The Selective Extraction and Spectrophotometric Determination of Copper and Silver by the Use of a Thiocrown Compound 1,4,8,11-Tetrathiacyclotetradecane

Abstract

Abstract A highly selective solvent extraction and spectrophotometric determination of copper and/or silver is proposed; it is based on the extraction of the ion-pair formed by the copper(I)- or silver(I)-thiocrown ether complex cation and the appropriate dye anion. A comparative study of Bromocresol Green (BCG), Thymol Blue (TB), and picrate ions as the pairing ions for the extraction of copper using a 1,4,8,11-tetrathiacyclotetradecane (TTCT) solution of 1,2-dichloroethane is described. The use of BCG gave the highest sensitivity among these three kinds of anions and made it possible to determine copper in the range of 0.6–3.2 μg ml−1. The interferences of six kinds of cations and four kinds of anions were examined; only Ni2+ and ClO4− interfered, and they slightly. The separation by the extraction of silver and/or copper with TTCT solution of 1,2-dichloroethane from an aqueous solution containing seven kinds of metal ions (Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Ag+) in the presence of picrate ion (Pic−) was also examined. Silver was first extracted quantitatively as the ion-pair compound, [Ag(ttct)2]+Pic−, and then copper as [Cu(ttct)]+Pic− after having been reduced to copper(I). The absorption maximum of both extracted species lies at 378 nm (ε:1.8×104), and the spectrophotometric determination of these metals is possible. This method was successfully applied to the determination of copper and silver in standard samples of steel.