Analytical Sciences

Coulometric Titration of Urea with Electrogenerated Hypobromite

Jun KATO,*,** Takuma KOSEKI,* Yukie AOKI,* Ayako YAMADA,* and Tatsuhiko TANAKA*

*Faculty of Engineering, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
**Nuclear Cycle Backend Directorate, Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai, Naka, Ibaraki 319-1195, Japan

A definitive method is described for the indirect assay of several tens of milligrams of urea by coulometric titration. Urea was decomposed in concentrated sulfuric acid using a Kjeldahl flask. Subsequently, the formed ammonium ion was titrated with electrogenerated hypobromite ion in a sodium bromide-sodium tetraborate medium of pH 8.6, with amperometric end-point detection. Parameters affecting the pretreatment procedure were evaluated. The optimized conditions included the heating of 2 g of urea at around 300°C for 2 h with 10 cm³ of sulfuric acid. Under the proposed conditions, the assay value with expanded uncertainty (k = 2), 99.870 ± 0.026%, agreed well with the certified value of NIST SRM 912a urea, 99.9 ± 0.1%.

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