A simplified electrospray ionization source based on electrostatic field induction is introduced in this paper. The electrostatic field induced spray ionization, termed EFISI, is easily performed using a needle electrode and a capillary, and it does not require heat, gas, a syringe pump or any other equipment. A high voltage is applied to a needle electrode which does not contact the sample. The capillary is used as a sample spray emitter without any electrical contact or tip modification. As only a 1 μL sample droplet is needed for analysis with no or little pretreatment, the EFISI source is particularly suitable for the mass spectrometric analysis of microlitre volume samples. The change of charge distribution in the droplet solution, by the induction of an external electrostatic field from the needle electrode, is proposed to be the main cause of ion formation. We demonstrate its feasibility for the characterization of a wide range of organic compounds and biomolecules in pure solutions or complex matrices. The influence of sample capillary length and droplet solvent composition on the ionization process are also discussed.
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