Importance of gas-phase proton affinities in determining the electrospray ionization response for analytes and solvents

The effect of gas-phase proton transfer reactions on the mass spectral resp onse of solvents and analytes with known gas-phase proton affinities was ev aluated. Methanol, ethanol, propanol and water mixtures were employed to pr obe the effect of gas-phase proton transfer reactions on the abundance of p rotonated solvent ions. Ion-molecule reactions were carried out either in a n atmospheric pressure electrospray ionization source or in the central qua drupole of a triple-quadrupole mass spectrometer, The introduction of solve nt vapor with higher gas-phase proton affinity than the solvent being elect rosprayed caused protons to transfer to the gas-phase solvent molecules. In mixed solvents, protonated solvent clusters of the solvent with higher gas -phase proton affinity dominated the resulting mass spectra, The effect of solvent gas-phase proton affinity on analyte response was also investigated , and the analyte response was suppressed or eliminated in solvents with ga s-phase proton affinities higher than that of the analyte, Copyright (C) 20 00 John Wiley & Sons, Ltd.