Use of dicyclohexano-18-crown-6 to separate traces of silver(I) from potassium thiocyanate in hydrochloric acid media, and determination of the silver by atomic absorption spectrometry

Abstract.

Solvent extraction with 0.05 mol L^–1 dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane, coupled with flame atomic absorption spectrometry (AAS), has been investigated as a new method for separation of trace amounts of silver(I) from 0.05 mol L^–1 potassium thiocyanate in 1.0 mol L^–1 hydrochloric acid media and quantification of the amount of silver present. The method is based on the formation of an extractable ion-association product, [DC18C6·K]⁺[Ag(SCN)₂]^–, with a metal-to-crown ether ratio of 1:1 (as derived from slope analysis data). Stripping of the extracted silver(I) in the 1,2-dichloroethane phase was achieved within 5 min by use of 3.0 mol L^–1 potassium thiocyanate. Reducing the concentration of acid in the sample solution to 0.1 mol L^–1 improved the preconcentration factor severalfold. Excellent tolerance of the proposed method to the presence of foreign ions in solution with silver(I) was demonstrated. A detection limit of 13 ng mL^–1 was derived from the mean value of the blank plus three times its standard deviation. The method was used to determine traces of silver(I) after separation from gold(III), platinum(IV), and palladium(II) matrices on the basis of extractability differences with 18-membered crown ethers under specified conditions. The efficiency of the adopted ion-association mechanism for silver(I) extraction was apparent from the average recovery of 96% for spiked standards by use of the back-washing technique. The proposed extraction procedure was applied to the determination of traces of silver(I) in a selection of chemical reagents.