Spreading the Electrospray Umbrella: Ionization Reagents that Extend Negative Ion ESI Coverage to Low Polarity Analytes in Complex Organic Mixtures

摘要

We have investigated ionization of complex mixtures and model compounds during (-) ESI. Various modified solvent systems were compared to optimize ionization efficiency and compositional coverage. The electrochemical processes in ESI are fundamentally important and must be considered in complex mixture analysis to maximize compositional coverage. Strong electrolytes (e.g., TMAH, TMAF, KOH) enable speciation of less acidic species that cannot be efficiently detected under conventional (-) ESI conditions. Based on the current findings, it is advantageous to reduce the concentration of electrolyte or substitute for strong non-ionic bases (super-bases) and use easily reducible cations to support the current in the circuit to obtain excess charge for (-) ESI and avoid signal suppression.