Higher Quaternary Ammonium Salts with a Sterically Hindered Exchange Center: Application to the Development of Ion Selective Electrodes Reversible to Metal Thiocyanate Complexes

Ion-selective electrodes based on a sterically hindered higher quaternary ammonium salt, 3,4,5-trisdodecyloxybenzyltrioctadecylammonium bromide, and a plasticizer, 1-bromonaphthalene, reversible to zinc and cobalt thiocyanate complexes, are developed. They are characterized by high analytical performance. The selective determination of zinc and cobalt on their simultaneous presence is achieved by varying the concentration of ligands (thiocyanate ions) in the supporting electrolyte. The mechanism of the coordination of thiocyanate ions with some d-metal cations was studied by IR spectroscopy. It is shown that zinc and cobalt coordinate SCN– ions by the isothiocyanate type, because of which Zn(NCS)₄^2 - and Co(NCS)_4^2 - ions have a high anion-exchange affinity to the membrane phase. The developed electrodes were used to determine zinc and cobalt in cheese, potatoes, and beets.