The Liquid Membranes of the Thiocyanate Ion-Sensitive Electrode

Ion-selective electrode membranes responsive to the thiocyanate ion were prepared by using ion-association extraction systems. A crystal violet or tetraphenylarsonium cation was used as an ion exchange-site in the liquid nitrobenzene membrane. The liquid membrane electrode exhibits an ideal Nernstian response to the thiocyanate ion down to 10−5 M. The selectivity of the liquid membrane largely depends on the extractability of the diverse anion into nitrobenzene. The order of the selectivity coefficients, Kj, is as follows: ClO_4^->IO_4^->SCN^->I^->ClO_3^->NO_3^->Br^->BrO_3^->Cl^- High selectivities for thiocyanate over SO42−, H2PO4−, Cl−, BrO3−, and Br were observed. The membrane potential is independent of the pH variation in the region from pH 2 to 12.