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A coulometria e considerada o metodo de maior qualidade metrologica para medicao de quantidade de substância de padroes primarios. Entretanto, a contaminacao de sais de elevada pureza esta presente em niveis tracos sendo necessaria a sua identificacao e quantificacao. Este trabalho apresenta os estudos desenvolvidos pelo Inmetro (Instituto Nacional de Metrologia, Normalizacao e Qualidade Industrial, Brasil) para determinar a pureza do cloreto de potassio (KCl) por titulacao coulometrica a corrente constante, alem da determinacao do brometo como seu principal contaminante por cromatografia ionica (IC). Esses estudos foram necessarios para desenvolver material de referencia certificado (MRC) de KCl para garantir a qualidade dos resultados das medicoes quimicas principalmente as de titulometria. A caracterizacao do candidato a MRC de KCl apresentou pureza de 99,9662%, a qual foi obtida apos a correcao do brometo, em fracao massica, obtido por IC, de 182,47 ± 3,03 mg kg -1 (incerteza expandida, k = 2, para um nivel de confianca de aproximadamente de 95%). 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.

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