Enhanced instrumentation and preparative separation performance of orthogonal high-pressure electrochromatography

Orthogonal High-Pressure Electrochromatography (OHPEC) combines liquid chromatography with a perpendicularly applied electric field in a bulk-packed planar column, representing a significant advance over systems based on chromatography plates. Here, we report an upgraded OHPEC planar column that addresses the key limitations of earlier configurations and provides the first experimental demonstration of continuous separation in this technique. The OHPEC system can operate in either periodic or continuous mode, allowing the operation mode to be selected according to the chromatographic retention and electrophoretic mobility of the target compounds. The redesigned electrode chambers, equipped with active flushing and degassing, are integrated into a fully automated system that reduces flushing time and solvent consumption by 50% while enhancing stability against Joule heating and water electrolysis. During operation at 1.0 kV for 100 min, the outlet temperature increased by <5%, and the pH deviation remained within one unit, compared with over 20% temperature rise and a four-unit pH shift in the earlier design. The improved packing procedure reduced the plate height from about ten to three particle diameters, corresponding to an expected reduction in column-generated peak width of about 40%. Sample introduction studies showed that the multiple-injection system, a piston-based alternative to fixed-volume loops, produced 10-20% narrower peaks at higher injection volumes. Together, these modifications substantially increased the practical throughput of the OHPEC separation system. During preparative separation of the test mixture at 2.5 kV, the system exhibited good reproducibility, with %RSD values below 1.6 for retention time, 3.6 for peak width, and 5.2 for peak area. Theoretical modelling based on analytical-scale data can provide a useful starting point for estimating operating parameters for preparative separations, although experimental verification remains necessary.