Improving MCE with electrochemical detection using a bubble cell and sample stacking techniques

Two efforts to improve the sensitivity and limits of detection for MCE with electrochemical detection are presented here. One is the implementation of a capillary expansion (bubble cell) at the detection zone to increase the exposed working electrode surface area. Bubble cell widths were varied from 1 x to 10 x the separation channel width (50 mu m) to investigate the effects of electrode surface area on detection sensitivity, LOD, and separation efficiency. Improved detection sensitivity and decreased detection limits were obtained with increased bubble cell width, and LODs of dopamine and catechol detected in a 5 x bubble cell were 25 and 50 nM, respectively. Meanwhile, fluorescent imaging results demonstrated similar to 8 and similar to 12% loss in separation efficiency in 4 x and 5 x bubble cell, respectively. Another effort at reducing the LOD involves using field amplified sample injection for gated injection and field amplified sample stacking for hydrodynamic injection. Stacking effects are shown for both methods using amperometric detection and pulsed amperometric detection. The LODs of dopamine in a 4 x bubble cell were 8 and 20 nM using field amplified sample injection and field amplified sample stacking, respectively. However, improved LODs were not obtained for anionic analytes using either stacking technique.