An arrangement of a voltammetric cell specially designed to be compatible to both centrifugation and voltammetry was designed, allowing direct measurement without any need for dissolution or filtration steps. The procedure for the preconcentration via coprecipitation is described. The system was succesfully tested using trace amounts of Pb(II) ions in aqueous solution preconcentrated with Al(OH) 3 as the carrier precipitate and resulting peak currents were found much higher than those without applying centrifugation. The effects of the parameters on the resulting signal were examined and the detection limit was found as 2.2 Â 10 À9 M. The present study demonstrates a novel procedure which combines the advantages of coprecipitation with those of anodic stripping voltammetry in a single cell. For this purpose, a vessel compatible to both a voltammetric analyzer and centrifuge was constructed. A planar electrode was placed at the bottom of the cell in order to accumulate a thin layer of adsorptive materials onto the surface by centrifugation. First experiments with this cell include voltammetric determination of Pb(II) ions with the help of preconcentration via coprecipitation thus avoiding the filtration and dissolution steps.Al(OH) 3 is widely used as a collector precipitate. A thin layer of Al(OH) 3 produced by centrifugation at the electrode surface can adsorbe and therefore preconcentrate trace elements. The main objective of the study is to trap the analyte, i.e., lead ion, between the alumina layer and the electrode surface by coprecipitation. It also provides a conductive coating which allows for the voltammetric measurement directly in the same cell eliminating labourous filtration and dissolution steps.A previous study on preconcentration recommends the use of 200 mg aluminum salt per 200 mL solution for Pb(II) enrichment [7]. This value reflects the maximum amount of Pb(II) ions carried by the precipitate for optimal separation. In terms of sensitivity, the optimization of Al(III) concentration that will yield the maximum peak current for lead ions is necessary for the present work. Among the concentrations examined, best results for enriched Pb(II) ions were obtained with 5 Â 10 À5 M Al(III) solution (data not shown). Higher concentrations produce a thicker aluminum hydroxide layer on the electrode surface that will render the reduction process of Pb(II) ions trapped.As is well known, the medium pH influences the amount and adsorption capacity of the precipitate. Upon addition of aluminum salts to the aqueus solution, hydrolysis reactions take place leading to the formation of monomers and multinuclear hydrolyzed species depending on the pH of the medium [8]. Therefore, the pH effect was examined in a

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Centri-voltammetry is a method developed in the last decade which combines the advantages of centrifugation and voltammetry and hence provides a practical way for application of co-precipitation in trace analysis allowing direct voltammetric scan. The present study describes another application of the centri-voltammetric method for the determination of biologically essential trace elements, in particular, molybdenum ion. For this purpose, a dual-functional voltammetric cell adjustable to the centrifuge was designed and utilized in the determination of molybdenum ions with various carrier reagents, i.e. oxine, pyrogallol red, and cupferron. Optimization studies include solution properties as well as voltammetric measurement and centrifugal parameters. Among the reagents studied, the best results were obtained with pyrogallol red and the reduction peak current of the complex was utilized for analytical purposes. The limit of detection from calibration curves was calculated to be 9.4 Â 10 À9 M and a better sensitivity was obtained in the presence of chlorate ions that are known to have a catalytic effect on the reaction. The method was employed in the determination of molybdenum in milk samples and the results were compared with those obtained by the ICP-MS method.

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