Figure 9 Electropherogram showing dual-electrode detection in microchip CEEC using gold microelectrodes. Detection of 100 µM tyrosine, HIAA, and catechol. (Reprinted with permission from Ref. 58.)

More recently, the activity of serum peptidases was investigated by capillary electrophoresis with electrochemical detection [60]. Increased peptidase activity in blood is characteristic of a number of disease states. In this application, leu-enkephalin was used as a model substrate. Leu-enkephalin and its metabolites were separated and detected with CEEC following on-capillary copper complexation. By incorporating copper in the run buffer, peptides were complexed directly on-capillary [61]. The copper(II) complexes could then be detected at +700 mV by oxidation to Cu(III). The method shows good selectivity for peptides over amino acids. This method was used to monitor the metabolism of leuenkephalin by enzymes present in a serum sample (Figure 10).