Voltammetry, microwave-activated

Microwave-activated voltammetry has been applied to the ferrocyanide/ferricyanide redox couple145, reduction of Ru(NH3)g 146, enhanced Pb02 electro-deposition, stripping and electrocatalysis147 and electrodehalogenation in non-aqueous media148. 

Manivannan et al. used diamond electrodes to detect Pb(II) in water samples (pH = 1) by differential pulse voltammetry, measuring concentrations down to 4 nM (0.8 ppb) [57]. The preconcentration step was rather long at -1.0 V vs. SCE for 15 minutes. Prado et al. reported on the detection of Pb(II) and Cu(II) at diamond electrodes using anodic stripping voltammetry [156]. The Pb(II) was detected by both anodic- (Pb metal) and cathodic-stripping voltammetry. Pb(II) was detected in a river-water sediment sample (pH = 1) and was quantified using a standard addition method. The metal content in the sediment was found to be - 200 mg/kg by both anodic- and cathodic-stripping voltammetry. The electrode response was improved after microwave activation (e.g., thermal treatment), with a limit of detection of 21 ppb for a 20-second preconcentration time. 

Fig. 4.3 Arrangement for microwave-activated voltammetry. From [15], with permission...

Stripping voltammetry experiments at a boron-doped diamond electrode with 2 mM Pb2+ in 0.1 M HNO3 were carried out in order to study the effect of microwave radiation on this process. Microwave activation has a considerable effect on the square-wave stripping response, with signal to noise improvements of more than one order of magnitude. 

The limit of detection by square-wave voltammetry after a 20-s deposition time was found to be 0.1 mM and 1.0 mM with and without microwave activation, respectively. The Pb content in a water sediment sample detected by anodic stripping voltammetry at boron doped diamond electrodes is shown to be in good agreement with two other independent analytical procedures based on ICP mass spectroscopy and on sono-cathodic stripping voltammetry. 

The apphed pretreatment techniques were digestion with a combination of acids in the pressurized or atmospheric mode, programmed dry ashing, microwave digestion and irradiation with thermal neutrons. The analytical methods of final determination, at least four different for each element, covered all modern plasma techniques, various AAS modes, voltammetry, instrumental and radiochemical neutron activation analysis and isotope dilution MS. Each participating laboratory was requested to make a minimum of five independent rephcate determinations of each element on at least two different bottles on different days. Moreover, a series of different steps was undertaken in order to ensure that no substantial systematic errors were left undetected. 

As mentioned before, two interlaboratory studies were organised prior to certification, involving ca. 15 laboratories using techniques such as cold vapour atomic absorption spectrometry, direct current plasma atomic emission spectrometry (DCP-AES), differential pulse anodic stripping voltammetry (DPASV), microwave plasma atomic emission spectrometry (MIP-AES), electrothermal atomic absorption spectrometry (ETAAS) and neutron activation analysis with radiochemical separation (RNAA). 

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