C-Term Reduction in 3 μm Open-Tubular High-Aspect-Ratio Channels in AC-EOF Vortex Chromatography Operation.

The performance of liquid chromatography operation in open-tubular channels, the ideal chromatographic column format, is limited by slow mass transport between the mobile and stationary phase. We recently introduced a lateral mixing methodology ("vortex chromatography") to reduce Taylor-Aris dispersion by employing (small) AC-EOF (alternating current electroosmotic flow) fields oriented perpendicular to the conventionally applied, axially oriented pressure gradient, resulting in the reduction of the C-term by a factor of 3, studied in 40 × 20 μm 2 (aspect ratio (AR) = 2) channels under unretained conditions. In the present contribution, a further increased performance gain for channel dimensions relevant for chromatographic applications is demonstrated. The impact of the applied voltage and salt concentration is studied for 3 × 20 and 5 × 20 μm 2 channels in ARs of up to 6.7, revealing a C-term reduction potential of a factor of up to 5 for large molecules (dextran) under unretained conditions. The decrease in κ aris in a 5 μm channel (reduction of 80%) was larger than the decrease in a 3 μm channel (reduction of 44%).