High-voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis

Contactless conductivity detection was carried out on a planar electrophoresis device by capacitive coupling using an ac excitation voltage of 500 Vp-p and a frequency of 100 kHz. It was possible to carry out detection in this way through a cover plate of 1 mm thickness. Better sensitivity is obtained, however, by placing the electrodes into troughs that allow tighter coupling to the separation channel. The 3 x S/N detection limits are 0.49, 0.41, and 0.35 muM for the small inorganic ions K+, Na+, and Mg2+. The detection of heavy metals is demonstrated with the example of Mn2+, Zn2+, and Cr3+ with detection limits of 2.1, 2.8, and 6.8 muM, respectively. The universal nature of the method is further illustrated by the detection of citric and lactic acids, which are of interest in food and beverage analysis, and detection of three antinflammatory nonsteroid drugs, 4-acetamidophenol, ibuprofen, and salicylic acid, as examples of species of pharmaceutical interest.