Potentiometric determination of thiourea (TU) in strongly acidic solution (pH=l) by using "all-solid-state" ion-selective electrode with (Ag2S 25%, AgI 25% and PTFE 50% m/m) - membrane is described. The utilized sensing electrode has been prepared in the laboratory. The equilibrium potentials observed during serial dilution or standard addition, under constant pH and ionic strength, are plotted against log c(TU). A linear response with a slope 80 mV (pTU)-1 has been obtained in the concentration range from 10^2 to 10-5 mol dm-3 The change in potential, in tested concentration range of thiourea, indicates Ag(TU)x+ formation at the exposed surface of membrane. The maximum response time of the potential cell with electrode was 1 min. even at low concentrations of thiourea. The electrode reached a steady-state potential (drift 0, 3 mV min-1) within the time of experiments. In all experiments the potential drifts were-parallel and relatively small.

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