Constant-current coulometry and ion chromatography bromide determination to characterize the purity of the potassium chloride

Abstract

Coulometry is considered the highest metrological method for measuring the amount of substance of high-purity compounds. However, the contamination of the high purity salts is present in trace levels and its identification and quantification are necessary. This work aims to present the studies performed by Inmetro (National Institute of Metrology, Standardization and Industrial Quality, Brazil) to determine the purity of potassium chloride (KCl) by constant-current coulometric titration, as well as the determination of bromide as the main impurity in the KCl through ion chromatography (IC). These studies were needed to develop certified reference material (CRM) of KCl to guarantee the quality of the chemical measurements, mainly those performed by titrimetric analysis. The characterization of the candidate CRM of KCl by coulometric titration presented the purity of 99.9662%. This value was obtained after bromide correction of 182.47 ± 3.03 mg kg-1 (expanded uncertainty for k = 2, for a confidence level of approximately 95%) for the mass fraction bromide assayed by IC. © 2011 Sociedade Brasileira de Química.