Characterisation of a simple electrochemical detector for high-performance liquid chromatography and flow-injection analysis based on carbon microcylinder electrodes Original Research Article

A simple thin channel flow cell, modified to incorporate carbon microcylinder indicator electrodes, was tested as an amperometric detector in high-performance liquid chromatography (HPLC) and flow-injection analysis (FIA). The hydrodynamics of the cell were studied by means of steady state electrochemical experiments at varied flow rates. The signal dependence on flow rate has proven that for 30 μm diameter microcylinder electrodes, convective diffusion prevails and no radial diffusion effects are observed. Nevertheless, mass transfer rates are enhanced for microcylinders placed perpendicular to the analyte flow. In HPLC and FIA experiments with typical electroactive analytes, the microcylinder-based detector gave good quality responses and, when operated at potentials near the mass transfer control region, exhibited an improved sensitivity and signal-to-noise (S/N) ratio, resulting in lower detection limits (less than 10 ppb) than a macroelectrode indicator. This is in complete agreement with simple considerations for the analyte signal and background current at thin electrodes with their smaller dimension parallel to the flow velocity in a channel cell.