Color Change of Sudan III against Concentrated Sulfuric Acid in Acetonitrile and Quantification for a Small Amount of Concentrated Sulfuric Acid

• Published in: Analytical Sciences Vol. 32; no. 2; pp. 129 - 133
• Main Authors: SAKURAI, Takao, KURATA, Shoji, OGINO, Kenji
• Format: Journal Article
• Language: English
• Published: Singapore The Japan Society for Analytical Chemistry 2016; Springer Nature Singapore; Japan Science and Technology Agency
• Subjects: Acetonitrile; Analytical Chemistry; Chemistry; Color; Dyes; Mathematical analysis; Original Paper; Protonation; quantification method; Spectroscopic analysis; Spectroscopy; Sudan III; Sulfuric acid; Sudan III; sulfuric acid; quantification method
• ISSN: 0910-6340; 1348-2246
• DOI: 10.2116/analsci.32.129

The color-changing phenomenon of hydrophobic bisazo dye, Sudan III in an acetonitrile solution against the addition of concentrated sulfuric acid has been discovered and the chromic properties investigated. Based on observations, a novel quantification method of concentrated sulfuric acid has been developed. Sudan III changes its color from orange to blue against a small volume of sulfuric acid, and the acetonitrile solution of Sudan III is the most suitable for observing the color-change phenomenon. 1H-NMR and UV-Vis spectroscopic studies showed that the color-change mechanism of Sudan III against sulfuric acid is due to the protonation of the dye by sulfuric acid. This phenomenon is applicable to the quantification of concentrated sulfuric acid by introducing the Hammett acidity function. The proposed method requires only a small amount of the sample, 0.04 mL, and enables rapid quantification.