Design, optimisation, and evaluation of a sheath flow interface for automated capillary electrophoresis‐electrospray‐mass spectrometry

Abstract

A sheath-flow capillary electrophoresis-mass spectrometry (CE-MS) system utilizing a fully integrated large-bore stainless-steel emitter electrode tapered at the end for micro-ionspray operation has been developed and evaluated. A separation capillary with an outer diameter of up to 360 microm was inserted into the electrode thus forming a void volume of less than 15 nL between the capillary end and the electrospray ionisation (ESI) tip. The sheath liquid, usually methanol-water (80:20) with 0.1% formic acid for positive ion mode or methanol for negative ion mode, was delivered at 0.5-1.0 microL/min. Unlike previously reported CE-MS interfaces, the CE-MS probe was incorporated directly onto an Applied Biosystems/MDS SCIEX orthogonal-spray Turbo "V" ion source for ease of use and automatic operation. This integration enables fast and facile coupling and replacement of the separation capillary without interrupting the ion source configuration, and the sheath liquid supply. The reusable electrospray electrode was precisely fabricated and aligned with the length of the nebulizing gas tube for improved reproducibility. Automation was achieved through software control of both CE and tandem MS (MS/MS) for unattended batch sample analysis. The system was evaluated for attomole- to low femtomole-level profiling of model peptides and protein mixtures, bisphosphates, as well as antiviral nucleosidic drugs in cellular extracts.

Determination of amino acids by capillary electrophoresis‐electrospray ionization‐mass spectrometry: An evaluation of different protein hydrolysis procedures

“…The best BGE composition was 0.8% formic acid and 20% methanol. Sheath liquid methanol content was also optimized to 60% (higher amounts of solvent resulted in current drop) [32]. Figure 1 shows a typical reconstituted base peak electropherogram for a 20 mg/L amino acid standard solution sample under the best conditions.…”

“…There are three main interfaces to couple CE to MS, namely: sheathless interface, liquid junction interface, and sheath liquid interface [28][29][30][31][32]. Sheath liquid has been the most commonly used interface owing to its high stability, versatility, and commercial availability.…”

Capillary electrophoresis‐electrospray‐mass spectrometry in peptide analysis and peptidomics

“…the electroosmotic flow, these neutral coatings are usually employed in CE-MS using a sheath flow interface, since, as already mentioned above, this interface is less dependant on the EOF. For instance, linear polyacrylamide has been used as coating for peptide analysis by CE-MS [67], as well as poly(vinyl alcohol) (PVA) [37,57,73,85] demonstrating its suitability to prevent peptides adsorption during the analysis of these molecules. In fact, Hu et al [73] showed that it was possible to identify using PVA-coated capillaries and CE-MS/ MS, common pathogen microorganisms in clinical diag- nosis by means of the selective identification of some of their specific peptides selected as biomarkers.…”

Capillary electrophoresis of proteins 2003–2005

“…Several sheathless electrosprays have been constructed for fused-silica capillary [107,110,111], glass microchips [112], and plastic microchips [113,114]. A new design of CE-MS interface was applied incorporating directly the CE-MS probe orthogonal-spray ion source [115].…”