Effects of Different Organic Acids on Solubility and Metastable Zone Width of Zinc Lactate

摘要

Effects of three different organic acids including racemic malic acid, succinic acid, and citric acid, which act as an impurity on the solubility and metastable zone width of zinc lactate (ZnL2), have been studied. The results show that the presence of all examined impurities increases the solution solubility and the values of solubility increase with increasing impurity concentration. The introduction of impurity also leads to a reduction on the metastable zone width, and the reductions are pronounced when the impurity concentration increased. Further, experimental data of metastable zone width were analyzed using die expression of the Nyvlt's approach and self-consistent Nyvlt-like approach, which can be expressed in the form: ln(ΔT_(max)/ T0) = Φ + β In b, with intercept Φ = {(l - m)/m}ln(ΔH_d/RT_(lim_) + (l/m)ln(f/KT0) and slope β - 1/m. Here T0 and T_(lim) are the saturation and nucleation temperature, respectively, m is the apparent nucleation order, and K is a new nucleation constant related to the factor / defined as the number of stable nuclei per unit volume, ΔH_d, the heat of dissolution and R the gas constant. Comparing to the former one, the latter approach provides a more satisfactory estimation for the metastable zone width at varying saturation temperature T0. The constant β for specific system reveals independence of the temperature, while the constant O increases with increasing saturation temperature. In addition, both constants are proportional to the impurity concentration. Crystal habits of final products are also influenced in the presence of impurities, but the crystal structures are barely changed.