Potentiometric Determination of Thallium Ions Using Carbon Paste Electrode by 18-Crown-6 as a modifier

Potentiometric method, using ion-selective electrodes, in comparison to other analytical methods, such as atomic absorption spectroscopy, chromatography, etc, has the advantages such as ease of use, speed and low cost. In this design, a sensitive and selective electrode was designed to measure thallium ion. The response of this electrode in the range of 10-7 to10-3 molar concentration of thallium is a Nernstian response. The sensor has a detector value of 5×10-8 molar. From an environmental point of view, toxicity of thallium (I) is a problem. Thallium(I) compounds, such as thallium sulfate, thallium acetate and thallium carbonate are toxic. Therefore, ion-selective electrode is one of the best and easiest methods for measuring thallium ion concentration. The response time of this sensor is about 40 seconds. The optimal membrane structure, which resulted in favorable results, was 72.59% graphite, 1.2% (18- crown-6) ionophore, 1.27%sodium tetra phenyl borate and 24.25% paraffin, that has the best Nernstian tilt of 57.07±1.09. After several tests, it was found that the electrode response does not depend on pH changes in (5 – 7) PH range. The electrode can be susceptible for 21 days and has an acceptable response to thallium concentration changes. The sensor was also used as the detector electrode in the potentiometric titration with EDTA and the results were in good agreement with the actual value.