Carbon film based ring‐disk and split‐disk dual electrodes as detectors for microbore liquid chromatography

Abstract

The electrochemical properties of carbon film based ring-disk and split-disk electrodes in small active volume (0.24-2 pL) radial flow cells were studied in order to employ them in conjunction with microbore liquid chromatography (LC) for determining catechokdmines. 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 /Lm.On the other hand, a higher limiting current was observed with the split-disk than with a coinmercially 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 ringdisk 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.

Capillary gap flow cell as capillary-end electrochemical detector in flow-based analysis

“…4(a). In the past, the ܸ ா of alternative EC detectors have been calculated based on applying a simplified method for a known detector geometry, by multiplying electrode surface area and gap distance [18,19,22]. In this present study, ܸ ா has been measured experimentally, through varying gap distance and flow rate.…”

“…These include difficulties in miniaturisation of the system [13][14][15], frequent repolishing of the electrode [16], and low efficiency of EC conversion, typically 4-5% [17]. Additionally, there are technical issues such as a lack of experimentally determined effective cell volume (ܸ ா ) data for the different gap distance (capillary outlet-electrode) in existing EC detectors [18][19][20][21], as well as the necessity of cleaning the electrode surface during or after the experiment, and lack of EC detectors capable of being coupled with chromatographic separation platforms operating at flow rates within the nano-to millilitre per minute range [13,16,17,[19][20][21][22]. The existing mechanisms of TL-and WJ-FC in terms of layer and jet formation is reported in Hubbard et al [23], Gunasingham [13], and Patthy et al [16] respectively, which stipulate rigid construction of the EC detection FCs.…”

Recycling Systems Based on Screen-Printed Electrodes

“…Based on their diphenolic structure redox reactions at the phenolic ring can be used as sensing reactions. Several systems based on bienzymatic combinations [2,3], monoenzymatic electrode modifications [4][5][6][7][8], chemical recycling [9] or interdigitated electrodes [10] have been described.…”

Carbon fiber/epoxy composite ring–disk electrode: Fabrication, characterization and application to electrochemical detection in capillary high performance liquid chromatography

“…The limited collection efficiency is due to the fact that the ring electrode is only a thin CVD film. Ring-disk electrodes fabricated through micromachining have a higher collection efficiency (close to 0.9) because the gap is small (5 μm)[31]. …”

“…Past efforts towards making ring-disk electrodes include: alternate vapor deposition of insulating and conducting material around a disk electrode (carbon fiber, metal wire, etc.) [21, 27, 28]; aligning microelectrodes around the disk electrode as the ring electrode[29, 30]; using photolithography and dry etching[31, 32] or sputtering[33] to fabricate carbon or metal thin film ring-disk electrode. These ring-disk electrodes have been applied in certain areas, but the drawbacks are obvious: vapor deposition results in a very thin conducting layer (micrometers thick) as the ring electrode; thin film electrodes are not polishable and electrochemically less well defined compared to solid electrodes; the fabrication methods involve complicated procedures and expensive equipment (vapor deposition, micromachining, etc.).…”