Speciation of Cr(VI) and Cr(III) in Water Samples by Adsorptive Stripping Voltammetry in the Presence of Pyrogallol Red Applying a Selective Accumulation Potential

International journal of electrochemical science (Impact Factor: 1.5). 01/2012; 7(11):11444 - 11455.


An adsorptive stripping voltammetric procedure for the speciation of Cr(VI) and Cr(III) in the presence of pyrogallol red (PGR) is presented. The method is based on the previous reduction of Cr(VI) to Cr(III) at the electrode surface, its complexation with PGR, and the later reduction of CrIII−PGR to CrII−PGR at −0.85 V. The effects of various operational parameters such as pH, ligand concentration (CPGR), and accumulation potential and time (Eads, tads) were optimized. These studies were carried out using individual Cr(VI) and Cr(III) solutions and also mixtures of them. The results showed that the proper choice of the adsorptive potential produces selectivity for Cr(VI) in the presence of Cr(III). At an Eads of 0.00 V only Cr(VI) produces the reduction signal of CrIII−PGR at −0.85 V, while at an Eads of −0.68 V both Cr(VI) and Cr(III) produce this signal. Total chromium was determined after oxidation of Cr(III) to Cr(VI) by UV radiation in the presence of H2O2. The concentration of Cr(III) was evaluated as the difference between total chromium and Cr(VI). Under the best experimental conditions (pH 4.5; CPGR 0.25 μmol L−1; Eads −0.68 V and tads 60 s), the peak current is proportional to the total Cr concentration up to 20.0 μg L–1, with a 3 detection limit of 0.05 μg L–1. The relative standard deviation for a Cr(VI) solution (9.8 μg L−1) was 1.8 % for six successive assays. The method was validated using synthetic sea water (ASTM D665) spiked with Cr(VI) and Cr(III), and with a certified reference water (NCS ZC76307). In this reference material total chromium was determined as Cr(III) other aliquot of reference sample was oxidized and the total chromium determined as Cr(VI). Finally, the method was applied to the determination of Cr(VI) and Cr(III) in sea water samples

Download full-text


Available from: Nagles Edgar,
  • [Show abstract] [Hide abstract]
    ABSTRACT: Chronoamperometric assays based on tyrosinase and glucose oxidase (GOx) inactivation have been developed for the monitoring of Cr(III) and Cr(VI). Tyrosinase was immobilized by crosslinking on screen-printed carbon electrodes (SPCEs) containing tetrathiafulvalene (TTF) as electron transfer mediator. The tyrosinase/SPCTTFE response to pyrocatechol is inhibited by Cr(III). This process, that is not affected by Cr(VI), allows the determination of Cr(III) with a capability of detection of 2.0±0.2μM and a reproducibility of 5.5%. GOx modified screen-printed carbon platinised electrodes (SPCPtEs) were developed for the selective determination of Cr(VI) using ferricyanide as redox mediator. The biosensor was able to discriminate two different oxidation states of chromium being able to reject Cr(III) and to detect the toxic species Cr(VI). Chronoamperometric response of the biosensor towards glucose decreases with the presence of Cr(VI), with a capability of detection of 90.5±7.6nM and a reproducibility of 6.2%. A bipotentiostatic chronoamperometric biosensor was finally developed using a tyrosinase/SPCTTFE and a GOx/SPCPtE connected in array mode for the simultaneous determination of Cr(III) and Cr(VI) in spiked tap water and in waste water from a tannery factory samples.
    Analytica Chimica Acta 06/2014; 833. DOI:10.1016/j.aca.2014.05.006 · 4.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Most of the metal ions are carcinogens and lead to serious health concerns by producing free radicals. Hence, fast and accurate detection of metal ions has become a critical issue. Among various metal ions arsenic, cadmium, lead, mercury and chromium are considered to be highly toxic. To detect these metal ions, electrochemical biosensors with interfaces such as microorganisms, enzymes, microspheres, nano-materials like gold, silver nanoparticles, CNTs, and metal oxides have been developed. Among these, nanomaterials are considered to be most promising, owing to their strong adsorption, fast electron transfer kinetics, and biocompatibility, which are very apt for biosensing applications. The coupling of electrochemical techniques with nanomaterials has enhanced the sensitivity, limit of detection, and robustness of the sensors. In this review, toxicity mechanisms of various metal ions and their relationship towards the induction of oxidative stress have been summarized. Also, electrochemical biosensors employed in the detection of metal ions with various interfaces have been highlighted.
    Sensors and Actuators B Chemical 07/2015; 213:515-533. DOI:10.1016/j.snb.2015.02.122 · 4.10 Impact Factor