Simple Atmospheric Hydrogen/Deuterium Exchange Method for Enumeration of Labile Hydrogens by Electrospray Ionization Mass Spectrometry

A simple method for hydrogen/deuterium exchange in a standard electrospray (ESI) ionization source is presented. In this method, a D2O droplet is placed between the ESI needle and the entrance of the mass spectrometer and thus saturation of the atmosphere with deuterated vapor, in the ESI region is achieved. It was shown that full exchange of up to 23 labile acidic hydrogens with a minimal back exchange with the surrounding atmospheric water can be performed by this method.