The ESI process is based on the conversion of liquid-phase analytes into gaseous ions. This transfer is achieved by pumping the solution through a spray capillary while applying a high voltage of approximately 3 to 4 kV. The resulting potential difference between the metal capillary and the counter electrode induces charge separation within the solution. At the tip of the capillary nozzle, a so-called Taylor cone is formed, which subsequently transforms into a jet. This jet in turn breaks up into charged droplets, each containing the analyte. The charged droplets undergo a gradual reduction in size as they travel along the electric field, primarily due to the successive evaporation of the solvent. This causes both a decrease in droplet size and an increase in the surface charge of each individual droplet, eventually reaching the Rayleigh limit. Upon reaching the limit, Coulomb repulsion induces the charged droplets to disintegrate into multiple droplets of smaller size in a phenomenon known as Coulomb explosion. This leads to the formation of numerous smaller droplets. The process repeats until gaseous analyte ions are released from the continuously diminishing droplets. Depending on the polarity of the applied voltage, either positive ions [M+H]⁺ can be generated in the ESI process by protonation or negative ions [M-H]^- by deprotonation of the analyte molecules. [1-3]

The application of ESI coupled with detection through FT-ICR-MS (Fourier transform ion cyclotron resonance mass spectrometry) represents a suitable method for characterizing the complex chemical composition of aerosol samples from diverse sources and for the qualitative analysis of shale oils.

Die Anwendung der ESI mit anschließender Detektion durch FT-ICR-MS (Fourier-Transform Ionenzyklotronresonanz Massenspektrometrie) stellt u. a. eine geeignete Methode zur Charakterisierung der komplexen chemischen Zusammensetzung von Aerosolproben aus diversen Quellen sowie zur qualitativen Analyse von Schieferölen dar.