Calibration of the internal energy distribution of ions produced by electrospray

The internal energy deposited in the ions in the source of a mass spectrometer governs their fragmentation and therefore the content of the spectra. When the ionization conditions are well defined and reproducible, e.g. in electron impact, the elaboration of databases benefits the use of the method. In electrospray, however, the source conditions are not strictly defined. The elaboration of spectra databases therefore requires a calibration of the internal energy of the ions that is valid for all types of spectrometers. A method for the calibration of the internal energy of ions in electrospray is presented, developed using the fragmentation reactions of a set of probe ions (benzylpyridinium salts) under various conditions (the voltage on the sampling cone, the nature of the collision gas, the composition of the mobile phase). The influence of the experimental conditions on the internal energy of the ions permits the calibration of individual working conditions. © 1998 John Wiley & Sons, Ltd.