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Dopant enriched nitrogen gas combined with sheathless CE–ESIMS for improved sensitivity and repeatability in glycopeptide analysis Guinevere Stevina Margaretha Kammeijer, Isabelle Kohler, Bas Cornelis Jansen, Paul J. Hensbergen, Oleg A Mayboroda, David Falck, and Manfred Wuhrer Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b00479 • Publication Date (Web): 27 Apr 2016 Downloaded from http://pubs.acs.org on May 1, 2016
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Analytical Chemistry
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Dopant enriched nitrogen gas combined with sheathless
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CE–ESI-MS for improved sensitivity and repeatability in
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glycopeptide analysis
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Guinevere S.M. Kammeijer1*, Isabelle Kohler1, Bas C. Jansen1, Paul J. Hensbergen1, Oleg A.
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Mayboroda1, David Falck1, Manfred Wuhrer1
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1
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*
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Proteomics
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[email protected]; Tel: +31-71-52-69384
Leiden University Medical Center, Center for Proteomics and Metabolomics, Leiden, The Netherlands
Correspondence: Guinevere S.M. Kammeijer, Leiden University Medical Center, Center for and
Metabolomics,
P.O.
Box
9600,
2300
RC
Leiden,
The
Netherlands;
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ABSTRACT
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Over the last years, numerous strategies have been proposed to enhance both ionization efficiency
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and spray stability in electrospray ionization (ESI), in particular for nanospray applications. In nano-
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liquid chromatography – mass spectrometry (nano-LC–ESI-MS), a better ESI performance has been
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observed when a coaxial gas flow is added around the ESI emitter. Moreover, enrichment of the gas
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with an organic dopant has led to an improved desolvation and ionization efficiency with an overall
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enhanced sensitivity. In this study, the use of a dopant enriched nitrogen gas (DEN-gas) combined
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with sheathless capillary electrophoresis (CE)–ESI-MS was evaluated for glycopeptide analysis. Using
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acetonitrile as a dopant, an increased sensitivity was observed compared to conventional sheathless
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CE–ESI-MS. Up to 25-fold higher sensitivities for model glycopeptides were obtained, allowing for
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limits of detection unachieved by state-of-the-art nano-LC–ESI-MS. The effect of DEN-gas on the
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repeatability and intermediate precision was also investigated. When compared to previously
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reported nano-LC–ESI-MS measurements, similar values were found for CE–ESI-MS with DEN-gas.
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The enhanced repeatability fosters the use of DEN-gas sheathless CE–ESI-MS in protein glycosylation
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analysis, where precision is essential. The use of DEN-gas opens new avenues for highly sensitive
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sheathless CE–ESI-MS approaches in glycoproteomics research, by significantly improving sensitivity
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and precision.
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Analytical Chemistry
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1. INTRODUCTION
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Electrospray ionization (ESI) - mass spectrometry (MS) hyphenated to chromatographic and
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electrophoretic separation techniques is a key technology in proteomics and glycoproteomics.
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Glycosylation is known to influence protein structure and function in multiple manners. An
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important aspect is the efficient and stable formation of gas-phase ions from solution. In nano-liquid
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chromatography (LC)–ESI-MS, the flow rates are typically kept in a range of 10-1000 nL/min and
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used in combination with a spray emitter with a narrow internal diameter, leading to the formation
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of sub-µm diameter droplets.1,2 By placing the emitter tip close to the MS entrance, it results in an
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improved sampling efficiency towards the MS, and this without the need for pneumatic assistance.
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However, the early limitations of nanospray ionization, e.g., poor spray stability and overall low
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robustness, have driven the development of more adapted emitter geometries (with respect to
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inner and outer diameter and aperture of the needle) and configurations which allow for a better
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desolvation and ion transmission.3-6
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Both droplet desolvation and sampling efficiency may be further improved by adding solvent vapors
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to the source,7 a strategy that has recently been made commercially available by Bruker Daltonics.8
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Used with a patented closed ionization source,9 the vapor-enriched gas flows coaxially around the
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ESI emitter. In combination with nano-LC–MS and by using acetonitrile (MeCN) as dopant, this
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commercial setup has shown to increase the ionization efficiency of peptides with a factor of ca. 2.6-
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fold.10,11 This setup, hereafter referred to as dopant enriched nitrogen (DEN)-gas, has also shown its
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benefits in glycopeptide analysis by providing a more than 10-fold improved sensitivity since
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glycosylated species usually show lower ionization efficiencies compared to non-glycosylated
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species.12-14
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Capillary electrophoresis (CE) is a miniaturized technique working in the nano-flow regime leading to
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high sensitivities especially when used with a sheathless interface. The commercial sheathless CE–
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ESI-MS setup (CESI technology, Sciex, Framingham, MA, US) is based on a sheathless interface
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designed by Moini where the porous end of the separation capillary which is inserted into the
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grounded needle and filled with conductive liquid, providing electrical contact via the pores.15 This
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interface has shown to display a mass-flux sensitive response at CE–ESI flow rates lower than ca. 25
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nL/min, with maximum intensity obtained at very low flow rates (
