Feasible stoichiometric reactions for SI traceable bromate assays

Abstract

Evaluating chemical purities by different analytical methods based on different reactions is one of the effective approaches to decrease the contribution of unknown biases that each method has, and to establish reliable reference materials. This paper describes new applications of precipitation titration with silver(I) and redox back titration with iron(II) to the assays of bromate ions which were different from a conventional titrimetric reaction with thiosulfate ions. Bromate ions are often used as a standard for redox titration as well as for evaluating water and food quality by instrumental analyses. Required measurands in these instrumental analyses are not redox properties of the ions, but the mass fraction in chemicals. Bromate ions have been determined by a conventional redox titration: iodine (triiodide) liberated by bromate ions in an acidic potassium iodide solution has been titrated with a standardized sodium thiosulfate solution. New titrimetric approaches described in the present paper directly allow to evaluate the mass fraction of the ions without iodine liberation processes in the conventional reaction, and contribute reliable analytical assays. These approaches were also attempted to the assays of iodate ions, which is one of the useful standards.