Determination of copper(II) and iron(III) by EDTA using pyrite electrode

The results obtained in the potentiometric titrations of copper(II) and iron(III) with standard EDTA solutions are presented. Titrations of copper(II), at pH values in the range from 8.11 to 10.99 (ammonia buffer), and of iron(III), at pH values from 3.59 to 5.65 (acetate buffer), were performed. The titration end-point (TEP) was detected with an indicator electrode from natural crystalline pyrite as an electrochemical sensor. The results obtained in the potentiometric titrations with the pyrite electrode were compared with those obtained using a platinum electrode (Fe3+) and a Cu-ISE (Cu2+). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established in less than one minute, whereas at the TEP in about 2-3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the formed complex. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH value of 3.59. Reverse titrations were also performed and accurate and repoducible results were obtained. The influence of the hetrogeneity of the pyrite on the accuracy of the results was investigated.