Chunze Lai, Ph.D.
Introduction: A novel highly selective sensor for silver is described below. This sensor is based on Teflon®like matrixes and a new fluorophilic silver receptors.
Background: Silver is utilized for a wide range of applications. Due to their antibacterial properties, silver salts and silver nanoparticles are used for the disinfection of drinking water and the preparation of topical gels, specialty bandages, implantable prostheses, and catheters. Every year, about 2500 tons of silver are released into the environment and approximately 80 tons end up in surface waters. Although silver is not as toxic to humans as many other heavy metals, the U.S. Environmental Protection Agency has set the maximum contaminant level for total silver in drinking water to 0.9 ?M. While other methods for the determination of silver are available, such as atomic absorption spectrometry, and the use of an inductively coupled plasma in combination with atomic emission or mass spectrometry, these techniques often require quite extensive and time-consuming sample pretreatment, including preconcentration and matrix separation. In comparison, ion-selective electrodes require little sample preparation and manipulation while still permitting very wide ranges of linear response, low limits of detection, high selectivities, and the possibility to distinguish between the free metal ion and its complexes.
Method: Our sensors take advantage of the highly selective and fouling-resistant fluorous membranes licensed from the University of Minnesota. Fluorous phase has extremely low polarity and is immiscible with either aqueous phase or organic phase, therefore, lowering the solvation of interferences in the membrane phase. To develop fluorous silver electrodes, a series fluorophilic silver ionophores with one or two thioether groups were tested and their selectivities for silver 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. The best ionophore provided much higher selectivities for Ag+ over many alkaline and heavy metal ions than most silver ISEs reported in the literature (e.g., 10 orders of magnitude more selective than Pb2+, 13 orders of magnitude more selective than Cu2+ and Cd2+). Combing the benefit of the high selectivity from fluorous membrane and the elimination of transmembrane ion fluxes from solid-contact electrode setup, a detection limit for silver of 4.1 ppt (3.8 × 10?11 M) has been achieved, and this is the lowest detection limit has ever been reported for silver sensor.
Application: Our fluorous silver sensors could be used in a wide variety of matrixes, such as waste water and drinking water, wetlands. Ongoing research will expand the application of the electrode to measure in blood and food.