Potentiometric determination of ascorbic acid in water–acetonitrile solution using pyrite and chalcopyrite electrodes

Abstract

© 2016, Springer-Verlag Berlin Heidelberg. Performance characteristics of the solid-state potentiometric sensors, based on natural sulfide minerals pyrite and chalcopyrite, are assayed in aqueous and non-aqueous medium. The electrodes are simply and quickly prepared using inexpensive material that originate from natural environment. The pyrite and chalcopyrite electrodes exhibit good sensitivity and repeatability, stable potential with respect to time, short response time (less than 15 s), the sub-Nernstian response, with a slope of 48.0 mV per decade for pyrite and 41.6 mV per decade for chalcopyrite over a wide concentration range of copper(II) ion in acetonitrile, and a possibility of application without a time limit in aqueous and non-aqueous solution, as well. The practical applicability of these indicator electrodes is their utilization in potentiometric determination of L-ascorbic acid in water and water-acetonitrile, by using Cu(II) solution as the titrant, in pure compound and pharmaceutical formulations. The determination of 10.5–11.5 mg (0.50 mL) of L-ascorbic acid shows average recoveries of 98.2–101.9 %, with relative standard deviations of 0.1–0.9 %. The results show that the large potential break is obtained at the equivalence point when the titration was carried out in the presence of chelating bidentate ligand, neocuproine. This is a very simple, precise, reliable and sensitive one-step method, suitable for work in the laboratory and can be carried out directly, without any prior treatment of the investigated samples.