On-Column Sample Enrichment for Capillary Electrophoresis Sheathless Electrospray Ionization Mass Spectrometry:  Evaluation for Peptide Analysis and Protein Identification

Abstract

Although several designs have been advanced for coupling sample enrichment devices to a sheathless electrospray ionization-mass spectrometry (MS) interface on a capillary electrophoresis (CE) column, most of these approaches suffer from difficulties in fabrication, and the CE separation efficiency is degraded as a result of the presence of coupling sleeves. We have developed a design that offers significant improvements in terms of ease of fabrication, durability, and maintenance of the integrity of the CE-separated analyte zones. Capillaries with different inside and outside diameters were evaluated to optimize the performance of the CE-MS system, resulting in a mass limit of detection of 500 amol for tandem MS analysis of a standard peptide using a 20-microm-i.d. capillary. The improved design incorporates an efficient method to preconcentrate a sample directly within the CE capillary followed by its electrophoretic separation and detection using a true zero dead-volume sheathless CE-MS interface. Testing of this novel CE-MS system showed its ability to characterize proteomic samples such as protein digests, in-gel-digested proteins, and hydrophobic peptides as well as to quantitate ICAT-labeled peptides.

On-line combination of monolithic immobilized pH gradient-based capillary isoelectric focusing and capillary zone electrophoresis via a partially etched porous interface for protein analysis

“…The HF etched porous interface had been used in 2D-CE system [11], on-line concentration of proteins and peptides in CE [15], the interface of CE-MS [16,17] and with electrochemical detection for isolating the electrochemical detector from the CE electric field [18]. Capillary interfaces made by above methods were easy to break from the etched section.…”

Capillary electrophoresis of proteins 2003–2005

“…If the capillary generates EOF, a sheathless interface can be used [105][106][107][108][109]. 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].…”

Recent Developments in Capillary Electrophoresis–Mass Spectrometry of Proteins and Peptides

“…A means to close the CE electrical circuit for analyte separation while simultaneously providing an electrical potential to the spray tip is necessary. The common interfaces can be divided into three categories: sheath-flow 16,[18][19][20]24,27,32,37,38,40,43,47,50,[53][54][55][56]60,66 and sheathless 15,17,25,26,[28][29][30]34,36,44,45,48,49,61 and liquid-junction interfaces. [92][93][94] In the sheath-flow design, a coaxial sheath liquid, usually a hydroorganic mixture, mixes with the capillary eluent at the outlet end of the capillary.…”

“…45 Janini et al 44 described a rugged interface that integrated the separation capillary, a porous electrical junction, and a spray tip on a single piece of fused-silica capillary. In a subsequent report, 49 they evaluated capillaries with different internal and external diameters for optimal performance.…”

“…They applied this later to quantitate low concentrations of gonadorelin and angiotensin II in a plasma. 30 Janini et al 49 assembled a miniaturized, membrane-based solid-phase extractor (mSPE) using a C18-impregnated extraction disk (Fig. 4).…”