Highly Selective Detection of Silver in the Low ppt Range with Ion-Selective Electrodes Based on Ionophore-Doped Fluorous Membranes

Abstract

Ionophore-doped sensing membranes exhibit greater selectivities and wider measuring ranges if their membrane matrixes are noncoordinating and solvate interfering ions poorly. This is particularly true for fluorous phases, which are the least polar and polarizable condensed phases known. In this work, fluorous membrane matrixes were used to prepare silver ion-selective electrodes (ISEs). Sensing membranes composed of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate, and one of four fluorophilic Ag+-selective ionophores with one or two thioether groups were investigated. All electrodes exhibited Nernstian responses to Ag+ in a wide range of concentrations. Their selectivities for Ag+ over interfering ions were found to depend on host preorganization and the length of the –(CH2)n– spacers separating the coordinating thioether group from the strongly electron withdrawing perfluoroalkyl groups. ISEs based on the most selective of the four ionophores, i.e., 1,3-bis(perfluorodecylethylthiomethyl)benzene, provided much higher selectivities for Ag+ over many alkaline and heavy metal ions than most Ag+ ISEs reported in the literature (e.g., logKAg,Jpot for K+, −11.6; Pb2+, −10.2; Cu2+, −13.0; Cd2+, −13.2). Moreover, the use of this ionophore with a linear perfluorooligoether as membrane matrix and solid contacts consisting of three-dimensionally ordered macroporous (3DOM) carbon resulted in a detection limit for Ag+ of 4.1 ppt (3.8×10−11 M).

Potentiometric Sensors with Ion-Exchange Donnan Exclusion Membranes

“…5,6 Such membrane materials reject hydrophilic and hydrophobic species and represent an important new direction in ion sensor development.…”

Selective Transport of Silver(I) Cation Across a Bulk Liquid Membrane Containing Bis-β-enamino Ester as Ion Carrier

“…It has also been found that silver is toxic to humans at a concentration as high as 97.2 µg L -1 in drinking water. [7][8][9][10] On the other hand, owing to the fact that Ag + has moderate coordination ability, it is quite difficult to be discriminated from other chemically similar toxic elements. Therefore, separation and recovery of silver from waste and industrial sources are environmentally and economic important.…”

Silica gel/gold nanoparticles/(NS)2 ligand nanoporous platform-modified ionic liquid carbon paste electrode for potentiometric ultratrace assessment of Ag(I)

“…As a result, about 2500 tons of silver are released into the environment annually, and approximately 80 tons end up in surface waters (Ratte 1999;Mashhadizadeh et al 2013). Silver is not as toxic to humans as many other heavy metals, but the U.S. Environmental Protection Agency reported that a concentration higher than 1.6 nM is toxic to fish and microorganisms (Lai et al 2010) and the maximum contaminant level for total silver in drinking water was set to 0.9 lM, according to the Environmental Protection Agency in Washington DC of USA (1991).…”