Microfluidic nitrogen-assisted nanoelectrospray emitter: A monolithic interface for accurate mass measurements based on a single nozzle

- A monolithic chip-MS interface was developed for accurate m/z measurements.
- NANE improved LODs of RhB and reserpine by inhibiting ionization suppressions.
- Expansions of ions were regulated by three dimensional hydrodynamic focusing.
- Assisted nitrogen was employed to improve ionizations of sample and reference ions.
- OTS modification was applied in NANE to restrain the dissolution of PDMS monomers.

Nitrogen-assisted nanoelectrospray emitter (NANE) was developed to achieve accurate mass-to-charge ratio (m/z) measurements with a single monolithic nozzle. Deposition patterns of generated electrosprays from NANE confirmed their wrapped configurations. Additionally, the intensity of the sample ion and its ratio relative to a reference ion was inclined to focus on the central region of the spray; this trend further supported the existence of wrapped configurations. Further, the proposed NANE was fabricated from poly-(dimethylsiloxane) (PDMS) with octadecyltrichlorosilane modification to restrain the dissolution of PDMS monomers. Assist nitrogen flows were introduced to improve the ionization of reference ions. Moreover, the NANE could regulate the distribution of reference ions by microfluidic three dimensional hydrodynamic focusing. By regulating the distribution of reference ions, the ionization depression was reduced to some degree, and an improved sensitivity was accomplished compared with the mixing of sample and reference solutions. Achieved relative errors of m/z were between 0.2-4.5 ppm and 5.2-9.2 ppm for ten organic molecules and four biological macromolecules, respectively. Acceptable linear ranges were obtained in quantifications for rhodamine B and emamectin benzoate. Finally, the NANE was compatible with broad infusion rates (from 50 nL min−1 to 15 μL min−1) and solutions of different compositions (from 100% methanol to 100% water). Considering the comprehensive application of PDMS in microfluidics, the proposed NANE could be used as a compact and monolithic interface to achieve accurate m/z measurements.