Thermodynamic Study on the Interaction of Nicotinic Acid with H + , Na + , Ca 2+ and Mg 2+ at Different Temperatures and Ionic Strengths

Protonation of nicotinic acid has been investigated by means of potentiometric titrations at different temperatures 283.15 ≤ T (K) ≤ 383.15 and ionic strengths of NaCl (aq) , 0.12 ≤ I (mol·kg −1 ) ≤ 4.84 and mixed NaCl with MgCl 2 or CaCl 2 . Stability constants of the CaL + and MgL + species were obtained by means of the Δp K method. Different models (e.g. Debye–Hückel type equation, Specific Ion Interaction Theory, Pitzer and van’t Hoff) were applied to account for the ionic strength and temperature dependences, in order to obtain data in a standard state and parameters to calculate stability constants in any point of our experimental domain. Speciation studies were performed simulating the conditions of natural fluids. Literature data were investigated for comparison with the experimental results here obtained.