Potentiometric determination of mercury(II) and thiourea in strong acid solution using an ion-selective electrode with AgI-based membrane hydrophobised by PTFE

Summary The potentiometric determination of mercury(II) and thiourea (TU) in strong acid solution (pH 0–1) by using an all-solid-state ion-selective electrode with (Ag₂S 25%, AgI 25% and PTFE 50% m/m)-membrane is described. The linear response, 43 mV(pHg)^–1 and 80 mV(pTU)^–1, has been obtained in the concentration range from 10^–2 to under 10^–5 mol/l. By direct potentiometry at pH 0 mercury(II) can be determined in the presence of up to 10^–3 mol/l of iron(III). The change in potential in the tested concentration range of thiourea indicates the formation of Ag(TU)_1.4⁺at the exposed surface of the membrane. This stoichiometry is in good agreement with that calculated from the average Ag/TU ratio in the potentiometric titration. The investigated electrode can be used as a good sensor for mercury(II) and thiourea in strong acid media and a wide variety of practical analytical systems.