Capillary Electrophoresis to Mass Spectrometry Interface Using a Porous Junction

Abstract

A new capillary electrophoresis interface to electrospray ionization mass spectrometry (CE/ESI-MS) is introduced in which the electrical connection to the CE capillary outlet/ESI electrode is achieved by transfer of small ions related to the background electrolyte (BGE) through a porous section near the CE capillary outlet. In this design, only a small section of the capillary wall is made porous. The porous section is created by first thinning a small section of the capillary wall by drilling a well into it and then etching the remaining thin wall porous. This design has two advantages over previous designs (in which the whole circumference of the capillary was made porous): first, the capillary interface is more robust because only a small section of it is made porous, and therefore, no liquid junction is needed to secure the porous section. The electrical connection is achieved simply by inserting the capillary outlet containing the porous junction into the existing ESI needle and filling the needle with the BGE. Second, the time required to make the fused silica porous is reduced from approximately 1 h to a few minutes. In addition, there is no dead volume associated with the porous design, and because the actual metal/liquid contact occurs outside of the CE capillary, bubble formation due to redox reactions of water at the electrode does not affect CE/ESI-MS performance. The performance of this interface is demonstrated by the analyses of peptide and protein mixtures.

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

“…ESI is the method of choice for producing gas phase ions from solution because it is a very soft ionization method and is useful for the ionization of larger molecules or biomolecules. ESI-MS can be used for the analysis of complex mixtures [1][2][3][4][5] and is commonly used to couple separation techniques, such as high performance liquid chromatography (HPLC) [6][7][8][9], capillary electrophoresis (CE) [10][11][12][13][14][15][16][17][18][19][20][21], or microchannel electrophoresis (ME) [22][23][24][25][26][27][28][29] with MS. Many sample introduction methods, particularly those that employ separations, rely on pressure driven flow for sample introduction.…”

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].…”