Aqueous solubility of calcium citrate and interconversion between the tetrahydrate and the hexahydrate as a balance between endothermic dissolution and exothermic complex formation

TY - JOUR

T1 - Aqueous solubility of calcium citrate and interconversion between the tetrahydrate and the hexahydrate as a balance between endothermic dissolution and exothermic complex formation

AU - Hedegaard, Martina Vavrusova

AU - Skibsted, Leif Horsfelt

PY - 2016

Y1 - 2016

N2 - Aqueous solubility of calcium citrate tetrahydrate was found to decrease with increasing temperature, while solubility of hexahydrate increased with a transition temperature at 51.6 °C. Excess citrate increased calcium citrate solubility but decreased the calcium ion activity of the saturated solution with an initial solubility overshooting to form supersaturated solutions indicating binding of calcium to citrate with an association constant of 3.6 ± 0.1 × 104, δHo = -5.07 ± 0.04 kJ mol-1, δSo = 70.3 ± 0.3 J mol-1 K-1 at 25 °C. Dissolution of the tetrahydrate and hexahydrate was found to have δHo = 27 ± 9 kJ mol-1, δSo = -218 ± 30 J mol-1 K-1 and δHo = 57 ± 7 kJ mol-1, δSo = -126 ± 24 J mol-1 K-1, respectively, as determined from the temperature dependence of solubility corrected for complex formation. The exothermic complex formation results in inverse solubility only for the tetrahydrate with its moderate endothermic dissolution, which also precipitates at ambient temperature rather than the less soluble hexahydrate.

AB - Aqueous solubility of calcium citrate tetrahydrate was found to decrease with increasing temperature, while solubility of hexahydrate increased with a transition temperature at 51.6 °C. Excess citrate increased calcium citrate solubility but decreased the calcium ion activity of the saturated solution with an initial solubility overshooting to form supersaturated solutions indicating binding of calcium to citrate with an association constant of 3.6 ± 0.1 × 104, δHo = -5.07 ± 0.04 kJ mol-1, δSo = 70.3 ± 0.3 J mol-1 K-1 at 25 °C. Dissolution of the tetrahydrate and hexahydrate was found to have δHo = 27 ± 9 kJ mol-1, δSo = -218 ± 30 J mol-1 K-1 and δHo = 57 ± 7 kJ mol-1, δSo = -126 ± 24 J mol-1 K-1, respectively, as determined from the temperature dependence of solubility corrected for complex formation. The exothermic complex formation results in inverse solubility only for the tetrahydrate with its moderate endothermic dissolution, which also precipitates at ambient temperature rather than the less soluble hexahydrate.

U2 - 10.1016/j.idairyj.2016.02.033

DO - 10.1016/j.idairyj.2016.02.033

M3 - Journal article

AN - SCOPUS:84960492226

SN - 0958-6946

VL - 57

SP - 20

EP - 28

JO - International Dairy Journal

JF - International Dairy Journal

ER -