Nitrogen content of amidosulfuric acid assayed by coulometric titration with electrogenerated hypobromite ions: establishment of SI traceability of nitrogen involving amidosulfuric acid, ammonium chloride and sodium chloride

Abstract

The nitrogen content of amidosulfuric acid was first measured directly by coulometric titration. Ammonium ions generated by decomposition of amidosulfuric acid were oxidized with electrogenerated hypobromite ions to nitrogen gas, and the amount of which was linked to the International System of Units (SI) based on Faraday’s laws of electrolysis. Conditions of the decomposition in an acidic medium were examined under different periods of heating. The comprehensive evaluation of the measurement uncertainties for amidosulfuric acid as an acid and as nitrogen was carried out, resulting in the establishment of a certified reference material (CRM) for both measurands with SI traceability. A novel measurement method for nitrogen content of amidosulfuric acid was ascertained. The relationship of three materials, amidosulfuric acid, ammonium chloride and sodium chloride, was also presented. The traceability among three materials was clarified through three different reactions, neutralization, oxidation-reduction and precipitation reactions. The assays of these materials were all consistent; consequently, the accuracy of measurement methods used was ascertained. Providing the CRM with the SI traceable nitrogen content enables one to obtain reliable analytical data in several applications such as the Kjeldahl method.