High-voltage contactless conductivity-detection for lab-on-chip devices using external electrodes on the holder

The detection of ionic species in a polymeric planar electrophoresis device by contactless conductivity measurement is described. To our knowledge this is the first report of such measurements carried out with external electrodes which are part of the holder rather than the separation chip itself. The approach allows the use of bare devices as used for optical measurements, which greatly simplifies the method. The use of a sine wave of 100 kHz of a high amplitude of 500 V for cell excitation assures high sensitivity which is demonstrated with electropherograms for alkali and heavy metal ions as well as inorganic anions and carboxylates at concentrations between 10 and 50 muM. The determination of underivatized amino acids was also possible by using a buffer in the alkaline region where these species are present in anionic form. Detection limits were found to be in the order of 1-5 muM for the inorganic ions and between about 5 and 50 muM for the organic species.