Radial Flow Microring Electrode:  Development and Characterization

Abstract

The radial flow microring electrode (RFMRE), a new hydrodynamic ultramicroelectrode, is described. In the RFMRE, solution flows from a capillary nozzle, which is positioned very close to a planar substrate using micropositioners. The RFMRE can be operated in one of two configurations: either (a) with the ring electrode on the capillary or (b) with the ring electrode positioned in the plane of the substrate directly underneath the capillary. In both arrangements, as fluid leaves the capillary, it is forced into the nozzle/substrate gap and flows radially past the ring electrode. Under these conditions, the RFMRE is effectively analogous to a microband channel electrode. The RFMRE is shown to be characterized by well-defined, variable, and high mass-transfer rates under steady-state voltammetric conditions. Mass-transfer coefficients in excess of 2 cm s -1 have been readily achieved with the RFMRE operating at relatively low volume flow rates (1.67 × 10 -2 cm 3 s -1 ). The device thus has considerable promise for electroanalysis and the study of fast electrode kinetics.The ability to characterize both heterogeneous electrode reactions and coupled homogeneous solution reactions with increasingly faster kinetics is a major challenge in electrochemical research. 1 The attainment of this goal requires the availability and development of techniques that are able to deliver the necessary high mass-transfer rates to compete with the reaction kinetics, under defined and controllable conditions. Hydrodynamic techniques, 2,3 where the electrode moves with respect to the solution, as with rotating (or vibrating) disks, 3 rings, 4 wires, 5 and photoelectrodes, 6,7 or where solution is forced past a stationary electrode, as exemplified by conical, 8 band, 9 and S0003-2700(98)00166-8 CCC: $15.00

Electroanalytical Flow Measurements–Recent Advances

“…With conventional electrode systems under laminar flow conditions the maximum mass-transfer rates up to ca. 0.05 cm/s were reached, while with a radial flow microring electrode mass transfer coefficients in excess of 2 cm/s were reported [42]. Such systems are excellent tools for measurement of fast reaction rates [43].…”

“…While in conventional-sized voltammetric systems with laminar flow a maximum mass-transfer rates up to about 0.05 cm/s is reached, for instance, in radial flow micro ring electrode (66 mm ring diameter) mass-transfer rates in excess of 2 cm/s can be achieved, which provides a significant enhancement of detection sensitivity [42]. A set of disk microelectrodes of radii ranging from 5 to 25 mm was used in a wall-jet cell with amperometric detection for indirect determination of nitrite in saliva based on its reaction with iodide [122].…”

Scanning Electrochemical Microscopic Study of Hydrogen Oxidation and Evolution at Electrochemically Deposited Pt Nanoparticulate Electrode Incorporated in Polyaniline

“…Thus the key issue of achieving an effective mass transfer rate, (∼D/d) higher than heterogeneous kinetics, could be greatly affected due to the tip size. This problem could be minimized by using the impinging jet 29,30 since such hydrodynamic approaches produce significantly high mass transfer rates, studies in this regard are now underway in our group. A high rate constant value for H2 oxidation at 0.2 -0.5 µm Pt particles was also noticed earlier.…”

A Glass Capillary Ultramicroelectrode with an Electrokinetic Sampling Ability

“…9 Taking an advantage of the very small tip size, pulled glass capillaries have been employed as microholders for constructing electrochemical microsensors, such as carbon fiber microelectrodes, 10,11 bilayer lipid membrane microsensors [12][13][14] and oxygen microsensors, 15 and also in achieving enhanced and variable mass-transfer rates at a hydrodynamic ultramicroelectrode. 16 The use of glass capillaries with a conical or cylindrical tip (1.5 -2 µm) as a diffusional microburet for microtitration [17][18][19] and quantitative reagent delivery for fine chemical manipulations 20,21 has also been reported. Recently, Wei et al have reported that pulled quartz tubes with orifice radii of ~20 nm form a diffuse electrical double layer within the tip, leading to charge-selective ion movement across the tip.…”