A New Procedure for Voltammetric Lead Determination Based on Coprecipitation and Centrifugation Preconcentration

Abstract

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

Centri‐Voltammetric Folic Acid Detection

“…Up to this amount, the increase in current can be attributed to more carrier material will carry more analyte onto the electrode surface. Meanwhile, the decrease in the current value might be due to the polylayer formation of carrier material onto the electrode surface which rendered the oxidation process of FA that was trapped into these layers [29,30].…”

“…By applying centrifuga-tion, the analyte is deposited onto the electrode surface and without engaging any separation techniques, the analyte's redox behaviour is monitored voltammetrically [28]. Up to now, metallic substances [29,30] together with biologically important analytes [31,32,33,34,35] were detected by this method. Also, the electrode was modified with suitable enzymes [36,37] or cell lines [38] and various biocentri-voltammetric methods were developed.…”

“…Also, the electrode was modified with suitable enzymes [36,37] or cell lines [38] and various biocentri-voltammetric methods were developed. This method can be applied with [30,34,39,40] or without [29,[31][32][33][36][37][38] a carrier material. As mentioned above, in the present study, an accumulation step followed by a stripping step included centri-voltammetry was applied for FA detection.…”

Combination of a poly(3,4-ethylene-dioxythiophene) electrode in the presence of sodium dodecyl sulfate with centri-voltammetry

“…At this point, it is not possible to state the exact reason but these two explanations seem reasonable to us. On the other hand, current decrease at the higher speeds might be due to destruction of analyte layer that was on the electrode surface [30][31][32]36,38,39 . All optimization of centrifugal parameters experiments were performed in presence of 5.0x10 -5 M DA in 6.7x10 -2 M pH:7 PBS.…”

“…The effects of different amount of SDS on the sensor response for 5Optimization of centrifugal parameters: The centrifugation parameters are very important in centri-voltammetry[30][31][32][33][34][35][36][37][38][39] . In this study, SDS molecules should be deposited onto electrode surface in order to obtain electrostatic interaction with DA.…”