ELECTROCHEMICAL DETECTION OF COBALT IN HAIR FOLLOWING ON-COLUMN DERIVATIZATION WITH 1-(2-PYRIDYLAZO)-2-NAPHTHOL-6-SULFONIC ACID AND REVERSED-PHASE LIQUID-CHROMATOGRAPHY

A method for the specific determination of cobalt based on reversed-ph ase liquid chromatography with amperometric detection via on-column co mplex formation has been developed. A water-soluble chelating agent, 1 -(2-pyridylazo)-2-naphthol-6-sulphonic acid (PAN-6S), is added to the mobile phase and aqueous cobalt solutions are injected directly into t he column to form in situ the cobalt-PAN-6S chelate, which is then sep arated from other metal PAN-6S chelates and subjected to reductive amp erometric detection at a moderate potential of -0.3 V. Because the pro cedure eliminates the interference of oxygen and depresses the electro chemical reduction of the mobile phase-containing ligand PAN-6S, by vi rtue of the quasi:reversible electrode process of the cobalt-PAN-6S co mplex, a low detection limit of 0.06 ng can be readily obtained. Inter ference effects were examined for sixteen common metal species, and at a 5- to 8000-fold excess by mass no obvious interference was observed . The feasibility of the method as an approach to the specific analysi s of cobalt in a hair sample has been demonstrated.