Carbon Film Based Ring-Disk and Split-Disk Dual Electrodes as Detectors for Microbore Liquid Chromatography

The electrochemical properties of carbon film based ring-disk and split-disk electrodes in small active volume (0.24-2 μL) radial flow cells were studied in order to employ them in conjunction with microbore liquid chromatography (LC) for determining catecholamines. The high conversion of dopamine (DA) at the disk of a ring-disk electrode makes the DA limiting current lower than the theoretical value at a low flow rate. The collection efficiency (CE) increases with decreasing flow rate and cell thickness, which is different from previously reported results. A high CE of 0.96 was achieved because of the narrow gap of 5 μm. On the other hand, a higher limiting current was observed with the split-disk than with a commercially available dual-disk electrode because of its efficient geometry for analyte collection. The cross talk of the DA after reacting at one of the electrode is only 2%. The ring-disk and split-disk electrodes were suitable as series and parallel electrochemical detectors for small bore LC. A detection limit of 103 fg was obtained for DA at the disk of the ring-disk because of the high signal in the thin-layer radial flow cell and the low noise level of the carbon film. In contrast, very slight interference was observed from neighboring electrodes when determining catecholamines at the split-disk.