Hydrodynamic Modulation Voltammetry with an Oscillating Microjet Electrode

Abstract

A new method of hydrodynamic modulation voltammetry (HMV) is introduced, based on the microjet electrode (MJE) with an oscillating nozzle position. In MJE-HMV a jet of solution is fired at high velocities from a nozzle (with a typical diameter in the range 25−50 μm) onto the surface of a disk ultramicroelectrode (UME). The mass transport rate to the electrode is modulated by oscillating the lateral position of the jet between two different coordinates: one where the jet impinges directly on the electrode surface and the other where the flowing stream (largely) misses the electrode. The resulting modulated (transport-limited) current in phase with the moving jet is quantitative and discriminates effectively against background processes. Studies of iridium (III) hexachloride (IrCl6 3-) oxidation at a Pt MJE serve to demonstrate the general capabilities of the technique. For this system, detection limits are estimated to be ∼5 × 10-9 mol dm-3. In its present form, modulation frequencies of as much as 20 Hz can be successfully employed without serious attenuation of the current signal, and there is scope for further improvement through the use of smaller nozzles and electrodes and piezoelectric positioners with improved frequency responses.

Delayed voltammetric with respect to amperometric electrochemical detection of concentration changes in microchannels

“…This time was previously used to quantify the ability of the diffusion processes observed at the electrode to respond to alterations in mass transport at one edge of the diffusion layer after variations of the flow velocity. 41,42 By analogy with these works, the reaction rate, controlled by the potential ramps during CV, will also alter the mass transport defining the diffusion layer, and the time required for the diffusion layer to adapt to these new conditions is expected to be described by τ D . This characteristic time can be related to δ D :…”

Exploring the applications of a pulsating jet hydrodynamic modulated voltammetric (HMV) system – Electrochemistry of nanostructured Pt electrodes and trace analysis

“…Here we show how hydrodynamic modulated voltammetry [9,10] (HMV) may be used to overcome some of these difficulties. This is a direct result of HMV offering the advantage of discrimination between solution phase Faradaic processes and non-Faradaic or surface bound Faradaic processes [11][12][13][14]. In particular we use HMV to investigate the important electrochemical reduction of molecular oxygen at a nanostructured [15] Pt electrode.…”

“…In the first, flow to the electrode can be modulated in a periodic manner. This may involve modulation of the rotation rate of a rotating disc electrode or alteration of the flow to an electrode by 'chopping' or oscillating the flow in a suitable manner [13,14,21,22]. In the second, the modulation of the signal required is generated by the mechanical oscillation of an electrode [11,12,23].…”

An HMV mapping study of a pulsating jet system

“…Other examples of these systems involve, pulsed rotation [12][13][14][15], vibrating electrode techniques [16,17], ultrasonic cavitation [18,19] or, more recently, vibrating or chopped capillary flow systems based around a novel scanning electrochemical microscopy (SECM) technique [20][21][22]. In all of these cases the detection limits proposed have been impressive, generally below 0.5 µmol dm -3 .…”