Investigation on drying conditions and assays of amidosulfuric acid and sodium carbonate by acidimetric coulometric titration and gravimetric titration |
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Authors: | Toshiaki Asakai Akiharu Hioki |
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Institution: | (1) National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 3-9, 1-1-1 Umezono, Tsukuba Ibaraki, 305-8563, Japan |
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Abstract: | Amidosulfuric acid and sodium carbonate as standards for acid–base titrimetry were assayed by coulometric titration and gravimetric
titration. Amidosulfuric acid was directly assayed by coulometric titration with electrogenerated hydroxide ions, and sodium
carbonate was assayed by gravimetric back-titration. For sodium carbonate, excess amount of sulfuric acid, whose concentration
was determined by coulometric titration, was added to sodium carbonate, and then gravimetrically back-titrated using a sodium
hydroxide solution whose concentration was determined by gravimetric titration using the sulfuric acid. The accuracy of the
coulometric titration for amidosulfuric acid and sulfuric acid was evaluated by examining the current efficiency of pulse
electrolysis, the amount of the electrolysis current used, and the time spent for a titration. In addition, the drying conditions
for high purity primary standards have a significant effect on the titration results due to changes in the acid–base assay.
The suitable drying conditions for amidosulfuric acid and sodium carbonate were evaluated by mass-change measurements, coulometric
titration and gravimetric titration. The measurement uncertainties were estimated from the uncertainties on the titration
processes. Finally, the assays of amidosulfuric acid and sodium carbonate were 99.986% ± 0.010% (k = 2) after drying at 50 °C for 2 h, and 99.970% ± 0.016% (k = 2) after drying at 280 °C for 4 h, respectively. In addition, the international consistency was confirmed by measuring
certified reference materials (CRMs) available from different National Metrology Institutes, and the compatibility of values
among CRMs was experimentally ascertained. |
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