Use of Sulphide Minerals as Electrode Sensors for Acid-Base Potentiometric Titrations in Non-Aqueous Solvents and Their Application for the Determination of Certain Biologically Active Substances

The use of certain sulphide minerals as electrode sensors, for acid-base potentiometric titrations in propionitrile/ethylene carbonate and nitromethane/ethylene carbonate as solvents, was investigated. The coulometrically generated base was obtained by the cathodic reduction of m-cresol and 3-methoxy phenol in the above mentioned solvents and it was used for the potentiometric titration of p-toluenesulphonic, trichloroacetic, 5-sulphosalicylic and oxalic acids. For the potentiometric determination of the equivalence point, the use of the following electrode couples was investigated: glass SCE, FeS2-SCE, CuFeS2-SCE, PbS-SCE, CuS-SCE and Cu2S-SCE. The natural minerals pyrite, chalcopyrite, galena, covellite and chalcocite were used as the indicator electrode sensors for the potentiometric determinations of some organic acids and bases, which represent biologically active substances, and also some substances that are toxic for the environment. The electrodes used for this purpose showed a linear dependence of the potential on the logarithm of the concentration of p-toluenesulphonic acid in the concentration range 0.5 to 100 mmoldm(-3) with a sub-Nernstian slope. The standard deviation for such determination is less than 0.9%.