Is methanol a dopant under atmospheric pressure photoionization conditions?

Abstract

Using a modified atmospheric pressure photoionization (APPI) source coupled to a tunable vacuum ultraviolet source at the SOLEIL synchrotron radiation facility, we determined the appearance energy of protonated methanol monomer and dimers at different source temperatures. The experimental data indicated that protonated monomers can be formed through the direct photoionization of neutral methanol by the second emission band of a krypton discharge UV lamp at 116.49 nm (10.64 eV) explaining why methanol can be considered as a weak dopant under APPI conditions. This point is in contradiction with the previously proposed mechanism where photoionization of methanol dimer was followed by the dissociation of the protonated methanol dimer into protonated methanol monomer.

Atmospheric pressure photoionization versus electrospray for the dereplication of highly conjugated natural products using molecular networks

“…This electron or proton donor is usually a small organic molecule showing an ionization energy below 10 eV such as anisole, toluene or acetone whereas [10] the common solvents, i.e. water and acetonitrile, are not photoionized due to ionization potential at 12.6 and 12.2 eV, respectively [11]. Some families of natural products have already been studied by APPI such as pentacyclic triterpene [12], mycotoxins [13], lipids [14,15,16], chlorophyll derivatives [17], flower absolutes [18] or polyphenols [19].…”