Electroanalytical Determination of Arsenic(III) and Total Arsenic in 1 mol L−1HCl Using a Carbonaceous Electrode Without a Reducing Agent

Magnetite interaction with arsenic during sorptive removal from groundwater: a mechanistic study

A magnetic mixed iron oxide, magnetite (Fe₃O₄), was synthesized in the laboratory and characterized before its use as sorbent for arsenic removal. The characterization techniques used were X-ray diffraction (XRD), specific surface area, zeta potential and particle size measurements. The sorbent was applied for arsenic removal, without any pre or post treatment, from groundwater. The efficiency of sorption can only be improved by understanding the sorbent-sorbate interaction. For onsite monitoring of the sorbent-sorbate interaction, an electrochemical investigation using cyclic voltammetry (CV) measurement was developed. The study confirmed that the sorption of As(III) on Fe₃O₄ is dynamic (reversible) whereas that of As(V) is static (irreversible) in nature. Detailed investigation after the sorption was carried out utilizing X-ray photoelectron spectroscopy (XPS) measurement. The complexation of As(III)-Fe₃O₄ and As(V)-Fe₃O₄ without any redox transformation was evident from the XPS data. By careful examination of the results, a mechanism of arsenic removal by Fe₃O₄ was proposed.

A new strategy for the modification of a carbon paste electrode with carrageenan hydrogel for a sensitive and selective determination of arsenic in natural waters

An adsorptive stripping voltammetric method for the determination of As(III) and As_total in water samples using a carrageenan modified carbon paste electrode is presented for the first time (CAR-CPE). The modified electrode was prepared in different ways: by adding CAR in solid form or as a hydrogel together with graphite and paraffin, as well as adsorbing CAR by applying a potential on an unmodified carbon paste electrode. The best results were obtained when CAR was incorporated as hydrogel (HCAR-CPE). The selection of the ratio amounts for electrode preparation was carried out applying a multivariate experimental design. Variables like amount of graphite (U₁), HCAR (U₂) and paraffin (U₃) were optimized using a (2^K+2K+C) model. The results showed that the amount of HCAR was the most significant factor, and the adequate U₁:U₂:U₃ ratio to prepare the electrode was: 493 mg of graphite, 214 μL of paraffin and 134 μL of carrageenan as gel. The optimum parameters for the determination of As(III) were pH = 3.25 (0.01 mol L^-1 H₃PO₄/H₂PO₄^- solution); E_acc = -0.50 V and t_acc = 30 s. The electrode presents good linear behavior concentration range from 0.50 to 6.70 μg L^-1, with a limit of detection of 0.22 μg L^-1. The relative standard deviation was 5.0% at the 1.5 μg L^-1 As(III) level (n = 16). The method was validated by quantifying As(III) in spiked tap water from laboratory (RE: 3.0%), and it was applied for the determination of As_total in water samples from the Loa River (North of Chile) prior reduction of As(V) with Na₂S₂O₃ solution, obtaining 814.00 ± 0.03 μg L^-1. The results of the proposed method were compared with those obtained by adsorptive stripping voltammetry with HMDE and by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) techniques.

Inorganic arsenic speciation by differential pulse anodic stripping voltammetry using thoria nanoparticles-carbon paste electrodes

Two novel thoria (ThO2) nanoparticles-carbon paste electrodes were used to evaluate an anodic stripping voltammetric method for the direct determination of arsenite and total inorganic arsenic (arsenite plus arsenate) in water samples. The effect of Ag((I)), Cu((II)), Hg((II)), Sb((III)) and Se((IV)) ions on the electrochemical response of arsenic was assayed. The developed electroanalytical method offers a rapid procedure with improved analytical characteristics including good repeatability (3.4%) at low As((III)) concentrations, high selectivity, lower detection limit (0.1 μg L(-1)) and high sensitivity (0.54 μA μg(-1) L). The analytical capability of the optimized method was demonstrated by the determination of arsenic in certified reference materials (trace elements in natural water, trace elements in water and coal fly ash).