Characterization of a miniaturized liquid bridge for nL sample infusion: a comparative study of sample flush-out behavior using flow simulations and direct ESI-MS analysis |
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Authors: | Volker Neu Pablo Dörig Christof Fattinger Stephan Müller Renato Zenobi |
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Affiliation: | 1.Department of Chemistry and Applied Biosciences,ETH Zurich,Zurich,Switzerland;2.Laboratory of Biosensors and Bioelectronics,Institute of Biomedical Engineering, ETH Zurich,Zurich,Switzerland;3.F. Hoffmann-La Roche AG, pRED, Pharma Research & Early Development, Discovery Technologies,Basel,Switzerland;4.Competence Center Analytics, BASF SE,Ludwigshafen,Germany;5.Cytosurge AG,Glattbrugg,Switzerland |
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Abstract: | In this work we shed light on the microfluidics of a miniaturized liquid bridge that forms the central part of a so-called “capillary gap sampler,” a novel device for rapid and seamless injection of nanoliter sample volumes into an electrospray ionization mass spectrometer (ESI-MS). Parameters relevant for sample flush-out at the liquid bridge and in the spray capillary were identified by systematic variation of the capillary dimensions, the linear buffer flow rate (2.1–34 mm/s) and molecular weight of the analytes (0.5–30 kDa). We found that a reduction in capillary wall thickness by a factor of 1.6 significantly influences analyte peak shapes, leads to an inversion of the relationship between peak width and analyte molecular weight, and allows a fivefold decrease in peak width for large molecules down to 5 s. The results could be verified and explained by simulations, in which the presence of diffusion-controlled “dead zones” at the liquid bridge and dispersion in the spray tip that depend on analyte molecular weight were identified as key factors relevant for the sample flush-out process. The merging of simulations and experimental data gives useful hints toward the re-design of a spray tip as built-in ESI-MS interface for an optimized gap sampler performance. |
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