title: pH Effects on Electrospray Ionization Efficiency.
abstract: Electrospray ionization efficiency is known to be affected by mobile phase composition. In this paper, a detailed study of analyte ionization efficiency dependence on mobile phase pH is presented. The pH effect was studied on 28 compounds with different chemical properties. Neither pKanor solution phase ionization degree by itself was observed to be sufficient at describing how aqueous phase pH affects the ionization efficiency of the analyte. Therefore, the analyte behavior was related to various physicochemical properties via linear discriminant analyses. Distinction between pH-dependent and pH-independent compounds was achieved using two parameters: number of potential charge centers and hydrogen bonding acceptor capacity (in the case of 80% acetonitrile) or polarity of neutral form of analyte and pKa(in the case of 20% acetonitrile). It was also observed that decreasing pH may increase ionization efficiency of a compound by more than two orders of magnitude. Graphical Abstract ᅟ.
authors.affiliation: Institute of Chemistry, Faculty of Science and Technology, University of Tartu, Ravila 14A, 50411, Tartu, Estonia. jaanus.liigand@ut.ee.
authors.forename: Jaanus
authors.identifier: 0000-0002-8814-9111
authors.initials: J
authors.lastname: Liigand
authors.affiliation: Institute of Chemistry, Faculty of Science and Technology, University of Tartu, Ravila 14A, 50411, Tartu, Estonia.
authors.forename: Asko
authors.initials: A
authors.lastname: Laaniste
authors.affiliation: Institute of Chemistry, Faculty of Science and Technology, University of Tartu, Ravila 14A, 50411, Tartu, Estonia.
authors.forename: Anneli
authors.initials: A
authors.lastname: Kruve
keywords: ESI; Electrospray; Ionization degree; Ionization efficiency; Solvent effects; pH