In-Line Dopant Generation for Atmospheric Pressure Ionization Mass Spectrometry

A concentric trace gas permeation tube that diffuses chemical reagents to a central carrier gas stream is used to drive chemical reaction pathways and influence gas-phase chemistry for a variety of atmospheric pressure ionization sources for mass spectrometry. Tunable permeation through the reservoir-jacketed polymer membrane is triggered by the heated gas moving through the tube, evaporating the dopant into a sheath dry gas or into a sample stream in room air without diluting the analyte concentration. The permeator is used to add dopants to an electrospray plume for analyte ion charge reduction and to perform hydrogen-deuterium exchange on biomolecules in different spray conditions. Dopants are also added to atmospheric pressure chemical ionization to favor the ionization of select components of diesel fuel. Atmospheric pressure photoionization is performed with the permeation tube in line with tubing transporting sample headspace to an enclosed discharge lamp. Toluene dopant from the permeator increases the proton transfer and charge exchange signal from clove oil and mothballs many times without exposing the laboratory to reagent fumes. Water permeation is also used to humidify the sample gas stream.