidence for signatures of charged droplets in mass spectra acquired with commercial mass spectrometers. In a variety of instruments, droplets and their fragments were observed in the spectra. In the SCIEX 6500Triple Quadrupole instrument, a “droplet scan mode” has to be applied to observe droplet signatures. The resulting mass spectra show a significant intensity above a certain m/z, which is attributed to the occurrence of charged droplets. In addition, in two different ion traps systems from Bruker, isolation of ions in the high mass range leads to similar observations. It is noteworthy, that the ion traps do not have to be set to a specific droplet scan routine, since the signatures appear in normal scan mode. This is important evidence for the existence of charged droplets deeply in the vacuum system of different mass spectrometers. In further experiments the variation of ion source and transfer parameters of the investigated instruments lead to alterations in the resulting mass spectra. The droplet signatures are influenced by a variety of parameters. Fully eliminating this signal, however, was not possible. The second part of this work aims to establish a workflow for employing MD simulations to further investigate the charged droplets. Specifically, the simulation framework LAMMPS was used, which proved to be promising, as different molecular systems were successfully investigated with the available force fields. The simulated droplets behave as expected from basic theory. In further simulations the energy transfer to the droplet was examined. Simulated mass spectra were produced upon analyzing the disintegration pattern of the droplets.