Potentiometric detection in capillary electrophoresis with a metallic copper electrode

A copper metal electrode is used as potentiometric detector for capillary electrophoresis. The detector response is based on the complexation of copper ions at the electrode surface, which leads to a decrease of the electrode potential when the eluted analyte forms more stable copper complexes than the running buffer. A mixture of nine underivatized amino acids was separated within 7 min using basic carbonate and borate buffers as running electrolyte and detection was realised by potential measurement at a copper disk electrode in the wall-jet configuration. Calibration curves showed dynamic ranges of three orders of magnitude and detection limits of 5.9×10−6 M for threonine and 3.2×10−6 M for lysine.