2.2.2. The concentration determination of saturated solution
A portion of the upper clear solution prepared by the above method was filtered with the membrane (0.45 μm) and preserved in a weighted double dish which had been completely dried.
The double dish was quickly weighed to determine the mass of the sample.
The solvent in the double dish was completely evaporated after 10 h with the oven at 60 °C; the double dish was reweighed to determine the mass of the residue solid and the evaporated solvent.
All of the masses were measured using an electronic balance with an uncertainty of 0.0001 g.
During the drying process at 60 °C l-Gln degradation is inevitable. To this end, an experiment was conducted to test the influence of this drying process on the measured concentration of l-Gn in solution.
A series of solutions with different concentrations of l-Gn were dried by the above process.
The calculated concentration based on the mass of the residue solid and the evaporated solvent and the actual solution concentration were compared in Fig. 3.
The results showed this drying process in experiment does not affect the concentration calculation of l-Gn in solution.