Determination of gold using anion‐exchange‐based chemically modified electrodes

Abstract

The determination of gold by the application of electrodes modified with anion exchangers is considered. Particular attention is paid to investigating the capability of these electrodes to determine gold(II1) in the presence of copper(I1). Electrodes modified with a film of poly(4-vinyl-pyridine) or either chemisorbed electrochemically generated were investigated. It was found that copper(I1) caused little or no interference in chloride media. However, copper( 11) cyanide complexes interfered with the determination of gold cyanide solutions. llvTRODUCT1ONThe development of new analytical methods capable of determining trace levels of gold remains an area of interest [l-71. In particular, the development of a method suitable for use in the analysis of refinery plant effluents, to minimize processing losses, or to analyze groundwaters for geological exploration purposes is an attractive proposition.Voltammetric methods, especially anodic stripping voltammetry (ASV), are well suited to the determination of gold. ASV is relatively inexpensive, has adequate sensitivity, and can be operated for on-line analysis [8] or as a portable unit [2]. However, problems arise with the use of ASV for gold analysis in the presence of copper. The tendency of gold and copper to form an amalgam during the electrodeposition step leads to erroneously high analytical results. Therefore, to accurately quantify gold in the presence of copper, it is necessary to perform a chemical separation, usually using solvent extraction, prior to analysis 17, 91. The chemical separation step adds a further degree of complexity to the ASV laboratory method and makes the adoption of the method to on-line or field use more difficult.To solve interference problems such as those described above, various research groups have addressed the development of chemically modified electrodes (CMEs) [ 10-131. Various electrode modifiers have been used to induce nonelectrochemical preconcentration methods prior to voltammetric analysis. For example, electrodes that achieve preconcentration via complex-' To whom correspondence should be addressed. The use of CMEs has also been investigated for the determination of gold [4, 121. Workers in this area were not particularly concerned with overcoming the gold/ copper selectivity problem; however, they did employ electrodes capable of ionexchange preconcentration to enable gold to be determined using an electrochemical reduction process. Both studies employed carbon paste electrodes, into which an anion exchanger could be incorporated.In the course of this work, a CME capable of overcoming the goldkopper selectivity problems was developed. The active component of the electrode is poly(4-vinylpyridine) (PVP), which is known [ 171 to prefer binding anionic gold species over anionic copper species. The use of both chemically and electrochemically generated PW-based polymers was considered. The effect of polymer thickness, the electrochemical stripping waveform, and the presence of copper on the gold response were taken ...

Catalytic Effect on Silver Electrodeposition of Gold Deposited on Carbon Electrodes

“…These values are comparable with those obtained on a glassy carbon electrode either coated with a film of poly(4-vinyl-pyridine) [10] or in the presence of yeast mannan [11] and on carbon fibers [12].…”

Double Deposition and Stripping Steps for Trace Determination of Au(III) Using Anodic Stripping Voltammetry

“…Because the above methods require sophisticated and expensive instruments electrochemical methods are a competitive alternative as concerns heavy metals ions determination on trace and ultratrace levels. Anodic (ASV) and Cathodic (CSV) Stripping Voltammetry were applied for gold determination using various working electrodes to determine gold ions, among them a glassy carbon electrode 8–10, a chemically modified carbon paste electrode 11–17, the chemically modified electrodes 18–20, a modified screen printed carbon electrode 21, the electrodes modified with anion exchangers 22, the carbon fiber ultramicroelectrodes 23, a lab‐on‐paper electrode 24 and a tannin‐immobilized non‐conducting electrode 25. The determination of gold at the commonly used mercury electrodes is usually not possible by anodic stripping voltammetry because the stripping peak occurs at a potential which is more positive than the anodic dissolution of mercury 26.…”

Method for determination of gold in solutions with high oxidation/reduction potential

“…All these solutions have high ORP (EoxIred > 0.9 V) All the described methods for gold analysis [4,5,6, 71 can be used in a solution with special pH and special composition. One of the most important problems in applying these methods for analysis of a solution with high ORP, is the destruction of a sensor in this solution.…”

“…At the present time, the most environmentally clean methods for dissolving gold, extracted from gold-containing materials, are non-cyanide methods, including methods of dissolving in aqua regia [ 11, hypochlorite-iodine mixture [2], or bromine solution [3]. All these solutions have high ORP (EoxIred > 0.9 V) All the described methods for gold analysis [4,5,6,71 can be used in a solution with special pH and special composition. One of the most important problems in applying these methods for analysis of a solution with high ORP, is the destruction of a sensor in this solution.…”