Ultrasound Assistance to Electroanalytical Techniques

The current status of electroanalytical techniques is reflected in its decreased instrumental development relative to optical techniques and mass spectrometry. Some authors have pointed out that, despite the extensive work conducted on model systems, electroanalytical techniques have not yet reached full development [125]. 

The use of electroanalytical techniques in routine analyses, particularly those involving samples with organic constituents, has been traditionally curtailed by two main shortcomings, namely (a) fouling and passivation of the electrodes by species depositing on their surface, which affects all electroanalytical techniques and (b) slow mass transport to the electrode and slow kinetics of electron transfer, which affect the sensitivity of redox-based techniques. 

Ultrasound assistance can be provided before and (or) during analysis. In those techniques which do not involve any electron exchange at the solution-electrode interface, US is normally applied prior to analysis in order to activate the electrode surface and hence in the absence of sample in electron-exchange processes, US can be applied as a pretreatment, but also during analysis. In the latter case, US can be applied during the measurement step and, in stripping techniques, during deposition of the analyte of interest on the electrode, either electrochemically or by physisorption. 

The assistance of US to electroanalytical techniques during analysis is known as sonoelectroanalysis. This should also include the use of low-frequency sound (below 20 kHz), which has been found to significantly increase mass transport and the limiting current (and sensitivity as a result) [127-130]. 

This section discusses the potential of sonoelectroanalysis, expansion of which is currently at a standstill owing to the few groups working on it. With few exceptions involving baths, probes are the ultrasonic sources used to assist electroanalytical processes with US. Some authors have pointed that the low, spatially variable distribution of ultrasonic intensity provided by baths is a major hindrance for using these devices with electroanalytical techniques [131]. Therefore, most of the examples described in this section involve the use of probes as US sources. 

---

Experimental devices used for ultrasound assistance to electroanalytical techniques... 

---