and As(III) with standard potassium permanganate solution, are presented. The titration end point (TEP) was detected with a universal electrode whose sensor is natural crystalline pyrite. The titrations of As(III) were carried out in HCl (1.2 M) and H 2 SO 4 solutions (0.1-4.5 M), whereas oxalate was determined in H 2 SO 4 (0.1-4.5 M). Iron(II) and hexacyanoferrate(II) were titrated in H 2 SO 4 and also in H 3 PO 4 solutions (0.1-4.5 M). The titrations of Mn(II) were performed in H 2 P 2 O 7 2-media at pH 4.0, 5.0, 6.0 and 7.0. The results obtained by using the pyrite electrode were compared with those obtained by the application of a Pt-electrode, and good agreement, reproducibility and accuracy were obtained. The potentials in the course of the titration and at the end-point (TEP) are rapidly established. The potential changes at the TEP ranged from 90 to 330 mV/0.1 mL, depending on the titrated system. The highest changes were observed in titrations of Fe(II) in H 3 PO 4 (240-330 mV/0.1 mL). Reversed titrations were also performed and accurate and reproducible results were obtained.
The potentiometric titration of chloride, bromide, iodide and thiocyanate with silver nitrate, using the mineral pyrite as a sensor for the detection of the end-point, is described. The potentials of the pyrite electrode were found to be established rapidly, and accurate and reproducible results were obtained. The pyrite electrode potential showed a sub-Nernstian dependence on the concentration of the ionic species investigated. In addition, lead(1r) was determined by titration with potassium chromate and chloride by titration with standard mercury(1) solution. Accurate and reproducible results were also obtained in the reverse titrations.
Natural monocrystalline pyrite as a new indicator electrode for the potentiometric titration of weak acids in acetonitrile, propionitrile and benzonitrile was studied. The investigated electrode showed a linear dynamic response for p-toluenesulfonic acid concentrations in the range from 0.1 to 0.001 M, with a Nernstian slope of 74 mV per decade. Sodium methylate, potassium hydroxide and tetrabutylammonium hydroxide (TBAH) proved to be very suitable titrating agent for this titration. The response time was less than (11 s) and the lifetime of the electrode is long. The advantages of the electrode are log-term stability, fast response, and reproducibility, while the sensor is easy to prepare and of low cost.
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