Ultrasonically-assisted cathodic stripping voltammetry at a boron-doped diamond electrode, has been developed for the detection of lead. At concentrations above 3 mM, linear sweep voltammetry was used to give the analytical signal from a cathodic strip of electrodeposited PbO 2 ; linearity was observed from 3±100 mM, with 3 mM being the lower detection limit. Square-wave voltammetry was then employed for the cathodic stripping step, to lower the detection limits of the technique while retaining linearity to the order of 10 À8 M. The procedure involves ultrasonic electrode cleaning, cathodic preconditioning and sono-anodic deposition of PbO 2 . This novel analytical tool is mercuryfree, oxygen insensitive and highly speci®c towards lead, yet still offers scope for further elemental diversity, particularly for the detection of copper and iron. The square-wave sono-cathodic stripping voltammetry technique was combined with an ultrasonically assisted acid digestion protocol to successfully determine the lead content of a contaminated sample of river sediment, offering signi®cant time saving over the currently used analytical procedure.

The suitability of ultrasound-assisted anodic stripping voltammetry (sono-ASV) for the detection of total copper content in beer using both mercury thin film and glassy carbon electrodes has been investigated. An immersion horn probe is introduced into a small thermostatted conventional three electrode cell (20 cm 3 ) opposite the working electrode: an ex situ mercury plated Nafion ® -coated mercury film electrode or a bare glassy carbon electrode. Minimal sample pre-treatment is required which consists of acidification of the beer with dilute nitric acid and out-gassing with argon. After the deposition of copper (as the metal or its amalgam) on the electrode in the presence of ultrasound, a square wave scan is employed to get the analytical signal. In the absence of ultrasound, electrode passivation by organic species and lower rates of mass transport prevent the observation of any measurable signals. In situ cavitational cleaning of the electrode by insonation maintains the electrode activity. Total copper content levels in the range of 100 to 300 mg Cu L 21 were determined by sono-ASV using both electrode substrates and showed excellent agreement with values provided by an independent method. This highlights the validity of the sono-ASV method as a useful electroanalytical technique in hostile media.

The first study of ultrasound-assisted adsorptive stripping voltammetry (AdSV) is reported. Power ultrasound emitted from a titanium horn probe placed opposite a working electrode in a conventional three electrode cell was applied during the preconcentration step of the adsorptive stripping voltammetric analysis of a vanadium-catechol complex at a mercury-plated copper electrode. Ultrasound was found to significantly improve the sensitivity of the procedure by increasing the rate at which the complex was deposited onto the mercury surface in comparison with silent conditions. The adsorption appeared to follow a Langmuir isotherm.Keywords: Ultrasound, Adsorptive stripping voltammetry, Mercury, Vanadium, Catechol The use of ultrasound coupled to electrochemical systems has been the subject of considerable fundamental and applied research over recent years [1,2]. A major advantage of its use is the extremely enhanced mass transport achieved [1,3], which has been exploited, for instance, in metal plating [4] and electrosynthesis [5,6]. Other features include activation and cleaning of the electrode surface [7], thermal effects [8] and the production of highly reactive intermediate species [9].Recent studies [10][11][12][13] have shown the advantages of using ultrasound in electroanalytical chemistry. In particular, the applicability of ultrasound to anodic stripping voltammetry has been investigated. Compton et al. [13] have studied the anodic stripping voltammetry (ASV) response of Pb 2+ and Cu 2+ using mercury films generated 'in situ' in the presence of power ultrasound emitted from an immersion horn probe placed opposite the working electrode in a conventional three electrode cell. Due to considerably enhanced mass transport the rate of deposition of both mercury and amalgam films is strongly increased compared to 'silent' conditions. Welldefined, very sharp 'stripping' responses for the oxidation process of the Pb and Cu amalgams were observed. This analytical procedure has been also applied to the analysis of Pb in wine samples [14]. With the use of 'sonotrodes', a different electrode geometry in which the working electrode is implanted into the tip of the ultrasonic horn, Compton et al. [15] 16]. Coury et al. [12] have developed a novel sonochemical stripping voltammetry method in which the preconcentration of the analyte is sonochemical rather than electrochemical. The metal particles are melted onto the electrode surface after being accelerated by microjets formed during sonication of the electrode.Adsorptive stripping voltammetry (AdSV) is a well-known electrochemical stripping technique which has been applied to the detection of metals such as Co, Ni, Mo, U and V [17,18] and organic compounds such as heme, codeine, cocaine and digoxin [17]. In this methodology, preconcentration of the metal is achieved by means of interfacial accumulation of the target as a metal complex on the electrode. This preconcentration step is crucial for AdSV analysis and its behavior will affect the selectivity an...

The effect of applying ultrasound during the preconcentration step of the adsorptive stripping voltammetry (AdSV) analysis of vanadium, nickel and riboflavin is presented. First, the sono-AdSV determination of vanadium(V) was achieved by interfacial accumulation of its catechol complex under ultrasound applied from an ultrasonic probe opposite a mercury-coated copper electrode. Ultrasound was found to increase the speed at which the complex was deposited onto the mercury surface in comparison with silent conditions. Similar analytical performances to those described in the literature were obtained for shorter preconcentration times under ultrasound. Second, the effect of ultrasound on the AdSV analysis of Ni 2+ was studied using a mercury film plated in situ on a glassy carbon electrode. Dimethylglyoxime was used as the complexing agent. The loss of mercury due to sonication is shown to decrease the sensitivity of the method. Third, the sono-AdSV analysis of an organic compound, riboflavin, was investigated. Accumulation of riboflavin was conducted both in a preplated mercury film electrode and on a glassy carbon substrate. Faster rates of adsorption were observed for riboflavin under the presence of ultrasound. In addition the AdSV analysis of riboflavin also benefits from surface activation of the glassy carbon electrode due to cleaning of its surface by the use of ultrasound. In this respect, partial removal of lumichrome, a less adsorbing species than riboflavin under these conditions and a product of riboflavin photolysis, has been observed under sonication.

Anodic stripping voltammetry experiments were carried out in aqueous lead solution using square wave voltammetry at insonated mercury thin film electrodes and compared to numerical theory developed in an earlier paper (Ball, J. C.; Compton, R. G. J. Phys. Chem. B 1998, 102, 3967). Excellent agreement was obtained under very fast mass transport conditions corresponding to the small (∼micrometer) diffusion layer thickness obtained under power ultrasound. The results provide further confirmation that the dominant contribution to the mass transport arises from diffusion layer thinning due to acoustic streaming except under extreme conditions. The choice of optimal square wave frequency under these conditions was investigated.