Selective determination of trace amounts of silver in complicated matrices by displacement-cloud point extraction coupled with thermospray flame furnace atomic absorption spectrometry

Abstract

A novel displacement-cloud point extraction approach was developed for the selective determination of trace silver in complicated matrices by thermospray flame furnace atomic absorption spectrometry. This method involves two steps of cloud point extraction, i.e., firstly, copper ion reacts with diethyldithiocarbamate (DDTC) to form Cu-DDTC before it is extracted; secondly, after removing the aqueous phase, a sample or standard solution containing silver ion is added and another cloud point extraction procedure is carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag⁺ can displace Cu²⁺ from the pre-extracted Cu-DDTC and thus the preconcentration and separation of Ag⁺ from complicated sample matrix is achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu²⁺ from Cu-DDTC complex. Up to 5000 μg mL⁻¹Ni(II), 2000 μg mL⁻¹ Cd(II), 1000 μg mL⁻¹Fe(III), 2000 μg mL⁻¹Co(II), 5000 μg mL⁻¹Zn(II) and 5000 μg mL⁻¹Mn(II) caused no significant interference with the determination of silver of 5 μg L⁻¹. Compared with conventional cloud point extraction, the tolerance limit for the co-existing transition metal ions was increased by at least two orders of magnitude. Under the optimal chemical and instrumental conditions, the limit of detection was 0.2 μg L⁻¹ for silver with a sample volume of 10 mL, and a sensitivity enhancement factor of 21 was achieved. The proposed method was successfully applied to interference-free determination of trace silver in soil, marine sediment and ore samples with high contents of co-existing heavy metals.