Solubility and Pseudo-polymorphic Transitions of L-Serine in Water-Methanol System
Luk, Chee-wei Jennifer
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The research addressed in this thesis is focused on the solubility and pseudo-polymorphic transition of L-serine in mixed water-methanol systems. Cooling re-crystallizations were carried out that varied both temperature and methanol concentration. Solubilities were measured with high-performance liquid chromatography. It is found that the solubility increased with increase in temperature and decreased drastically with methanol concentration. The effect of temperature at which there is a transition of L-serine crystals from the rod-shaped (anhydrous) form to hexagonal (monohydrate) form was confirmed and that transition temperatures decreased with methanol concentrations in a non-linear manner. The solubility data were correlated and plotted using the vant Hoff equation and the enthalpy and entropy of dissolution were determined. These values increased with increase in methanol concentration. The solid crystals were analyzed by optical microscopy and powder X-ray diffraction. The rod-shaped crystals were identified to be anhydrous L-serine, while the hexagonal crystals were L-serine monohydrate. Dehydration of the monohydrated crystals in their solid-state was examined and the onset of such phenomenon was known to start once the crystals were removed from the solutions.