Ionization conditions and ion formation in electrohydrodynamic mass spectrometry

• Published in: International journal of mass spectrometry and ion processes 1995-09, Vol.148 (1), p.123-144
• Main Authors: Dülcks, Th, Röllgen, F.W.
• Format: Article
• Language: English
• Subjects: Electrohydrodynamic mass spectrometry; Ion formation
• ISSN: 0168-1176; 1873-2801
• DOI: 10.1016/0168-1176(95)04250-O

The dependence of the ion signal in electrohydrodynamic mass spectrometry (EH MS) on a number of experimental parameters has been investigated with the aim of finding the conditions of optimum signal intensity and stability, also with regard to the pulsations that were found recently in the ion signals in EH MS. Investigations of the influence of the electric field strength at the capillary tip, the liquid flow rate and the conductivity (electrolyte concentration) of the sample solution largely confirmed the results of previous investigations by Evans, Jr., and co-workers and Cook and co-workers. A reduction in the surface tension by the addition of a small amount of a surfactant and an increase in the liquid temperature from 20 to 50°C both led to an increase in the signal intensity and stability and to an increase in the pulse frequencies. Both reduction in surface tension and increase in temperature did not cause significant changes in the relative ion intensities. From the experimental results a mechanism of ion formation in EH MS is derived which is similar to that of field desorption (FD) MS. In both methods the ion emission can be regarded as a desolvation process in which ions are released from the tip of liquid protrusions by successive rupture of ion-solvent bonds; the energy required for the ion release is thus divided into several steps. The main difference between EH and FD MS is due to the comparatively low viscosity of the sample substance in EH MS which causes the specific properties of the EH ion emission: the occurrence of regular, low frequency pulsations in the ion signal, the preferential release of partially solvated ions and the strong influence of surface tension on the ion signals.