Increased electrospray ionization intensities and expanded chromatographic possibilities for emerging contaminants using mobile phases of different pH

• We developed a UHPLC–MS/MS system, and systematic approach, for emerging contaminants which expands chromatographic possibilities using mobile phases of different pH.
• In this work the habitual behaviour of low pH in environmental organic trace analysis is challenged.
• Our results compared poorly with both theory and how these topics have been handled in LC-MS/MS over the past 30 years.
• Our data strongly supports the questioning of the assumption that equilibrium concentrations of ions in solution reflect those produced during the electrospray process.
• Presence of nitrogen basic groups such as tertiary and secondary amines in a compound increased the intensity of the ESI+ signal, and was even further elevated in basic eluent.

In this work the habitual behaviour of low pH in environmental organic trace analysis is challenged by investigating the full potential of building a multi-component UHPLC-ESI–MS/MS method adapted to cover common emerging contaminants of many different polarities, minimizing the elements of compromise in the performance of the final analytical separation and detection. Contributes have been made by taking advantage of common commercially available technology in understanding the impact from solvent components and the ionization of analytes which can facilitate future development of robust, sensitive and precise UHPLC–MS/MS methods. All contaminants were evaluated and optimized without prejudices regarding historical residence in terms of chromatographic conditions and ESI mode; increasing multi-method's flexibility that can be implemented in routine analysis in response to new requests as well as to emerging contaminants yet to be discovered. Our data strongly supports the questioning of the assumption that equilibrium concentrations of ions in solution reflect those produced during the electrospray process. ESI responses of [M+H]+ and limits of detection were comparable, or often better at high pH compared to acidic eluents. Presence of nitrogen basic groups such as tertiary and secondary amines in a compound increased the intensity of the ESI+ signal, and was even further elevated in basic eluent. The proton affinity probably changes for many nitrogen-containing compounds during the ionization process, making the gas-phase processes very important in generation of these ions by ESI+. There were also an unexpected large number of compounds showing their highest response at pH 7 and weak ionic strength. A flow optimized, buffert free, neutral UHPLC–MS/MS method enhanced the sensitivity for the environmental important synthetic hormone ethinyl estradiol significantly.

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