Three-dimensional hydrodynamic focusing microfluidic emitter: a strategy to inhibit sample ion expansion in nanoelectrospray ionization

Abstract

A microfluidic emitter based on three-dimensional hydrodynamic focusing was developed to generate a wrapped charged aerosol plume, in which the distribution of the sample ion in the nanoelectrospray could be regulated. Deposition patterns of the wrapped spray from the proposed three-dimensional hydrodynamic focusing nanoelectrospray emitter (3D HFNE) were collected under different conditions to ensure the wrapped configuration. Moreover, sample ion intensities as well as their ratios to a focusing background ion were studied as a function of different displacements from the center of the wrapped electrospray to confirm the inhibition of ion expansion. Furthermore, the proposed 3D HFNE indicated improved sensitivities compared with a reported nanoelectropray emitter as well as its commercial ESI counterpart, and this demonstrated its capacity for determining samples with low concentrations and infusion rates. In addition, the proposed 3D HFNE was compatible with various sample flow compositions (from 100% methanol to 100% water) and a broad infusion rate range (from 10 nL min⁻¹ to 15 μL min⁻¹). Finally, its stability and durability were indicated to be acceptable for various determinations. Therefore, the 3D HFNE is a potential option to achieve on-line nanoelectrospray MS determinations using microfluidics with conventional mass spectrometers, considering its low cost and user-friendly properties.