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A comparison is made between two 'dual activation' electroanalytical techniques for the detection and measurement of vitamin C (L-ascorbic acid) in a commercially available fruit drink via its two electron oxidation at platinum electrodes. Glucose is found not to interfere with the analytical response. First in sonovoltammetry pulses of 25 Wcm ¹2 are applied and the current response characterized in the 'pulse off' period where a current plateau is attained. Second in laser activated voltammetry a 10 Hz pulsed laser (532 nm, ca. 240 Wcm ¹2 average intensity) is used to 'burn' surface adsorbed passivating species off the electrode. Both methods cause agitation of the solution in the bulk phase or at the electrode-solution interface and lead to regular renewal of the diffusion layer. The mass transport limited oxidation currents so obtained are found to scale with ascorbic acid concentration in media where electroanalysis without simultaneous ultrasonic or laser stimulation may be precluded due to electrode passivation. Application to the quantitative electroanalysis of ascorbic acid in the fruit drinks Ribena and 'No added sugar' Ribena is reported. The results obtained are in excellent agreement with those yielded by independent chemical and electrochemical methods.

To in situ remediate rivers polluted by organic matter and heavy metals, lab-scale sediment microbial fuel cells (SMFCs) were operated under different conditions.

The electroanalytical detection of L-ascorbic acid via its two electron oxidation in aqueous solution is the subject of a comparison of two voltammetric methodologies both of which rely in part on electrode abrasion. First in sonovoltammetry cavitational collapse at the electrodesolution interface can lead to electrode erosion and activation. Second in laser ablation voltammetry (LAV) a 10 Hz pulsed laser (532 nm, 0.7 mJ per pulse) is used to abrade the electrode. In both cases the concomitant agitation of the solution leads to regular refreshment of the diffusion layer so that at sufficiently extreme potentials sustained currents (transport limited currents) are observed which scale with the concentration of ascorbic acid present and permit quantitative electroanalysis.Comparison of the methods as applied to ascorbic acid shows that for LAV the laser light intensity can be adjusted for maximum ablation of surface adsorbed blocking species but with minimum damage to the platinum surface itself. In contrast the sonovoltammetry technique does not facilitate selective erosion of surface adsorbed species. Instead the mass transport, amount of cavitation and damage to the electrode are all interlinked with the intensity of ultrasound employed. Thus while the amount of cavitation at the electrode surface can be controlled the relative adsorbate/electrode abrasion cannot. The limiting currents under insonation were found to be substantially (ca. 15 times) larger than for LAV suggesting that the major benefit of sonovoltammetry is in terms of enhanced mass transport whereas LAV shows more selective cleaning activation. The development of a novel sono-LAV is therefore reported which retains the merits of both the separate experiments in isolation. Thus the cleaning potential of LAV is coupled with the mass transport enhancement of ultrasound. Application to the quantitative electroanalysis of ascorbic acid is reported.

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