l-Gln is stable around the isoelectric point (pH 5.65), but if the pH shifts from the isoelectric point to either acid or alkaline conditions, l-Gln is easily hydrolyzed to l-glutamic acid and ammonia. To find a proper solvent with the view of drowning-out crystallization and avoiding degradation, an experimental work devoted to collect information on the solubility of l-Gln in the ternary system ethanol + water, acetone + water was carried out.
Innumerable techniques, of almost infinite variety, have been proposed at one time or another for the measurement of the solubility of solids in liquids. No single method can be identified, however, as being generally applicable to all possible types of system. The choice of the most appropriate method for a given case has to be made in the light of the system properties, the availability of apparatus and analytical techniques, the skill and experience of the operators, the precision required, and so on [5] and [6]. Due to the fact that l-glutamic acid, the degradation product of l-Gln, has almost equal molar weight 147.15, with l-Gln 146.17, l-Gln degradation would not affect the saturated solution concentration measurement by weighing method. Therefore, gravimetric method is feasible to measure the solubility of l-Gn in the low temperature range.