Capillary electrophoresis coupled to mass spectrometry from a polymer modified poly(dimethylsiloxane) microchip with an integrated graphite electrospray tip

Abstract

Hybrid capillary-poly(dimethysiloxane)(PDMS) microchips with integrated electrospray ionization (ESI) tips were directly fabricated by casting PDMS in a mould. The shapes of the emitter tips were drilled into the mould, which produced highly reproducible three-dimensional tips. Due to the fabrication method of the microfluidic devices, no sealing was necessary and it was possible to produce a perfect channel modified by PolyE-323, an aliphatic polyamine coating agent. A variety of different coating procedures were also evaluated for the outside of the emitter tip. Dusting graphite on a thin unpolymerised PDMS layer followed by polymerisation was proven to be the most suitable procedure. The emitter tips showed excellent electrochemical properties and durabilities. The coating of the emitter was eventually passivated, but not lost, and could be regenerated by electrochemical means. The excellent electrochemical stability was further confirmed in long term electrospray experiments, in which the emitter sprayed continuously for more than 180 h. The PolyE-323 was found suitable for systems that integrate rigid fused silica and soft PDMS technology, since it simply could be applied successfully to both materials. The spray stability was confirmed from the recording of a total ion chromatogram in which the electrospray current exhibited a relative standard deviation of 3.9% for a 30 min run. CE-ESI-MS separations of peptides were carried out within 2 min using the hybrid PDMS chip resulting in similar efficiencies as for fused silica capillaries of the same length and thus with no measurable band broadening effects, originating from the PDMS emitter.

Comparing and Combining Capillary Electrophoresis Electrospray Ionization Mass Spectrometry and Nano–Liquid Chromatography Electrospray Ionization Mass Spectrometry for the Characterization of Post-translationally Modified Histones

“…However, they have not been used frequently because of their limited robustness and lack of well-established interfaces and routine analysis protocols. The most widely used method for establishing the terminating electrical contact is coating the outer surface of the CE capillary tip with a conductive material (35)(36)(37). Unfortunately, the lifetimes of such coatings are generally very limited, as they suffer from deterioration under the influence of the high voltages applied.…”

Eletroforese capilar acoplada à espectrometria de massas (CE-MS): vinte anos de desenvolvimento

“…[39][40][41][42][43][44][45][46] Com este propósito, diferentes configurações de interfaces já foram desenvolvidas, tal como acoplamento em linha com MALDI-MS. [47][48][49] Jin et al 50 apresentaram um trabalho revolucionário construindo um sistema de reator enzimático em linha no qual a bomba seringa, tradicionalmente usada para gerar o fluxo hidrodinâmico, foi substituída pelo fluxo eletroosmótico, levando as proteínas até o reator enzimático. As enzimas foram imobilizadas em uma fase estacionária e neste sistema foi possível, em uma única etapa, promover a digestão de proteínas em 12 min com um sistema integrado de eletroforese na forma de um chip e sua caracterização em um sistema MALDI-TOF-TOF (time of flight).…”

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].…”

“…A number of CE steps and components that are used in fused-silica capillaries have been transferred and successfully tested on a microchip including preconcentration on porous silica membrane [22,23], automated derivatization [29], microreactor with immobilized proteases and other proteins [181,182], UV detector [183,184], chemiluminescence detector [34,185], multiwavelength LIF detector [186], UV LIF detector [98], wall coatings [82,85], affinity CE [129], CIEF [80], and sheathless electrospray for MS [113,114].…”