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Potentiometric Studies on Chemically and Electrochemically Prepared Sulfide Active Materials for Determination of Copper(II)

Three electrodes have been prepared by mixing and pressing different materials: Ag2S + Cu (electrode 1) ; Ag + Cu (electrode 2) ; pure Cu powder (electrode 3). Prepared electrodes were chemically or electrochemically sulfidated and its suitability for potentiometric determination of Cu2+, in water and mixed organic solvent-water solutions, have been investigated. Depending on electrode composition, differences in potentiometric characteristics between chemically prepared sensitive layers were noticed. Unexpected potentiometric behaviors, including deterioration in linear range, deterioration in detection limit (for chemically sulfidated electrode 1 and electrode 2) and super-Nernstian behavior (only for chemically sulfidated electrode 1) are observed and explained by physical characteristics of the prepared sulfide layers. Also, processes responsible for these behaviors are suggested and explained.. Improvements in potentiometric characteristics, for electrodes with electrochemically prepared sulfide layers, when compare to untreated and chemically treated electrodes are reported. Obtained detection limit, linear range and slope, for electrochemically sulfidated electrode 1 were 1.5 × 10-7 M, 3.0 × 10-7 - 0.1 M and 29.5 mV dec 1, respectively. These improvements are discussed in the light of physical and chemical processes that take place in sensitive layers and electrode bulk. In addition, study performed in solutions containing different acetonitrile-water ratio revealed that not only solubility of CuxS, but also Ag2S leaching (which depends on the nature and a way of its incorporation in membrane) is responsible for super-Nernstian responses in mixed solvents. Also, comments to appearance of the super-Nernstian response with increasing acetonitrile content are given.

chemical and electrochemical sulfidation; potentiometry; mixed organic solvent-water solutions; super-Nernstian

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