Chromatographic performance of microfluidic liquid chromatography devices: Experimental evaluation of straight versus...

We prepared a series of planar titanium microfluidic (μLC) columns, each 100 mm long, with 0.15, 0.3 and 0.5 mm i.d.'s. The microfluidic columns were packed with 1.8 μm C18 sorbent and tested under isocratic and gradient conditions. The efficiency and peak capacity of these devices were monitored using a micro LC instrument with minimal extra column dispersion. Columns with serpentine channels were shown to perform worse than those with straight channels. The loss of efficiency and peak capacity was more prominent for wider i.d. columns, presumably due to on-column band broadening imparted by the so-called "race-track" effect. The loss of chromatographic performance was partially mitigated by tapering the turns (reduction in i.d. through the curved region). While good performance was obtained for 0.15 mm i.d. devices even without turn tapering, the performance of 0.3 mm i.d. columns could be brought on par with capillary LC devices by tapering down to 2/3 of the nominal channel width in the turn regions. The loss of performance was not fully compensated for in 0.5 mm devices even when tapering was employed; 30% loss in efficiency and 10% loss in peak capacity was observed. The experimental data for various devices were compared using the expected theoretical relationship between peak capacity P_c and efficiency N; (P_c-1) = N^0.5 × const. While straight μLC columns showed the expected behavior, the devices with serpentine channels did not adhere to the plot. The results suggest that the loss of efficiency due to the turns is more pronounced than the corresponding loss of peak capacity.