The application range of electrospray ionization mass spectrometry for the quantitative determination of stoichiometries and binding constants for non-covalent protein complexes is broadly discussed. The underlying fundamental question is whether or not the original molecular equilibrium can be preserved during the ionization process and be revealed by subsequent mass spectrometry analysis. Here, we take a new look at this question by discussing recent studies in droplet chemistry.This article is part of the themed issue 'Quantitative mass spectrometry'.
Keywords: accelerated reactions; desorption electrospray ionization; extractive electrospray ionization; microdroplet fusion; native mass spectrometry; thermodynamic equilibrium.
© 2016 The Author(s).