Reductimetric determination of Nitroso-R-Salt with Iron(II) in buffer medium and in presence of oxalate and the speciation of Iron(III)-oxalate in the medium

摘要

Simple, rapid and accurate reductimertric titration methods (potentiometric and visual ) have been developed for the detetermination of Nitroso-R-Salt (a high potential chromogenic reagent ) using iron(II) as a reducing agent in buffer medium ( pH 4.0-5.0 ) and in presence of sodium oxalate (0.05M) and a small amount of methylene blue which acts as a catalyst as well as a redox indicator. Nitroso-R-Salt (NRS ) in the range 15-60mg has been determined with an accuracy of ±0.5% and ±0.7% in the case of potentiometric and visual end-point methods respectivesy. The precision in both the methods has been determined by computing pooled standard deviation and 95% confident limits. In this method NRS is reduced to its corresponding amino compound by iron(II) in a four electron reduction step. The formal redox potentials of the oxidant and reductant systems under the optimum titration conditios have been measured. Based on these potentiials,a satisfactory explanation for the observed redox reaction has been offered. Since oxalate is an iron chelator, a species distribution diagram indicating the extent of formation of various species in iron(III) – oxalate system has been generated using a computer program kown as HYSS.