The development of a counterflow‐assisted preconcentration technique in capillary electrophoresis electrospray‐ionization mass spectrometry

Abstract

A preconcentration approach for CE-MS using counterflow-assisted electrokinetic injection was proposed. The proposed preconcentration method was based on a counterflow-compatible sheathless interface. The interface was fabricated using a capillary-assembled PDMS microdevice that allowed the application of a counterflow and provided liquid-film electrical conduction. During electrokinetic injection, a hydrodynamic counterflow was introduced into the separation capillary to retard the movement of the stacking boundary to the CE outlet. Accordingly, a long injection time was achieved without a loss of CE separation. With the use of reverse polarity mode and a dynamic polybrene-coated separation capillary (filled with a 1% formic acid solution), a counterflow-assisted electrokinetic injection of peptide samples (in a aqueous solution containing 1% ammonia and 50% methanol) for 10 min provided a sensitivity enhancement of 750-1480 and a detection limit of 20 pM for the five peptide standards. The proposed technique was applied to the analysis of low nanomolar concentrations myoglobin tryptic peptides.

Recent Studies on Online Sample Preconcentration Methods inCapillary Electrophoresis Coupled with Mass Spectrometry

“…(Step 3 and 4) The inlet vial was replaced to low pH BGE and counterflow was stopped, where peptides are separated under the supporting flow by EOF. Reproduced from ref [58] with permission. case analyzing many analytes.…”

“…Wang et al developed novel interface system for counterflow-assisted FASI as shown in Fig. 4 [58]. By fabricating a PDMS-made cross channel, they supply both sheath liquid and counter-flow to the separation capillary.…”

“…FASS-related techniques such as FASI and LVSS has also been applied to CE-MS [53][54][55][56][57][58][59][60][61].…”

Field-enhanced sample injection micelle-to-solvent stacking capillary zone electrophoresis-electrospray ionization mass spectrometry of antibiotics in seawater after solid-phase extraction

“…The first stacking implemented in CE‐ESI‐MS was transient ITP . Since 2013, stacking in CE‐ESI‐MS has been achieved by transient ITP as well as by field amplification/enhancement and dynamic pH junction . Field‐enhanced sample injection (FESI) involves electrokinetic injection of a sample prepared in low conductivity diluent .…”

CE–ESI‐MS for bottom‐up proteomics: Advances in separation, interfacing and applications

“…The interface was applied to the analyses of a five‐peptide mixture in low‐EOF (60 nL/min) and high‐EOF (210 nL/min) conditions and showed the stability and versatility of the emitter (Wang & Her, ). The same group of Wang and Her adapted their interface so a counterflow can be applied to the outlet side of the capillary and thereby accommodating counterflow electrokinetic supercharging (see sample loading Section 6) (Wang & Her, ). This interface design has only been used and reported by this group and no applications in bottom‐up proteomics have been reported to date.…”