The Use of Sonotrodes for Electroanalysis: Sono-ASV Detection of Lead in Aqueous Solution

Sonotrodes were made by implanting a working electrode into the tip of an ultrasonic horn. These were investigated for the use in ultrasound assisted anodic stripping voltammetry (ASV) of Pb²⁺ and Cu²⁺ in aqueous solutions to which Hg²⁺ was added to permit the formation of lead/ copper amalgam in a plating step. Insonation not only allows this preconcentration step to take place under conditions of unusually high mass transport but also causes enrichment of the trace metals in the form of intermetallic compounds leading to sharp stripping responses. The effect of increasing insonation time on the oxidation peak sizes, shapes and positions was studied. Comparison was made with the voltammetry of Pb²⁺ and Cu²⁺ observed at platinum electrodes in the absence of Hg²⁺ where broad signals for both were seen. The nature of the deposition of mercury on platinum electrodes was studied by both voltammetry and atomic force microscopy (AFM). The growth of mercury droplets with time under 'silent' plating conditions was seen. In anodic stripping experiments using platinum sonotrodes the ratio of Hg²⁺ to Pb²⁺ in the codeposition was examined along with the total amount of charge deposited for a range of Pb²⁺ concentrations. Sharp anodic stripping responses were obtained down to a Pb²⁺ concentration level of 2 μgL^-1 making sono-ASV a potentially valuable technique for the detection of Pb²⁺ in solution. In contrast glassy carbon sonotrodes were found to be unsatisfactory since the adhesion of mercury under insonation was poor.