Nanopore ion sources deliver single amino acid and peptide ions directly into high vacuum

Abstract We report a nanopore ion source for mass spectrometry that delivers ions directly into high vacuum from aqueous solutions. The ion source comprises a pulled quartz pipette with a sub-100 nm opening. Ions escape an electrified meniscus by ion evaporation and travel along collisionless trajectories to the ion detector. We measure mass spectra of 16 different amino acid ions, post-translationally modified variants of glutathione, and the peptide angiotensin II, showing that these analytes can be emitted as desolvated ions. The emitted current is composed of ions rather than charged droplets, and more than 90% of the current can be recovered in a distant collector. By circumventing the sample loss mechanisms inherent to conventional electrospray ionization (ESI), where charged droplets are sprayed into a background gas that scatters ions and degrades their transmission, the nanopore ion source could enable more sensitive proteomic analyses.