Development of a Reference Material for Potassium Bromide Composition

To obtain reliable measurement results for the content of components in various materials, reference materials with certified content of the studied component are required. Elemental bromine, being a volatile and toxic liquid, is unsuitable as a source material for the preparation of a reference material for the chemical element bromine. The most optimal choice for the reference material is a bromine salt – potassium bromide. The aim of the study is to develop a certified reference material for composition of potassium bromide based on the same high-purity salt with the certified characteristic «mass fraction of potassium bromide». The mass fraction of the main component in potassium bromide was measured using two methods: a direct method employing coulometric titration with corrections for interfering impurities determined by ion chromatography, and an indirect method based on the scheme of 100% minus the sum of impurities, taking into account their ionic forms. It is shown that the direct and indirect methods for determining the mass fraction of potassium bromide yield consistent results: (99.871 ± 0.029) and (99.873 ± 0.017)%, respectively. Studies of homogeneity, as well as short-term and long-term stability, were conducted using the coulometric titration. A reference material for potassium bromide composition, GSO 12300-2023, was developed with an interval of certified values of the mass fraction of potassium bromide (99.5–100)% and an expanded uncertainty of the certified value of 0.05% at k=2. The certified value and expanded uncertainty of the mass fraction of potassium bromide for a batch of the reference material were (99.87 ± 0.05)%. A distinctive feature of the indirect method for determining the mass fraction of potassium bromide implemented in this work is the construction of a chemical composition model of the analyzed object. This model is based on both a priori and experimental data and utilizes two fundamental principles when summing impurity contents: the condition of material (mass) balance and the principle of electroneutrality. The described indirect method is sufficiently universal. For high-purity salts, it enables achieving a relative expanded uncertainty (at k=2) of less than 0.02%. This method can be adopted in analytical practice for assessing the purity of other metal salts where high accuracy is required. The developed certified reference material can be used to ensure the metrological traceability of measurement results in both titrimetry (precipitation titration) and elemental analysis. It can also be utilized for the preparation or control of certified values for reference materials of bromide ion solution composition, including those in multicomponent mixtures with other anions.