The preparation of saturated solution
The traditional preparation process by isothermal method is as
follows [5–7]. The cylindrical double-jacketed glass vessel was controlled
to a constant temperature with continuous stirring, in which
the temperature was controlled to be constant with a precision of
±0.05 K through a thermostatic bath (Type 501 A, China). Then,
excess solute was added to the solvent. After the temperature of
the water bath was kept constant for at least 4 h, the stirring was
stopped, and the solution was kept still for 3 h. A portion of the
upper clear solution was filtered with the membrane (0.45 m).
In terms of this method a long dissolution time (4 h) has an
increased risk of l-Gn degradation. Therefore, an experiment to
find a proper dissolution time is carried out. Excess solute was
added to the solvent, the concentration of suspension was measured
by weighing method (described later) at different dissolve
times. Fig. 2 gives the concentration variation of suspension along
with dissolution time. The suspension can reach the dissolution
phase equilibrium in short term,