Maria Antonietta Baldo

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 1. Application to Wine

Differential-pulse anodic stripping voltammetry with a mercury microelectrode is used for the determination of zinc, cadmium, lead and copper in wine at its natural pH without pretreatment. The effects of the matrix on the stripping peaks are studied in detail by varying the concentration of the metals. Intermetallic (Cuue5f8Zn) interferences and the effects of oxygen are described. The results obtained for the labile metal contents varied from 2 μg l−1 for cadmium to 148 μg l−1 for zinc; standard addition plots were linear over about two orders of magnitude above these levels, demonstrating the negligible effect of organic matter. Acidification of the sample with hydrochloric acid to pH 1 allowed the total metal contents to be determined. The reliability of the method was tested by comparison with the results obtained with atomic absorption spectrometry; the differences were within 10–20%.

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l−1 Cu, 0.38 μg l−1 Pb, 0.01 μg l−1 Cd and 0.95 μg l−1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.

Anodic Stripping Voltammetry at Bismuth‐Coated and Uncoated Carbon Microdisk Electrodes: Application to Trace Metals Analysis in Food Samples

Abstract This article reports on the performance of a bismuth‐coated carbon microdisk electrode (BiFμE) for the determination of trace heavy metals by anodic stripping voltammetry (ASV). The BiFμE was prepared by electrodeposition of a metallic bismuth film onto the microdisk, by applying an in‐situ electroplating procedure. To test the performance of the BiFμE, ASV measurements were performed on synthetic solutions containing Cd2+, Pb2+, and Cu2+ as target ions. The results indicated that cadmium and lead gave well‐defined ASV peaks with no interference, and their quantitative determination could be carried out straightforwardly. In particular, linear calibration curves over the range 5.0 × 10−8–1.0 × 10−6 M for both ions, and detection limits of 7.8 and 2.9 nM, for cadmium and lead, respectively, after applying a 60 sec preconcentration step, were obtained. The reproducibility was also satisfactory, the relative standard deviation (RSD) being within 2.5% for both ions. Copper, instead, gave an ASV response that, in most experimental conditions, overlapped with that of bismuth. This circumstance made the determination of copper at the BiFμE difficult. Since the latter element could be detected reliably at the uncoated carbon microdisk electrode (CμE), both BiFμE and CμE were employed, respectively, for the determination of lead and copper ions in drinking water, wine, and tomato sauce.

Determination of Lead and Copper in Wine by Anodic Stripping Voltammetry With Mercury Microelectrodes: Assessment of the Influence of Sample Pretreatment Procedures

The results obtained using different pretreatment procedures for ndetermining total lead and copper in wine by anodic stripping voltammetry nwere compared. The measurements were performed by employing mercury nmicroelectrodes as the working electrode and linear sweep voltammetry as nthe voltammetric technique in the oxidation step. The pretreatments nconsidered were (A) wine plus concentrated HCl to pH 1.5; (B) wine plus n30% m/m H n 2 nO n 2 n (2.5:1 v/v) and UV irradiation for 2 h; nand (C) wine plus concentrated HCl to pH 1.5 and UV irradiation for 4 h. nThe three procedures gave different results, and the efficiency of the ndifferent procedures in releasing the cations from inorganic and organic ncomplexes can be ranked as B > C > A. Moreover, data obtained with nprocedure B agreed within 15% with the values found by AAS measurements. nFor the quantification of the metal ions, both the multiple standard naddition method, based on current or charge versus concentration ngraphs, and an absolute method, based on the charge involved in the nstripping peak, were employed. The latter procedure allowed measurements nto be carried out even when the calibration plots were not linear. When nall the quantitative methods could be applied, data agreement within 5% nwas found.

Linear sweep and cyclic voltammetry for metal deposition at solid and mercury microelectrodes from solutions with and without supporting electrolyte

Abstract The experimental behaviour under linear sweep and cyclic voltammetry at low scan rates of the reduction of Pb 2+ and Cd 2+ at solid and mercury microelectrodes is reported in the presence and in the absence of supporting electrolyte. The major effects observed on decreasing the concentration of supporting electrolyte are an increase in the steady-state limiting current and more drawn out curves during the direct scan, broader and asymmetric stripping peaks on the reverse scan. These effects are rationalized in terms of the contributions of migration associated with diffusion in the mass transport and ohmic polarization which adds to concentration polarization when the concentration of supporting electrolyte is decreased. The experimental results are also compared with theoretical predictions.

Voltammetric Probe of Milk samples by using a Platinum microelectrode

Abstract Milk is a complex heterogeneous fluid containing many components in several states of dispersion. When used as a bulk solvent for studying electrochemical processes of some of the electroactive species present, it displayed mainly aqueous solution properties. With microelectrodes (25 μm in diameter) some typical constituents can be detected and the reproducibility of the processes studied was found to be satisfactory, with relative standard deviations (r.s.d.s.) lower than 2%, whereas measurements with conventional-sized platinum electrode (3 mm in diameter) gave r.s.d.s, of about 10%. Moreover, because of enhanced mass transport associated with the smallest electrodes, it was possible to diagnose the formation of precipitates of calcium phosphates on the electrode surface, as a consequence of a CEC electrode process at −0.920 V vs. SCE, involving protons released by H 2 PO − 4 , HPO 2− 4 formed in the electrode reaction and Ca 2+ . The reduction of acidic groups from casein, the oxidation of ascorbate and oxygen effects were also studied.

Amperometric end-point detection of complexometric titrations with platinum microelectrodes

An amperometric method is proposed for end-point detection of complexometric titrations of metal ions in unbuffered solutions with disodium ethylenediaminetetraacetate (Na2H2Y). It is based on the use of a platinum disc microelectrode as a sensor for monitoring the hydrogen ions delivered during the titration. Synthetic solutions containing Ca2+ and Mg2+ ions, each alone or in mixture, are examined. The method is also applied to the determination of the total concentration of Ca2+ and Mg2+, i.e., the total hardness, in mineral and tap waters. The precision of the method is satisfactory, the relative standard deviation being not greater than 2% for at least three replicates. Comparative measurements performed by the classical procedures using a metallochromic indicator give data agreement within 3.5%.

The Ion Interaction Reversed Phase High-Performance Liquid Chromatography and the Voltammetry With Microelectrodes In the Analysis of Milk

Abstract Some anionic species present at the natural pH of milk (6.72), namely hydrogen-orthophosphate, L(+)-ascorbate and hydrogencitrate were detected in samples of crude bovine-milk both by ion interaction reverse phase HPLC chromatography and by amperometry based on microelectrodes. The RSD ranged between 2 and 5 % for the former technique and between 3 and 4 % for the latter. the accuracy was evaluated by comparing the data obtained with the two techniques and discrepancies between the methods never exceeded 9% .