Fractional Determination of Small Amount of Water in Sodium Bicarbonate Powder

Abstract

Sodium bicarbonate is so unstable that the rate of decomposition is strongly affected by even trace amount of water in the powder. Variously hydrated species may be formed on the surface as decomposition products from sodium bicarbonate to sodium carbonate. In order to clarify the decomposition-mechanism and chemical-stability of the material, a method of quantitative analysis has necessarily been developed to determine the minute amount of free water and crystalline water related to variously hydrated salts. Preceded to the present work, therefore, four analytical methods established so far were examined to select the suitable method for the present object. The Karl-Fischer titration method combined with a moisture evaporator was finally selected by adding an analytical process, in which the dehydration amount-time profile is deconvoluted into several different peaks corresponding to the state of water. The fractional evaporation of various states of water enables the quantitative analysis without any pretreatment of the sample. This fractional quantitative analysis may be explained by the difference of thermal-stability among those of sodium bicarbonate, sodium carbonate hydrate and sodium sesquicarbonate.