Sheathless coupling of microchip electrophoresis to ESI-MS utilising an integrated photo polymerised membrane for electric contacting.

In this article, we present a novel approach for the sheathless coupling of microchip electrophoresis (MCE) with electrospray mass spectrometry (ESI-MS). The key element is an ion-conductive hydrogel membrane, placed between the separation channel and an adjacent microfluidic supporting channel, contacted via platinum electrodes. This solves the persistent challenge in hyphenation of mass spectrometry to chip electrophoresis, to ensure a reliable electrical connection at the end of the electrophoresis channel without sacrificing separation performance and sensitivity. Stable electric contacting is achieved via a Y-shaped supporting channel structure, separated from the main channel by a photo polymerised, ion permeable hydrogel membrane. Thus, the potential gradient required for performing electrophoretic separations can be generated while simultaneously preventing gas formation due to electrolysis. In contrast to conventional make-up or sheathflow approaches, sample dilution is also avoided. Rapid prototyping allowed the study of different chip-based approaches, i.e. sheathless, open sheathflow and electrode support channel designs, for coupling MCE to ESI-MS. The performance was evaluated with fluorescence microscopy and mass spectrometric detection. The obtained results revealed that the detection sensitivity obtained in such Y-channel chips with integrated hydrogel membranes was superior because sample dilution or loss was prevented. Furthermore, band broadening is reduced compared to similar open structures without a membrane.