On-chip intermediate optical and contactless conductivity detection for 2D electrophoretic separations

SYDES, DANIEL; KLER, PABLO A.; HUHN, CAROLIN

Marburg

Workshop; CE FORUM 2014; 2014

Regarding two dimensional electrophoretic separations the transfer of the analyte from the first to the second separation dimension is one of the most challenging aspects by means of minimizing band broadening, transfer timing and to ensure orthogonally of both separation dimensions.[1] In the literature several studies on coupling CE-CE, ITP-CE, ITP-ITP, CIEF-CE or MEKC-CE can be found, but mainly without intermediate detection on the interface between the first and the second separation dimension. With special emphasis to 2D heart cutting techniques the detection on the interface itself is crucial for a proper transfer of the analyte zone from the first to the second separation dimension.[2] Kler et. al. introduced a modular 2D electrophoretic separation approach using a microfluidic chip interface with on-column contactless capacitively coupled conductivity detection (C4D) and MS as final detection method.[3] Following this work we here present on-chip C4D and optical LED induced fluorescence intermediate detection for 2D electrophoretic separations: a) C4D detection was implemented as an intermediate detection technique for the simultaneous ITP-C4D/CE-MS analysis of the 20 proteinogenic amino acids in a non-aqueous separation medium using 80% DMSO. The ITP step was detected directly on the channel intersection of the microfluidic interface using the on-chip detection interface of the Csence One (CalvaSence, Aalen). This approach allowed the precise transfer of the analyte zone from the ITP to the CE-MS dimension, compared to the classical on-column C4D detection method at a certain distance from the bifurcation. b) Intermediate spatially resolved on-chip fluorescence detection was introduced using a 455 nm LED (FutureLED, Berlin) and a linear optical fiber array (artphotonics, Berlin) for guiding the fluorescence light to a PushBroom scanner (Allied Vision Technologies GmbH, Stadtroda) for spectral/spatial resolution and detection; as well as a chip holder system build in cooperation with J&M Analytik AG, Essingen. The proof of principle was shown by applying intermediate fluorescence detection for CE-LIF/CE-MS analysis of three different fluorescein derivatives in an ammonium acetate buffer at different pH values.