Solubility and modeling acid–base properties of adrenaline in NaCl aqueous solutions at different ionic strengths and temperatures

Abstract

Solubility and acid–base properties of adrenaline were studied in NaCl aqueous solutions at different ionic strengths (0<I/molL−1<3.0) and temperatures (T=298.15 and 310.15K), by means of different techniques: potentiometry, UV-spectrophotometry and spectrofluorimetry. The intrinsic solubility of the ligand was calculated from simple mass balance equations, by using the free hydrogen concentration and the protonation constants of the ligand determined in the same experimental conditions of the solubility measurements. The salting-In or Out parameters and the activity coefficient of the neutral species were calculated by means of the Setschenow equation.The dependence of the protonation constants on the ionic strength was modeled by means of the Debye–Hückel type equation and of the SIT (Specific ion Interaction Theory) approach. The specific interaction parameters of the ion pairs were also reported. For the protonation constants, the following thermodynamic values at infinite dilution were obtained: T=298.15K, logK1H0=10.674±0.018 and logK2H0=8.954±0.022; T=310.15K, logK1H0=10.355±0.018 and logK2H0=8.749±0.030.