Since the sulfate ion is a main impurity contained in highly pure salt products manufactured through a dissolution purification process, controlling the content of the sulfate ion in the salt products is important concerning the aspect of salt production. The authors studied a simple method for determining the sulfate ion content by IR diffuse reflectometry and, as a result, developed a simple determining method capable of determining the sulfate-ion content of highly pure salts without destruction and with a smaller determining error of around ±10 mgkg
-1 and a higher repetition accuracy (RSD), of 4.6%. In this method, the peak strength of SO degenerate stretching vibrations specific to the sulfate ion, which was determined by IR diffuse reflectometry, is corrected using the variation of the K-M value of 1900-2090 cm
-1 caused by effects of the filling condition, particle size and particle-size distribution of the test sample on the degree of light scattering; also, the effects of the ambient temperatures and humidity are corrected using the absolute humidity. This method has sufficient accuracy for a simple determination, which enables a sulfate ion determination within a short time of approximately one minute, and is therefore, considered, to be thoroughly adaptable to product and process control.
View full abstract