18-Crown-6 spiking in direct infusion ESI-MS analysis of complex mixtures: “One ion per analyte” relationship facilitating ion assignments and eliminating isobaric interferences

•Regular formic acid spiking does form ionic species with high sodium and potassium cationic content.•Use of 18-crown-6 ether capture sodium and potassium eliminating them from the solution.•Trifluoracetic acid protonates the neutral molecules.

Spiking with 18-crown-6/trifluoracetic acid is shown to sequester metal cations thus eliminating unwanted [TAG+Na]+ and [TAG+K]+ ions whereas favoring analyte detection as sole [TAG+H]+ ions in the ESI(+)-MS analysis of methanolic solutions of soybean oil. This sequestering eliminates ion splitting and its resulting isobaric interferences, thus increasing spectra quality greatly facilitates analyte identification. This “one ion per analyte relationship” is highly beneficial for direct infusion analysis of complex mixtures by ESI-MS.