Determination and correlation of solubility of thiamine nitrate in water+ethanol mixtures and aqueous solution with different pH values from 278.15K to 303.15K

Abstract The solubility of thiamine nitrate in water + ethanol binary solvent mixtures and aqueous solution with different pH values was determined at temperatures from 278.15 K to 303.15 K by a laser monitoring observation technique at atmospheric pressure. The experimental solubility in water + ethanol system was correlated by the modified Apelblat equation and the CNIBS/R-K model, which both agree well with the experimental results. The dissolution enthalpy, entropy and Gibbs energy of thiamine nitrate were obtained by the van’t Hoff equation. The obtained results indicate that the dissolution process of thiamine nitrate is endothermic and entropy-driven. To evaluate the effect of pH value on the solubility of thiamine nitrate in aqueous solution, the Henderson–Hasselbalch (HH) equation was adopted to correlate the experimental solubility and the pH value. It is found that the experimental solubility precisely follows the HH equation and the pH value has a big impact on the solubility of thiamine nitrate at a given temperature. Besides, in this work, to account for the combined effect of pH value and temperature on the solubility of thiamine nitrate in aqueous solution, a modified equation based on the HH equation was established for the first time, and it shows a good correlation between the experimental data and the calculated results.