Determination of metastable zone widths and the primary nucleation and growth mechanisms for the crystallization of disodium guanosine 5′-monophosphate from a water-ethanol system

Metastable zone widths (MSZWs) and induction times (tind's) were measured by turbidity techniques during the antisolvent crystallization of disodium guanosine 5′-monophosphate (5′-GMPNa₂). Measured MSZWs can be affected by numerous process parameters, including temperature, the agitation rate, and the antisolvent addition rate. An exponential equation was used to correlate the supersolubility and solubility data for different conditions, and to afford predictions of the MSZW values. Values of t_ind at different temperatures and mole fractions of water were assessed to determine the primary nucleation and growth mechanisms of 5′-GMPNa₂ crystals in the water-ethanol system. The measured t_ind's were then correlated using mononuclear and polynuclear mechanistic models. The fitting results identified the primary nucleation mechanism for 5′-GMPNa₂ as polynuclear, which relates t_ind and the supersaturation for various growth mechanisms. The growth mechanism of 5′-GMPNa₂ was found to be diffusion-controlled at all experimental temperatures.