Browsing by Author "Neshkova M."

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    A new generation of cyanide ion-selective membranes for flow injection application. Part III. A simple approach to the determination of toxic metal-cyanide complexes without preliminary separation
    (2008-08-15) Surleva A.; Neshkova M.
    A new flow injection approach to total weak acid-dissociable (WAD) metal-cyanide complexes is proposed, which eliminates the need of a separation step (such as gas diffusion or pervaporation) prior to the detection. The cornerstone of the new methodology is based on the highly selective flow-injection potentiometric detection (FIPD) system that makes use of thin-layer electroplated silver chalcogenide ion-selective membranes of non-trivial composition and surface morphology: Ag2 + δSe1 - xTex and Ag2 + δSe. An inherent feature of the FIP-detectors is their specific response to the sum of simple CN- + Zn(CN)4 2- + Cd(CN)4 2-. For total WAD cyanide determination, ligand exchange (LE) and a newly developed electrochemical pre-treatment procedure for release of the bound cyanide were used. The LE pre-treatment ensures complete recovery only when the sample does not contain Hg(CN)4 2-. This limitation is overcome by implementing electrochemical pre-treatment which liberates completely the bound WAD cyanide through cathodic reduction of the complexed metal ions. A complete recovery of toxic WAD cyanide is achieved in the concentration range from 156 μg L-1 up to 13 mg L-1. A three-step protocol for individual and group WAD cyanide speciation is proposed for the first time. The speciation protocol comprises three successive measurements: (i) of non-treated, (ii) LE-exchange pre-treated; (iii) electrochemically pre-treated sample. In the presence of all WAD complexes this procedure provides complete recovery of the total bound cyanide along with its quantitative differentiation into the following groups: (1) Hg(CN)4 2-; (2) CN- + Cd(CN)4 2- + Zn(CN)4 2-; (3) Cu(CN)4 3- + Ni(CN)4 2- + Ag(CN)2 -. The presence of a 100-fold excess in total of the following ions: CO3 2-, SCN-, NH4 +, SO4 2- and Cl- does not interferes. Thus the proposed approach offers a step ahead to meeting the ever increasing demand for cyanide-species-specific methods. The equipment simplicity makes the procedure a good candidate for implementing in portable devices for in-field cyanide monitoring. © 2008 Elsevier B.V. All rights reserved.