Membrane-free electrokinetic device integrated to electrospray-ionization mass spectrometry for the simultaneous removal of sodium dodecyl sulfate and enrichment of peptides

The removal of sodium dodecyl sulfate (SDS) in SDS-assisted proteomics with electrospray-ionization-mass-spectrometric (ESI-MS) analysis is an essential step in the analysis. Off-line state-of-the-art sample-preparation strategies can allow 100% removal of DS- and up to 100% peptide recoveries. These strategies, however, are typically laborious and require long analysis times and a complex experimental setup. Here, we developed a simple, membrane-free, electrokinetic, on-line, integrated SDS removal–ESI-MS device that was able to enhance ESI-MS signals of bradykinin and peptides from trypsin-digested bovine serum albumin (BSA) in samples that contained SDS micelles. The significant peptide-signal improvements were contributed by the complete removal of DS- and the enrichment of the peptides in the presence of an electric field. Enrichment was via micelle-to-solvent stacking, initially developed in capillary electrophoresis. Bradykinin percent recovery was 800%, and BSA peptide percent recovery was 87%. Enhancement factors in ESI-MS signals (after and before removal) for selected m/z values of peptides from the BSA digest were 535-693

Electrokinetic Removal of Dodecyl Sulfate Micelles from Digested Protein Samples Prior to Electrospray-Ionization Mass Spectrometry

In proteomics, dodecyl sulfate (DS^–) as sodium salt is commonly used in protein solubilization prior to tryptic digestion, but the presence of the DS^– hampers the electrospray ionization mass spectrometric (ESI-MS) analysis. The development of DS^– depletion techniques is therefore important especially when dealing with small samples where there could be poor sensitivity due to sample loss or dilution during sample preparation. Here, we present a simple and fast electrokinetic removal method of DS^– from small volumes of peptide and digested protein samples prior to ESI-MS. The selective removal was accomplished using an acidic extraction solution (ES) containing acetonitrile (ACN) inside a fused-silica capillary that was dipped into the sample. The use of acidic ES suppressed the electroosmotic flow; allowing the electrokinetic movement of DS^– monomers and micelles into the capillary. The high amount of ACN present at the tip of the capillary served to collapse the micelles migrating into the capillary, thereby releasing the peptides that were bound to these micelles, facilitating peptide retention in the sample and efficient DS^– removal. Increased % MS signal intensity (SI) restoration of the peptide was observed, while DS^– removal was unaffected when the amount of ACN in the ES was increased. This is because of the micelle to solvent stacking mechanism (effective electrophoretic mobility reversal) working at high concentration of ACN for the improved recovery of the peptides. % MS SI restoration for the Z-Gly-Gly-Val and bradykinin peptides were 75–83% while % MS SI reduction of DS^– was up to 99% under optimal conditions, that is, 40% ACN in the ES. Higher % peptide recoveries from digested protein samples were obtained using the proposed method compared to the conventional cold acetone precipitation method

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2012-2014)

One of the most cited limitations of capillary (and microchip) electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of on-line/in-line concentration methods, covering the period July 2012-July 2014. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to ITP, dynamic pH junction, and sweeping. Attention is also given to on-line or in-line extraction methods that have been used for electrophoresis