An optimized capacitively coupled contactless conductivity detector for microchip electophoresis is presented. The detector consists of a pair of top bottom excitation electrodes and a pair of pickup electrodes disposed onto a very thin plastic microfluidic chip The detection cell formed by the electrodes is completely encased and shielded in a metal housing These approaches allow for the enhancement of signal coupling and extraction from the detection cell that result in an improved signal-to-noise-ratio and detection sensitivity The improved detector performance is illustrated by the electrophoretic separation of six cations (NH4+, K+, Ca2+, Na+, Mg2+, Li+) with a detection limit of approximately 0.3 mu M and the analysis of the anions (Br-, Cl-, NO2-, NO3-, SO42, F-) with a detection limit of about 0 15 mu M. These LODs are significantly improved compared with previous reports using the conventional top top electrode geometry The developed system was applied to the analysis of ions in bottled drinking water samples