POTENTIOMETRIC DETERMINATION OF MERCURY(II) AND THIOUREA IN STRONG ACID-SOLUTION USING AN ION-SELECTIVE ELECTRODE WITH AGI-BASED MEMBRANE HYDROPHOBIZED BY PTFE

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.