DEVELOPMENT OF ULTRASENSITIVE VOLTAMMETRIC ION-SELECTIVE ELECTRODES

DEVELOPMENT OF ULTRASENSITIVE\ud VOLTAMMETRIC ION-SELECTIVE ELECTRODES\ud Mohammed Basem Garada, M.S.\ud University of Pittsburgh, 2015\ud \ud \ud Low concentration detection of ions is an important part of many industrial and medical fields. While current technologies in the form of ion chromatography and LC/MS present a reliable means of sensitive ion detection, they also can be quite expensive and bulky, and thus not always readily available to those who need them. Ion-selective electrodes offer a good alternative in the form of cheaper and smaller tools for ion detection. Most importantly, the level of detection of ion-selective electrodes can match that of more expensive methods and in some cases go beyond them. Through ion-transfer voltammetry ultrasensitive electrodes are created and used to be able to detect ions at sub-nanomolar levels. The specific electrodes used here consist of a gold electrode coated by an ion-to-electron transducing conducting polymer further overlain with an ionophore-doped organic PVC membrane. Various types of ions have been studied by both cyclic voltammetry and stripping voltammetry, including hydrophilic inorganic ions (Ca2+), hydrophobic organic surfactants (PFOS-) and biologically relevant macromolecules (protamine20+). Detection of surfactants is highlighted here, with an emphasis on an achievable detection limit of 50pM for PFOS- without any ionophore. This detection limit which is in fact lower than the EPA minimum reporting level was made possible due to the very high lipophilicity of PFOS- which allows it to be concentrated into the organic PVC layer to a greater extent during ion-transfer stripping voltammetry. Other surfactants including alkyl carboxylates, alkyl sulfonates and perfluorinated carboxylates were also tested, but a focus was made on PFOS- due to it being the most lipophilic on the EPA’s list of environmentally important surfactants. It was found that the conducting polymer used for surfactant detection, POT, led to oxidation of certain carboxylate surfactants. Previous issues of reduction of certain cations like Ag+ and Pb2+ with the other conducting polymer used, PEDOT, as well as lack of a stable potential for both POT and PEDOT led us to synthesize and electrochemically polymerize a new conducting polymer, 4,4’-dibutoxy-2,2’-bithiophene. This marks the first such electrochemical polymerization of this dimer. \u