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Since the pioneering work of Fenn et al. in the 1980s, electrospray ionization (ESI) has increasingly become the ionization technique of choice for molecular mass spectrometry (MS) in a broad range of chemical and biological applications because of its ability to create intact, multiply charged gas-phase ions and its ready coupling with MS. Highly charged droplets generated by electrospray are known to undergo asymmetric fission at the Rayleigh charge limit to form smaller droplets. The generation of gas-phase ions in ESI follows two possible mechanisms as described by Dole’s charged residue model (CRM) and Iribarne and Thomson’s ion evaporation model (IEM). Many currently available ESI–MS technologies highlighted in this article have been developed to improve ionization efficiency in ESI and ion transmission efficiency through the ESI–MS interface and to reduce bias and ion suppression in the ESI …