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 [5,6]. 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.